Answer these 16 Short questions related to Immunology

ImmunologyQ#1 Please briefly describe the mechanism (hypersensitivity) behind the development of
Graves’ disease.
Q#2 Describe the type II hypersensitivity reaction that can occur in an Rh+ infant of an
Rh- mother.
Q#3 Mucosal tolerance is achieved in the intestine by sampling bacteria or antigen from the
intestinal lumen. Please define “mucosal tolerance” and provide one example of how
antigen sampling occurs in the intestine under homeostatic (normal) conditions.
Q#4 Define what a chemokine is. Identify one chemokine and its receptor and describe
what cells express this chemokine and what cells express the receptor and describe the
chemokine function.
Q#5 Provide 2 differences between antibodies secreted from a primary focus versus a
germinal center.
Q#6 Cytokines secreted by the different subsets of CD4+ T cells negatively regulate the
development of other subsets. Provide three examples of how cytokines regulate the
development of other subsets. Identify the cytokine and target T helper cell involved.
Q#7 Expression of CD25 and CD69 is upregulated in T cells immediately after TCR
stimulation. Explain the role of CD25 and CD69 in T cells and describe their molecular
mechanism in a few sentences for each molecule.
Q#8 An estimated 90% of all thymocytes do not mature into T helper or T cytotoxic cells.
Describe the mechanism by which thymocytes die and provide two explanations for this
excessive cell death.
Q#9 A patient presents with recurrent bacterial infections. A work-up shows that the
patient has both B cells and T cells. Further analysis shows that the patient has high levels
of IgM but an absence of IgG, IgA and IgE in the serum. Name one gene defect that could
lead to this phenotype and briefly explain how this leads to the observed alterations in
antibody levels.
Q#10 How does desensitization therapy work as a treatment modality for Type I
hypersensitivity?
Q#11 Describe the two different zones of a germinal center with respect to chemokine
expression, Tfh cells. Provide 2 molecules that the Tft cells use to help germinal center B
cells.
Q#12 Activated endothelial cells and smooth muscle cells in early atherosclerotic plaques
produce the chemokine CCL2. Describe how this leads to disease progression.
Q#13 Please briefly describe the cause of kidney inflammation in patients suffering from
Lupus. Please mention the specific type of hypersensitivity involved.
Q#14 Cd4 mice and Cd8-/- mice lack CD4T and CD8T cells, respectively. Explain why,
with regards to the molecular function of CD4 and CD8 (in 1-2 sentences total).
Q#15 What is the pre-TCR and describe two of the functions of the pre-TCR.
Q#16 An antigen-presenting cell activates a T cell in the Peyer’s patch or mesenteric lymph
node. Describe how the activated T cell homes to the intestine to elicit an appropriate
effector response. Please include the molecules important for this process in your answer.
B Cell Generation, Activation and
Differentiation which leads to antibody
secretion: a.k.a. Humoral Immunity
Jason Weinstein PhD
jw1194@njms.rutgers.edu
Objectives
You should be able to:
1. Describe the steps required for B cell maturation
in the bone marrow
2. Describe the events leading to the generation of a
germinal center and differentiation of B cells to
antibody secretion by plasma cells
3. Understand the mechanisms by which Somatic
Hypermutation and Class Switching occur
4. Describe antibody functions, including the part
played by the constant region (Fc) portion of the
antibody molecule.
Antibodies are bifunctional proteins with key
activities in host defense
Binds antigen
•“antigen” = target
molecule
•Binding can
neutralize or block
antigen activities (e.g.
toxins, viral entry
receptors)
Triggers immune
response
• Engages Fc
receptors on
immune cells
• Binds complement
Antibodies mediate humoral immunity
Figure 10.1 Janeway 10th ed.
•
•
Antibodies can neutralize and clear pathogens, often before
they begin to replicate in the host.
Their antigen binding specificity is determined by the V region,
the biological activity by the C region
Antibodies Also
Neutralize
Bacterial Toxins
• Many common
diseases are
caused by
bacterial toxins
• Toxin-specific
antibodies can
block the binding
of toxins to their
cell surface
receptor
Figure 10.60 Janeway 10th ed.
Opsonization and Complement Activation
Figure 10.33 Janeway 10th ed.
• Antibodies bound to bacteria allow binding to Fc receptors on
macrophages and neutrophils
• Activation of complement by antibody binding allows
components bound to the bacterial surface to bind complement
receptors on macrophages and neutrophils
NK Cell Binding and Activation
Figure 10.42 Janeway 10th ed.
• NK cells protect against intracellular pathogens
• Antibodies binding to foreign antigens on the cell surface
are recognized by Fc receptors on NK cells
• FcR cross-linking signals the NK cell to kill
B cell life cycle
Figure 8.2 Janeway 10th ed.
Overview of VDJ and the Selection
B220
Clinical Immunology (Fifth Edition)
Remember this: B cell development
Figure 8.4 Janeway 10th ed.
•
•
•
Heavy chain rearrangement is first, and signaling through the pre-B
receptor precludes further V-DJ rearrangements
Large pre-B cells undergo cell division, light chain rearrangements then
proceed
BUT each B cell expresses only one rearranged VDJ and one
rearranged light chain.
Deletion of self-reacting clones
in the bone marrow
• If a BCR does not cross-react
with self, the B cell then matures
and moves into the periphery.
• If the BCR is strongly cross linked
by self antigens, B cell
development stops, and light
chain rearrangement
recommences.
