W1P2 Flashcards
(118 cards)
1
Q
What are the main effectors of adaptive immunity
A
B lymphocytes
- B cell receptors (BCR)
- Antibodies
T-lymphocytes
- T cell receptors (TCR)
2
Q
Compare innate vs adaptive immune cells ability to recognize invaders
A
Adaptive, T and B cells:
recognize pathogens via specific receptors that recognize peptides present in the structure of the invader
VS
Innate cells: recognition of patterns rather than specific peptides
3
Q
How does the adaptive cellular immune response get initiated
A
cellular immune response = T cell
A virus, bacteria, fungus or allergen crosses the epithelial barrier
This is a protein that is given in its native form
T cell receptors DO NOT recognize complex proteins
They can only recognize peptides
- They are presented by APCs
4
Q
What are the types of APCs
A
- Monocyte
- Macrophage
- Dendritic cell (DC)
- B-cell
APC process proteins into peptides that can be presented and recognized by T cells
5
Q
What are Antigen Presenting Cells (APCs)
- there are two types
A
All nucleated cells express Major Histocompatibility Complex (MHC) class I and can present antigen usually only when infected Only CD8+ T-cells can recognize class I
Professional APCs express MHC Class II and can pick up antigens, process them and present to CD4+ T cells
Professional APCs express Class II and include: monocytes/macrophages, B cells, dendritic cells, Langerhans cells, Kupfer cells, and astrocytes.
6
Q
What type of cells are langerhans, kupfer and astrocytes
A
Langerhans: resident macrophages of the SKIN
Kupfer: Resident macrophages of the Liver
Astrocytes: are the most numerous cell type within the central nervous system (CNS) and perform a variety of tasks, from axon guidance and synaptic support, to the control of the blood brain barrier and blood flow.
All of these are further examples of PROFESSIONAL APCs. Thus they all have MHCII receptors
7
Q
Dendritic cells: what receptors do they have, what can they recognize
A
Dendritic cells have a large number of innate immune receptors
- eg Toll-like receptors (TLRs 1-11)
- Can also recognize antibody coated antigens
- Complement coated antigens
8
Q
Dendritic Cells, what are their functions?
A
- Engulf and process Ag, and process them for T cell by digestion into peptides on MCHII
- Releases cytokines (IL-12)
- Migrate to areas that have large T cell populations e.g. lymph nodes
- Express co-stimulatory molecules
9
Q
T lymphocytes
- where can they be found
- where were they developed
A
Found: Circulating cells that populate the blood and lymph nodes, make up 70-85% of peripheral lymphocytes in normal individuals
- Develop in the Thymus
- We are all born with a limited ‘repertoire’ of antigens that our T cells do or do not recognize
Exposure helps mature and refine the responses!!
10
Q
How do T cells work?
- What must it have to recognize an antigen
A
For recognition, T cell must have:
- a receptor that can recognize a specific peptide (TCR) which would interact with the MCH2
- a signaling complex (CD3)
- a CD4 or 8 molecule
11
Q
How does a T cell know they are meeting the right APC?
A
The immune system has developed a system to ensure that T cells only respond to cells from the “Self”
These are known as Major Histocompatibility antigens
Biometrics!
12
Q
What are the 3 roles for T cells?
A
- Fight intracellular infections
- CD8 cytotoxic T-cells - Assist other cells by activating them and helping them multiply or differentiate
- CD4+ effector T-cells: Th1, Th2, Th9, Th17 - Provide signals that inhibit or slow down inflammatory responses
- Regulatory T-cells (CD4+Foxp3+)
13
Q
Which are the effector T cells?
A
Effector T cells are CD4+ and have various functions:
- Supply cytokines to monocytes to help them fight intracellular organisms. These are designated T helper 1 (Th1).
- They also can supply cytokines to B cells to direct specific antibody responses. These are designated T helper 2 or Th2.
- Supply cytokines that activate phagocytes and other innate immune cells; designated T-helper 17 (Th17)
- Regulate all cell activites via IL-10, TGF-b or cell-cell contact: Regulatory T-cells (Treg)
14
Q
T cell Activation
A
Once a naïve T cell is stimulated,
it’s surface architecture changes
When a T cell recognizes a peptide, its surface changes, it up-regulates:
- cytokine receptors eg IL2R
- adhesion molecules eg CD28
- chemokine receptors eg CCR3,4,5
These help amplify the T cell multiplication
the cytokines;
- help T cell multiply
- tell other cell in the environment, what to do
15
Q
T cell proliferation depends on…
A
If T cells are not able to produce or recognize cytokines
- They cannot grow or multiply
- eg IL-2 receptor common gamma chain deficiency
- IL-7Ra deficiency
They cannot defend against specific pathogens
- IFN-γ or IL-12 and severe mycobacterial infection
16
Q
What are the clones of T cells and what are their functions
A
Effector T cells: cells that will stimulate or attack other cells in the environment (CD4 derivatives: Th1, Th2, Th17, Treg)
- This will magnify the response.