Figure 8.10 Janeway 10th ed.
Light Chain Rearrangements are often nonfunctional, but repeated rearrangements occur
• 2/3 rearrangements are
unsuccessful
• K light chains are
rearranged first, if this
doesn’t work, λ chain
rearrangement
commences.
• But only one light chain
is expressed in a given
cell
• Clonal expansion prior to
light chain
rearrangement means
that a given VDJ H chain
rearrangement, can be
paired with multiple
different light chains
Figure 8.8 Janeway 10th ed.
Self-reacting B cells in the bone marrow
• If there is no reaction to
self antigens in the bone
marrow, the B cell
matures and migrates to
the periphery
• If the BCR is strongly
cross-linked by self
antigens (like MHC),
development is arrested.
• Cross-linking by soluble
self proteins leads to
anergy
• B cell development
continues when BCR
binding to a self antigen
does not result in crosslinking. These cells are
potentially self reactive,
but cannot, or have not
yet, been activated by
antigen binding
B cell life cycle
Figure 8.2 Janeway 10th ed.
B cells must be activated AND differentiate to
secrete antibodies
Figure 10.9 Janeway 10th ed.
B Cell activation is initiated by BCR binding
and internalizing antigen
• Antibody production requires B cell
activation.
• Naïve B cell activation requires a stimulus
beyond antigen binding alone.
• Generally this requires BCR cross-linking by
antigen binding, but also T cell help.
• The B cell acts as an antigen presenting
AND antigen binding cell.
CD4 T Cells Help:
CD8 T cells Kill
• As well as providing a signal
through the BCR, antigen
bound to the BCR is
internalized and degraded
• Only the viral coat protein is
recognized by the BCR shown
here, but the entire virus is
digested after internalization
CD4 T Cell Help
• Peptides derived from all viral
proteins are presented at the cell
surface bound to MHCII
molecules
• T cells recognizing ANY viral
peptide can provide T cell help to
the B cell
• T cell help consists of cytokine
production in response to TCR
recognition of the viral peptide
AND CD40-CD40L interaction
Where the action is: Secondary Lymphoid
Tissue
• B cells meet up with their
antigen in secondary
lymphoid tissues (spleen,
lymph nodes, tonsils,
peyer’s patches)
• Naïve B cells enter primary
lymphoid follicles from
lymph or blood
Figure 10.10 Janeway 10th ed.
T follicular helper CD4 T cells (Tfh) Cells
Produce Factors Required for B cell Activation,
Proliferation and Differentiation
Plasmablast
Figure 10.3 Janeway 10th ed.
CD40-CD40L interaction is important for driving B cells into
the cell cycle, and promotes class switching and somatic
hypermutation.
Plasmablast = short lived (2-4 days) make primarily IgM after
primary response
Tfh cell development requires DCs and B cells
Spleen
Tfh cell development requires DCs and B cells
Infected
tissue
Spleen
Tfh cell development requires DCs and B cells
Infected
tissue
Spleen
Tfh cell development requires DCs and B cells
Infected
tissue
GATA3
Spleen
Tbet
Bcl6
Bcl6
Bcl6
Antigen is brought to B cells in follicle
Figure 10.7 Janeway 10th ed.
Antigens from
viruses and
bacteria enter
the lymph node
via the afferent
lymphatics and
are taken up by
macrophages in
the subcapsular
sinus or follicular
dendritic cells.
Naïve B cells
that encounter
an antigen they
recognize
become
activated and
move to the
edge of the T
cell zone where
they encounter T
cells activated
by the same
response.
Recap
B cells enter the lymph node from the
blood and stay in the follicle.
If they are activated 1) by binding
antigen and 2) by T cell help
most of the activated B cells will
proliferate and and form a germinal
center.
Some will instead move to the outer
edge of the follicle and form a primary
focus.
B cells from the primary focus will
differentiate into short lived (2-4 days)
plasmablasts. Producing low affinity
antigen specific IgM.
Figure 10.10 Janeway 10th ed.
Primary focus
Figure 10.13 Janeway 10th ed.
Germinal Center
3 steps of the Germinal Center
response (Overview)
1
3 steps of the Germinal Center
response (Overview)
2
FDCs do not
internalize
antigen, which can
persist intact.
Antigen may be
bound via Fc
receptors or
complement
receptors.
Figure 10.16 Janeway 10th ed.
Figure 10.17 Janeway 10th ed.
3 steps of the Germinal Center
response (Overview)
2
3 steps of the Germinal Center
response (Overview)
Tfh
3
What the B cell follicle really looks like
Figure 10.12 Janeway 10th ed.
GC B cells migrate back and forth between the dark
and light zones until they have a high enough affinity
GC B cells down regulate
CXCR4 to leave the DZ
GC B cells
upregulate
CXCR4 to enter
back
into the DZ
Somatic hypermutation (SHM)
• Somatic hypermutation only takes place in the
germinal centers
• Somatic mutation is not a constitutive process in
B cells; it is turned on in the dark zone and off
in the light zone
• Introduces mutations in VDJ regions that
change anywhere from one to a few amino acids
• Resulting in new closely related B-cell clones
that BCR differ subtly in specificity and antigen
affinity or new antigen specificity
V genes of both heavy and light chains acquire more
mutations as the GC response goes on
Figure 10.14 Janeway 10th ed.
Bcl6
• Bcl6 modulates the
expression of genes involved
in GC B cell differentiation,
cell cycle, and maintenance
of GC B cells
• Bcl6 suppresses the
induction of DNA
damage response
during SHM
AID
Only germinal center B cells express the
enzyme Activation-Induced Cytidine
Deaminase (AID)
– Deaminates cytidine residues in ss DNA
during active transcription
– The presence of uracil in DNA triggers
repair by either the mismatch repair of
base-excision repair pathways,
introducing mutations into the V regions
Figure 10.18 Janeway 10th ed.
So now you know HOW somatic
mutations occurs but HOW does
that result in affinity maturation
(selecting the strongest B cell)
Affinity Maturation
Most mutations will decrease affinity
of the BCR for antigen and these
are eliminated
Rarely a mutation increases affinity.
In the light zone these cells are
selectively expanded. They can
more effectively capture antigen
and present to TFH cells and receive
T cell help (CD40 and cytokines)
Figure 10.15 Janeway 10th ed.
Affinity Maturation
B cells receiving T cell help can
return to the dark zone for additional
cycles of proliferation and mutation.
The result of this iterative process is
antibodies with V regions with
increased antigen-binding efficiency
Figure 10.15 Janeway 10th ed.
Does this make more sense now?
Tfh
3
To B Cell Memory or not T B cell Memory
(Plasma cell)…
• Memory B cells leave the GC after 1-3
rounds of divisions and recirculate for
years, restarting this whole GC process
upon reactivation
• Plasma cells arise from GC B cells that
have undergone 6-7 rounds in the GC
• Plasma cells move into the bone marrow
where they continue to pump out antibody
for 1-80 years
Results of a germinal center reaction
Bone marrow
Germinal center
LZ
DZ
Adapted from: https://www.immunology.org/public-information/bitesized-immunology/cells/b-cells
Secondary lymphoid organs
Primary focus
Figure 10.13 Janeway 10th ed.
Germinal Center
Class Switch…according to the textbook
• Occurs after B cell activation by TH cells
– Rarely in primary foci
– Primarily in germinal center
• Requires AID and CD40-CD40L interaction
• Patients lacking either AID or CD40L cannot undergo
class switching and have a severe immune deficiency
(Hyper-IgM syndrome)
Figure 5.16 Janeway 10th ed.
How Class Switching works
• Class switch is also mediated
by enzymes including AID
which introduce nicks into the
template DNA
• Switch regions are present
upstream of each of the
potential constant region loci
• Switching is driven by
initiation of transcription at an
upstream promoter (choice of
promoter is cytokine driven)
Figure 5.16 Janeway 10th ed.
Class switching part 2, arranging the DNA…looks
strangely familiar
• Like VDJ rearrangements,
DNA repair enzymes help to
repair the break
• The 2 Switch regions are
brought together by the
DNA repair machinery and
the intervening DNA
sequences are excised
• The selected constant
region is now adjacent to
the VDJ region and the
regions before are removed
and never be used by that B
cell
Figure 10.13 Janeway 10th ed.
Cytokines made by TFH cells direct the choice
of isotype for class switching in T-dependent
antibody responses
Edited from Figure 10.23 Janeway 9th ed.
Why bother with class switching?
Figure 10.27 Janeway 10th ed.
*IgG is by far
most common
isotype in
circulation
Kinetics of antibody responses to primary
infection versus re-infection
Long lived plasma cells should provide plateau IgG Ab response
https://courses.lumenlearning.com/microbiology/chapter/b-lymphocytes-and-humoral-immunity/
T-Independent Antigens
Bacterial polysaccharides, polymeric proteins, lipopolysaccharides,
mitogens, lectins, viral antigens
TI-2 antigens
TI-2 antigens are
molecules with
highly repetitive
structures such as
capsular
polysaccharides.
These antibodies
are important in
the early stages of
an immune
response to
bacterial infection.
Mucosal Immunity
Karen Edelblum, Ph.D.
Department of Pathology, Immunology & Laboratory Medicine
Center for Immunity and Inflammation
December 5, 2022
Why is mucosal immunity important?
Where
lymphocytes
are formed and
mature
Where mature
naïve
lymphocytes
are activated
by antigens
1. How do microbial antigens gain access to the immune system?
2. How does your immune system become educated to the
environment?
3. How is the immune system organized to provide the best strategic
defense against invasive microorganisms?
Differences between mucosal and systemic immunity
Mucosal immunity
Systemic immunity
Mucosal immunity provides the first line of defense
•
•
•
Intestine has surface area of 400m 2
¾ of all lymphocytes are located in the intestine
Continuously exposed to antigens and environment
The intestine contains the largest number of
immune cells in the body.
Lymphoid tissue
lumen
muscle
mucosa
Dr. Miyai, Dept of Pathology, UCSD
Gut-associated lymphoid tissue (GALT)
•
intraepithelial
lymphocytes (IEL)
•
lamina propria
lymphocytes
(LPL)
•
Peyer’s patches
•
isolated lymphoid
follicles
•
mesenteric and
caudal lymph
nodes
Lecture Overview
1. Microbial exclusion: production of mucus, IgA, AMPs
2. Antigen entry through M cells, T cell activation and gut homing
3. Mechanisms of mucosal immunosurveillance
– Myeloid cell sampling (GAPs/TEDs)
– Intraepithelial lymphocytes
– Epithelial cells
4. Differences between activation of mucosal and systemic immunity
– Role of commensal bacteria
– Development of mucosal tolerance
– Inflammation of mucosal tissues causes disease, not cure it.
How do we keep microbes out?
epithelial
compartment
basement membrane
lamina propria
Intestinal cell types
Adapted from Gerbe et al., 2011
Mucus production by goblet cells
•
Mucins provide molecular
framework for mucus
•
O-linked oligosaccharides
(glycans)
•
Secrete polymerizing mucins
•
Released from granules
constitutively or following stimuli
after fusion with apical
membrane
Inner and outer mucus layers limit
microbial contact with epithelium.
Mucus prevents direct bacterial contact with the epithelium
Outer mucus layer (home for microbiota) vs. inner mucus layer (pathogens)
• Prevent dehydration of mucosal surfaces
• Physical protection and lubrication
• Diffusion barrier to protect from acid pH
Wenzel et al., PLoS One 2014
Mucosal production of IgA occurs in Peyer’s patches.
• Secretory dimeric IgA is the major
isotype in mucosal secretions. Serum
IgA is monomeric.
• IgA produced by plasma cells located
primarily at mucosal surfaces.
• Selective IgA deficiency is a common
genetic immunodeficiency. Although 8590% of patients are asymptomatic, some
have a tendency to develop recurrent
sinus or GI infections, allergies, or
autoimmune conditions.
Transcytosis of IgA antibody across epithelia is mediated by the
polymeric Ig receptor (pIgR), a specialized transport protein.
Serum: monomer
Secreted form: dimer
The many defensive properties of IgA
Antimicrobial peptides
Mukherjee and Hooper, Immunity 2015
• Amphipathic molecules about 50 amino acids in length
• Broad-spectrum antibiotic activities at low micromolar concentrations
• Produced by phagocytes and epithelium
• AMPs act against many microbes (gram-positive, gram-negative, protozoa,
fungi, some viruses)
Paneth cells
• Transports granules for secretion
• Define composition of SI microbiota
• Sets up a gradient of antimicrobial peptides
• Genetic polymorphisms associated with Crohn’s disease that
result in abnormalities in granule exocytosis and impaired Paneth
cell function
normal allele
risk allele
Cadwell et al., Nature 2008
Salzman et al., 2007
The production of AMPs in the base of the crypt produces a gradient
to minimize interaction between the stem cells and bacteria.
bacteria
Dr. Miyai, Dept of Pathology, UCSD
AMPs
stem cells and Paneth cells
Microbial exclusion
outer mucus layer
inner mucus layer
•
mucus layer
•
IgA
•
antimicrobial
peptides
Lecture Overview
1. Microbial exclusion: production of mucus, IgA, AMPs
2. Antigen entry through M cells, T cell activation and gut homing
3. Mechanisms of mucosal immunosurveillance
– Myeloid cell sampling (GAPs/TEDs)
– Intraepithelial lymphocytes
– Epithelial cells
4. Differences between activation of mucosal and systemic immunity
– Role of commensal bacteria
– Development of mucosal tolerance
– Inflammation of mucosal tissues causes disease, not cure it.
M (microfold) cells are an entry point for microbes.
Uptake and transport of antigens by M cells
immunogen via
epithelium rather than
lymph or blood
Priming of naive T cells and the redistribution of
effector T cells in the intestinal immune system
gut
CCR9
a4b7 integrin
CCR7
L-selectin
GALT
Integrins and chemokines regulate T cell
trafficking to the intestine.
Intestinal mucosal immune compartments
A variety of
effector
lymphocytes
guard healthy
mucosal tissue
in the absence
of infection.
The lamina propria is a thin layer of connective tissue, which lies beneath the
epithelium and together with the epithelium constitutes the mucosa.
.
Lecture Overview
1. Microbial exclusion: production of mucus, IgA, AMPs
2. Antigen entry through M cells, T cell activation and gut homing
3. Mechanisms of mucosal immunosurveillance
– Myeloid cell sampling (GAPs/TEDs)
– Intraepithelial lymphocytes
– Epithelial cells
4. Differences between activation of mucosal and systemic immunity
– Role of commensal bacteria
– Development of mucosal tolerance
– Inflammation of mucosal tissues causes disease, not cure it.
A physical barrier requires active surveillance.
MacPherson and Harris, Nat Rev Immunol 2004
Intestinal myeloid cells and antigen presentation
Flannigan et al., Am J Path 2015
MHCII+ DCs extend dendrites into the intestinal lumen.
Chieppa et al., JEM 2006
CX3CR1+ monocytes extend transepithelial dendrites
(TEDs) into the intestinal lumen to sample luminal antigen.
TEDs increase after Salmonella infection and in response to TLR ligand stimulation
Niess et al. Science 2005
Non-motile CX3CR1+ monocytes transfer antigen to
CD11c+ CD103+ DCs through gap junctions.
Mazzini et al., Immunity 2014
Intestinal myeloid cells and antigen presentation
Sequester microbe
Local antigen presentation
Travel to mesenteric
lymph node
Flannigan et al., Am J Path 2015
CD11c+ CD103+ DCs induce T cell differentiation to promote
oral tolerance or clearance of pathogens.
Steady-state: tolerogenic
– Present innocuous
antigens to induce
Tregs or antigenspecific IgA
– Oral tolerance to dietary
proteins
– Maintains symbiosis
with microbiota
Respond to local
inflammatory cues and
microbial products
MacPherson and Harris, Nat Rev Immunol 2004
Goblet cell associated antigen passages (GAPs)
Miller et al., Mucosal Immunol 2014
DC uptake of luminal antigen from goblet cells
McDole et al., Nature 2012
CD11c+ CD103+ DCs sample luminal contents through GAPs.
•
Soluble antigen delivery
•
Preferentially deliver antigen to
CD103+ LP DCs
CD11c
dextran
nuclei
McDole et al., Nature 2012
GAPs are more common than TEDs in the intestine.
TEDs
GAPs
Knoop et al., Gut Microbes 2017
Knoop et al., Curr Opin Gastroenterol 2013
Effects of luminal sampling at steady-state and
in response to infection/inflammation.
Chang et al., Expt Mol Med 2014
Intraepithelial lymphocytes are phenotypically distinct from other
mucosal immune cells.
•
Intraepithelial lymphocytes (IEL) lie within the
epithelial lining of the gut.
•
IELs are mostly CD8+ T cells.
•
Intracellular cytotoxic granules characteristic of
conventional CD8 T cells (perforin and granzyme).
•
Provide the first line of defense against pathogens.
•
IELs are tissue-resident and do not re-enter
circulation.
IELs provide a rapid response to pathogen, but are tightly
regulated to prevent aberrant tissue destruction.
>
Conventional IELs
Unconventional IELs
Conventional IELs recognize peptides derived from pathogens
presented on MHCI expressed by epithelial cells.
MHCI
IELs kill the infected enterocyte before the infection can spread or
further activate mucosal immunity (lamina propria T cells).
Unconventional IELs recognize stress ligands expressed
on the surface of epithelial cells.
• MIC-A and MIC-B are MHC-like molecules expressed on intestinal
epithelial cells that bind to NKG2D (activating C-type lectin/NK cell
receptor)
• MHC-independent
Epithelial cells are immune cells, too.
MHCI
Express MHC-I and function
as an antigen-presenting cell
Express pattern recognition
receptors to detect
pathogens or their products
Express inflammatory
mediators to recruit and
activate neutrophils,
macrophages &
dendritic cells.
Lecture Overview
1. Microbial exclusion: production of mucus, IgA, AMPs
2. Antigen entry through M cells, T cell activation and gut homing
3. Mechanisms of mucosal immunosurveillance
– Myeloid cell sampling (GAPs/TEDs)
– Intraepithelial lymphocytes
– Epithelial cells
4. Differences between activation of mucosal and systemic immunity
– Role of commensal bacteria
– Development of mucosal tolerance
– Inflammation of mucosal tissues causes disease, not cure it.
• antimicrobial
peptides/IgA
production
can influence
bacterial
populations
• inflammation
-induced
dysbiosis
Commensalism – symbiotic relationship
Commensalism – symbiotic relationship
?
How does the immune response to
good vs. bad antigen differ?
Dietary antigen
Viruses
Parasites
Toxins
Symbiotic relationship with commensal bacteria
•
•
•
•
Thousand different species of bacteria
1012 organisms/ml in colon
Most numerous cells in body by 10-fold
Metabolic function of bacteria
Commensal microorganisms assist in digesting food and
the development of mucosal immunity.
• Bacteria can synthesize
essential metabolites.
• Break down plant fibers in
food into small molecules that
can be used in metabolism,
biosynthesis and
maintenance of intestinal
immune cell populations.
• Interact with the epithelium to
trigger development of GALT.
• Outcompete pathogens for
benefiting from gut resources.
How does the mucosal immune system decide what
constitutes a viable threat?
vs.
Dietary antigens and
commensal bacteria
Pathogens and toxins
Protective immunity and mucosal tolerance are different
outcomes of intestinal exposure to antigen.
Continuous sampling of commensal antigen promotes
a low level anti-inflammatory response.
Mesenteric lymph
nodes form an
additional barrier to
prevent commensals
from entering the
systemic
compartment
Local DCs produce antiinflammatory cytokines
Local regulatory T cells
inhibit inflammation
DCs present antigen
directly to B cells resulting
in IgA production
Antibiotic treatment increases susceptibility to
Clostridium difficile infection.
Mucosal infections are one of the
largest health problems worldwide.
Salmonella enterica serovar Typhimurium, a major cause of food
poisoning, can penetrate the gut epithelial layer by three routes.
Macrophages recruit
neutrophils to help
clear infection
IEL-mediated killing
of infected cell
DCs acquire antigens
from macrophages or
from lamina propria
Phagocytic
mononuclear cells
can sample luminal
antigen/bacteria
DCs travel to MLN via afferent
lymphatics to initiate an adaptive
immune response
Systemic immunity efficiently induces inflammation to clear a pathogen,
but results in tissue damage that requires repair.
>
Mucosal immunity
Systemic immunity
Mucosal immunity functions proactively by maintaining
a constant, low level of protection.
>
Mucosal immunity
Systemic immunity
Inability to properly regulate mucosal immunity results in autoimmune
disease and tissue destruction.
healthy
ulcerative colitis
T cells
Mucosal immunity
Systemic immunity
Mucosal immunity maintains homeostasis and promotes
clearance of infection with minimal tissue injury.
1. Microbial antigens gain access to the immune system
• M cells
• Invade epithelial cells
• Sampled by phagocytic mononuclear cells
2. The immune system is educated by the environment
• Commensal bacteria are symbiotic and contribute to homeostasis
• Continuous sampling of commensal antigen promotes low level anti-inflammatory
response.
• Mucosal tolerance is achieved through development of regulatory T cells and IL10-producing dendritic cells.
3. The immune system is organized to provide the best strategic defense against invasive
microorganisms.
• IELs function as a first line of defense
• Epithelial cells function as antigen-presenting cells.
• Lamina propria dendritic cells traffic antigen to MLN to activate systemic immunity
and recruit antigen-specific T cells to the gut.
• Plasma cells make antigen-specific IgA.
Questions?
karen.edelblum@rutgers.edu
Immunodeficiency Diseases
including AIDS
Tessa Bergsbaken
t.bergsbaken@rutgers.edu
Immunodeficiency Diseases
• Defects in one or more components of the immune
system can lead to serious and often fatal disorders
collectively known as “immunodeficiency diseases”
What is Immunodeficiency?
• A failing of one or more of the body’s defensive
mechanisms resulting in morbidity or mortality
• Any part of the immune system can be deficient
– cells
– proteins
– signaling mechanisms
• Increased susceptibility to specific pathogens, homeostatic
systems in the body will be disrupted by the defect.
• Severity is variable
• Immunodeficiency may be primary or secondary
Primary Immunodeficiencies
• Inherited genetic defects that result in impaired
immune function
• Typically, but not always, manifests in infancy or
childhood
• Clinical expression can be severe or relatively mild
Secondary (acquired) Immunodeficiencies
• The immune deficiency is the result of some other
disease process
–
–
–
–
–
protein-calorie malnutrition
irradiation and chemotherapy for cancer
cancer metastases to bone
immunosuppressive drugs, removal of spleen
infection – HIV
Clinical Features Associated With
Immunodeficiency
• Patients with immunodeficiency diseases are
most often recognized because of an increased
susceptibility to infections
• Chronic/recurrent infections w/o other
explanations
• Infections with organisms of low virulence
• Infections of unusual severity
• Immunodeficiency diseases may also present
with noninfectious manifestations such as
autoimmune diseases
Classification of Primary Immunodeficiencies:
• Cellular deficiencies
• Antibody deficiencies
• Phagocyte disorders
• Complement
deficiencies
Caused by mutations in
genes for specific
proteins in the immune
system (e.g. cytokines,
signaling molecules)
Classification of Primary Immunodeficiencies:
Cellular deficiencies
Antibody deficiencies
Phagocyte disorders
Complement deficiencies
Severe Combined Immunodeficiency
Disease (SCID)
• Defects in lymphoid development
affecting T cells alone or with B cells
& NK cells
• Thymus does not develop; few
circulating T cells.
• Usually presents in infancy.
• Failure to thrive
• Fungal or viral infections – skin,
mouth, and throat lesions
• Pneumonia
• Chronic diarrhea
Causes of SCID
X-SCID
-more frequent in males
Distribution of genetic defects in 170 cases of SCID tracked over 35 years.
[Adapted from R. H. Buckley. 2004, Annual Review of Immunology 22:625.]
Causes of SCID
Almost half of cases are due to
deficiency of the common γ−chain
of the IL-2 receptor – (“boy in the
bubble”)
Causes of SCID
Adenosine deaminase (ADA) and purine nucleoside phosphorylase (PNP)
– eliminate byproducts of DNA metabolism that are toxic to B/T cells.
Causes of SCID
Fig. 13.4, Janeway 10th ed.
Adenosine deaminase (ADA) and purine nucleoside phosphorylase (PNP)
– eliminate byproducts of DNA metabolism that are toxic to B/T cells.
Causes of SCID
Recombination-activating gene 1/2 (RAG1/RAG2)– Loss of recombination
of antigen receptor genes and absence of mature B/T cells.
Causes of SCID
Recombination-activating gene 1/2 (RAG1/RAG2)– Reduction of RAG
function can lead to Omenn syndrome. Loss of B cells, but maintenance
of a small population of autoreactive T cells.
SCID-like deficiencies
ZAP-70 – T cell signal transduction
Relatively normal levels of Ig (IgM) and
CD4+ lymphocytes, but their CD4+ T
cells are nonfunctional, no CD8+ T
cells
TCR
complex
Lck
SCID-like deficiencies
Bare lymphocyte syndrome –
defects in MHC expression
• MHC class II
• Impairment of MHC gene
transcription
• No CD4+ T cells
• MHC class I
• Mutation in TAP genes necessary for Ag loading
onto MHC class I
• Reduced number of CD8
T cells
SCID-like deficiencies
Wiskott-Aldrich syndrome –
mutations in WASp
regulates signal transduction from
the cell surface via the actin
cytoskeleton
F-actin at
the immune
synapse
-reduced T-cell numbers, defective NK-cell
cytotoxicity, and poor antibody responses
-Sinopulmonary infections, eczema, low
platelet count, autoimmunity
SCID-like deficiencies
DiGeorge Syndrome – Deletion of
a large segment of DNA containing
the transcription factor TBX1
-defective development of the
thymus and parathyroid gland.
-haploinsufficiency
-Peripheral T cells are absent or
reduced and do not respond to
polyclonal T cell activators. B cells
may be normal but antibody levels
may be reduced in severely affected
patients.
-Patients are susceptible to
mycobacterial, viral and fungal
infections
Treatment of SCID
-Bone marrow transplantation
-Gene replacement therapy
Antibody deficiencies
Antibody deficiencies
X-linked agammaglobulinemia/XLA mutations or deletions in the gene
encoding B cell tyrosine kinase (Btk),
encoded on X chromosome
• Failure of B cells to mature beyond
the pre-B cell stage in the bone
marrow
• Characterized by:
• Reduced or absent B cells in
the peripheral blood and
lymphoid tissues
• Low levels or absence of
gamma globulin in the blood
• No germinal centers in lymph
nodes
• Maturation, number, and
function of T cells are usually
normal
•Autoimmune diseases develop in
~20% of patients – reason(s) unknown
Mechanisms of XLA
Fig. 13.6, Janeway 10th ed.
Antibody deficiencies
Hyper-IgM syndrome – Defect in
CD40L (on T cells) or CD40 (on B cells
and APC) impairs B cell responses to Tdependent antigens
•
•
•
•
Normal numbers of B cells
Lack of class switching, memory
B cells and germinal centers
are not formed
Deficiency of IgG, IgA, and IgE and
elevated levels of IgM
Production of autoantibodies
Impaired germinal center formation
Fig. 13.8, Janeway 10th ed.
Antibody deficiencies
Combined Variable
Immunodeficiency Disease (CVID)
– Ig deficiency limited to one or more
isotypes
•Clinically and genetically
heterogeneous group of disorders that
are relatively mild
•Decrease in numbers of plasma cells
– therefore reduced serum levels of
IgG, IgA, and often IgM – recurrent
infections (TACl, CD19, ICOS)
• IgA deficiency – most common of all
primary immunodeficiencies (1:600)
Disorders of Phagocytic Cells
ChediakHigashi
syndrome
Macrophage
Disorders of Phagocytic Cells
Disorders of Phagocytic Cells
Leukocyte adhesion deficiency (LAD) – mutations in genes involved
in recruitment of phagocytic cells into the tissue
-LAD-1: CD18 (b2 integrin)
-LAD-2: siayl-Lewisx
-LAD-3: Kindlin-3 – integrin
activation
• Elevated blood neutrophils
• Recurrent bacterial infections – pneumonia, otitis media, peridontitis
Disorders of Phagocytic Cells
Chronic granulomatous disease (CGD) – Defect in
pathway that produces hydrogen peroxide and reactive
products that kill phagocytosed bacteria
• Excessive inflammatory reactions leading to gingivitis,
swollen lymph nodes, and granulomas
CGD
Nitroblue-tetrazolium (NBT) test
normal
Disorders of Phagocytic Cells
Disorders of Phagocytic Cells
(& T cells/NK cells)
Chediak-Higashi Syndrome – Mutation in LYST protein resulting in
defective intracellular trafficking
• Inability to kill bacteria due to impaired phagolysosome fusion
• Impaired degranulation of cytotoxic CD8+ T and NK cells
• Lack of skin, hair, and eye pigment due to impaired melanin granule
trafficking
• Giant granules in blood neutrophils
Disorders of Phagocytic Cells
(& T cells/NK cells)
Chediak-Higashi Syndrome – Mutation in LYST protein resulting in
defective intracellular trafficking
• Inability to kill bacteria due to impaired phagolysosome fusion
• Impaired degranulation of cytotoxic CD8+ T cells
• Lack of skin, hair, and eye pigment due to impaired melanin granule
trafficking
• Giant granules in blood neutrophils
Hemophagocytic lymphohistiocytosis (HLH) – inability to kill pathogens
leads to persistent immune activation
-excessive T cell proliferation
-hyperactivation of tissue macrophages
Evaluation of the Components of the
Human Immune System
• Differential cell counts/flow cytometry analysis
• B cell function
– In vivo: serum Ig levels, specific ab levels
– In vitro: mitogen-induced ab production
• T cell function
– In vivo: skin test
– In vitro: T cell proliferation in response to
mitogens
• Phagocytes: NBT test, intracellular killing of bacteria
• Complement: dilution of serum required to lyse 50%
of antibody-coated red blood cells
Genetic diagnosis of immunodeficiency
• PCR and sequencing
Genetic diagnosis of immunodeficiency
• Newborn SCID screening: T cell receptor excision circles
(TREC) screening
• PCR/sequence to ID known mutations
Therapies for Immunodeficiencies
• Gamma globulin – fraction of blood that contains
Igs. Pooled from 2,000 – 10,000 donors. Contains
Abs to many different antigens.
• Bone marrow transplantation – sibling
• Antibiotics – supportive
• Cytokines
• Gene therapy
CASE STUDY:
A twelve-month old male child with a history of recurrent bacterial infections is
brought to the clinic. A work-up shows that the patient has both B cells and T
cells. Further analysis shows that the patient has high levels of IgM but an
absence of IgG, IgA and IgE in the serum. The patient’s DNA is then
sequenced to look for mutations associated with immune deficiencies. A
mutation in this gene would most likely account for the patient’s condition:
A. BTK
B. RAG1
C. CD40L
D. ZAP-70
E. FoxP3
Secondary (Acquired) Immunodeficiency Diseases
• Due to extrinsic factors leading to defects of immune
function
• Far more common than primary immunodeficiencies
J Allergy Clin Immunol. 2010 Feb;125(2 Suppl 2):S195-203. Epub 2009 Dec 29.
Secondary immunodeficiencies, including HIV infection. Chinen J, Shearer WT.
Infancy is a time of transient
immunodeficiency
Fig. 13.5, Janeway 10th ed.
Aging also results in immunodeficiency
Reduced numbers of naïve T cells are
produced as we age
Singh et. al. Frontiers in Immunol. 2020
Function of existing lymphocytes is also impaired
Xu et. al. Seminars in Immunopathology, 2020
Protein-Calorie Malnutrition
• Worldwide, protein-calorie malnutrition is the most
common cause of immunodeficiency
• Role of minerals and cofactors in transcriptional
regulation of immune maturation
• Specific protein, vitamin and lipid needs of immune
responses
Immunosuppressive Drugs
• Immunosuppressive drugs are often used against
autoimmune diseases and to prevent transplant rejection
• Immunosuppressants work by interfering with the body’s
lymphocytes, cytokines or immune signaling pathways
• Many immunosuppressants are not specific and suppress
many aspects of the immune system 
immunocompromised and vulnerable to a variety of
opportunistic infections
Immunosuppressive Drugs
• Steroids
Fig. 16.25, Janeway 10th ed.
Immunosuppressive Drugs
Biologics with increased specificity
Examples: TNFa/b, TNFR, IL-12/23, IL-17, etc. drugs;
antibodies and small molecule inhibitors
Can still leave the individual more susceptible to specific
pathogens; E.g. TNF-a/TNFR inhibitors: susceptibility to
TB, skin and soft tissue infections, fungal infections
Cancer and Treatment
• Cancer that effects the bone marrow (leukemia and
lymphoma) can impair the generation of immune cells
• Treatments like chemotherapy and irradiation therapy can
enhance the susceptibility to infection through leukopenia,
depression of the immune response, particularly cellmediated immunity.
Splenectomy is Immunosuppressive
• Functions of the spleen:
• Removal of unwanted elements from the blood
• Major secondary organ of the immune system
• Source of hematopoietic cells in cases of
severe anemia.
• Single major clinical manifestation: increased
susceptibility to disseminated infection with
encapsulated bacteria (pneumococcus,
meningococcus, Haemophilus influenzae). This is
probably due to the reduced filtering and antibody
production of the spleen.
Human Immunodeficiency Virus
• HIV leads to acquired immune deficiency syndrome
(AIDS)
– Defects in the immune system at multiple levels (both
cell loss and aberrant activation)
• CD4 T cells
• Monocytes/macrophages
• Dendritic cells
• Antibody defects
• Burn-out – replicative senescence, e.g. with CD8 T
cells
• Immune activation syndrome from improperly “checked”
immune response
Increased susceptibility to infections
HIV-1 Epidemiology USA
Deaths in the USA (1981-2016): 675,000
Living with HIV-1 infection today: 1.2 million people
In 1994, was leading cause of mortality among 25-44 yos
HIV structure
Fig. 13.34, Janeway 10th ed.
HIV Binds to CD4 and Co-receptor
(CXCR4 or CCR5)
Fig. 13.35, Janeway 10th ed.
Life cycle of HIV
Fig. 13.37, Janeway 10th ed.
Activated CD4 T cells are the main cellular
source of HIV production
Fig. 13.35, Janeway 10th ed.
Course of untreated HIV infection
Fig. 13.40, Janeway 10th ed.
The gut is the initial site of depletion of T
cells during HIV infection
Endoscopic and
histologic evidence of
CD4+ T cell depletion
in the Gastrointestinal
(GI) tract during
HIV-1 infection;
massive depletion of
CD4 memory cells
The immune response to HIV
Why are these antibody and T cell responses not sufficient to
control HIV infection?
Fig. 13.41, Janeway 10th ed.
HIV Mutation Occurs
Rapidly
•Low fidelity of RT leads to
frequent mutations
•Escape mutations in response to
selective pressure of the immune
response and/or retroviral therapy
protease inhibitor treatment
Combined anti-retroviral therapy
Current and potential future targets for
combined anti-retroviral therapy
Fig. 13.46, Janeway 10th ed.
New Problems in the Era of Viral
Suppression
• With reasonable compliance, attentive switching of
ART when resistance develops, most individuals can
be virus-suppressed long-term
• Mother-to-child transmission virtually eliminated
• Life expectancy of HIV-infected patient was 13 weeks
post-diagnosis in pre-ART era; now is >20 years.
• Despite viral suppression, still:
– Strong evidence of immune activation, even in “elite
controllers” (people who suppress virus without ART)
– Decreased life expectancy
– Premature aging – diseases associated with aging that
are not be totally explained by toxic drug therapy
(again, even in elite controllers):
• T cell and DC exhaustion and senescence
• Heart disease
• Bone weakness
• Kidney disease
• Major goals in the ART era: What accounts for
chronic immune activation and how can we prevent
or reverse it? How can we bring about a cure?
Vaccine? Immune reconstitution?
What makes vaccination difficult?
-Sequence diversity
-What component of the immune system is protective?
-Viral mutation rate
-Latency in a long lived cell population – CD4+ T cells
-Infection of an important component of the immune system +
immune activation and exhaustion
Resistance to HIV infection – gene therapy
-Homozygous CCR5D32 mutation confers resistance to HIV
infection
-Patient with HIV and leukemia was given a HSCT from a
CCR5D32 donor  HIV below the level of detection in the
absence of treatment (2007)
Questions?