Memory T cells: small clone of antigen recognizing cells for future recognition of the same antigen
17
Q
Th1
- which cytokines
A
Intracellular organisms
IFN-γ, IL-12, IL-18
Supply cytokines to monocytes to help them fight intracellular organisms. These are designated T helper 1 (Th1).
18
Q
Th2
- Which cytokines
A
Antibody production, parasite defense, allergy
IL-4, IL-5, IL-13
They also can supply cytokines to B cells to direct specific antibody responses. These are designated T helper 2 or Th2.
19
Q
Th17
- which cytokines
A
Supply cytokines that activate phagocytes and other innate immune cells; designated T-helper 17 (Th17)
Antibacterial, antifungal
IL-17, IL-22
20
Q
T reg
- which cytokines
A
Immune response regulation: IL-10, TGF-β
Regulate all cell activites via IL-10, TGF-b or cell-cell contact: Regulatory T-cells (Treg)
21
Q
CD8 T cells, roles?
A
T lymphocytes directly fight viral and fungal infections. These are cytotoxic T cells (designated by the molecule CD8
- Recognition of infected cells Viral immunity - Production of Pro-apoptotic Proteins Perforin and Granzyme - Can produce pro-inflammatory cytokines e.g. IFN−γ
and has a T reg: Immune response regulation: IL-10, TGF-β
22
Q
Cytotoxicity
A
Mediated by CD8
CD8+ cells recognize antigen presented on MHC I by infected or diseased cell
Induces apoptosis by
- FAS-FASL interaction
- production of TNF
- injection of toxic substances
- Peforins and granzyme.
23
Q
What happens if T cells do not work?
A
- Cell mediated immunity
- Severe viral infections
- Severe bacterial infections - Humoral Immunity
- B cells can’t make antibodies - Other cells can’t get activated
- Monocytes, macrophages, eosinophils - Congenital
- Severe Combined Immune Deficiency
- Defective cytokine receptor (X-linked SCID)
- Defective receptor signaling (JAK3, ZAP70 deficiencies)
- Absent T cells (Adenosine deaminase deficiency)
- Many others - Acquired
- HIV disease
24
Q
How do you measure if T-Cells have memory for a virus like SARS-COV2
A
25
B-Cells
- what percentage of circulating lymphocytes do they make up
What are their primary functions
- The producers of antibody
- So named because they come from “bone marrow” or, in chickens, from the “Bursa of Fabricus”
- They make up 5-15% of circulating lymphocytes.
- Each progenitor B cell is capable of coding for a distinct antigen.
Primary Functions:
- Recognize foreign substances (antigens) via B-cell receptors (BCR) on their surface that look like antibody molecules (surface Ig or sIg)
- Present Antigens to T-cells (they are professional APCs)
- Secrete Antibodies!!
- Produce Cytokines
26
What is the basic structure of a B cell
B cell receptor (BCR)
MCH class II [professional APC]
CD19, CD20
27
B cell maturation
- B cells arise in bone marrow from stem cells
- They are released into circulation after several maturation steps
- Immature or naïve B cells are released into circulation at a stage when most cells can secrete IgM and have a BCR on their surface
- B cells home to areas of antigen dependent maturation (e.g.) lymph nodes, spleen, to interact with T cells and specialized Follicular Dendritic Cells
28
How do B cells recognize antigens
- B cells recognize three dimensional structures of antigens
- Because they are antigen presenting cells, they internalize antigens and process them into peptides
- B cells trap antigen in a different form than they present them
- T-cells are presented these peptides via MHC II to the TCR
29
When a B cell presents an antigen to a T cell, what does it lead to?
It leads to production of Ig/ antibodies
co stimulus: CD80/86 on B cell stimulated CD28 on T cell
then MHC2 on B cell with CD3/CD4/8 on T cell
30
Key Messages,
| relationship between antibodies, antigens, B cells, the isotopes...
One antigen, many potential antibodies
BUT: One B-cell, one antibody
One antibody, multiple isotypes
31
How to make a better antibody?
- In lymph nodes, antigen specific B cells undergo affinity maturation
- Antibodies of increased affinity for better immune responses are produced through mutation of their BCR genetic program (somatic mutation)
- Only those able to interact strongly with antigen will mature (many are called, few are chosen!)
32
Primary vs Secondary Follicle
Primary Follicle: Naïve B-cells who had not seen antigen; cells can mature to Memory B-cells or Plasma Cells
Secondary Follicle: Memory B-cells already present, more rapid response, more memory cells, more plasma cells
33
B cell facial features of a Memory Cell
- Memory cells: responds rapidly to antigens, matures rapidly
BCR: same structure as an antibody molecule; it recognizes presented antigens. Short signal transduction chain, coupled to two intracellular signaling molecules Igα and Igβ
CD19,CD20: common B cell surface adhesion molecules; important in allowing a cell to be activated.
MHC class II means that B cells can be professional antigen presenting cells to T cells.
Fc receptors: many cells have receptors for the "constant region" of antibody molecules. B cells have a subclass called FcγRIIb - unique because it inhibits or diminishes cell activation when it is occupied.
CD40: strengthens T cell - B cell interaction.
CD28/B7.1: strengthens T cell - B cell interaction.
34
B cell facial features of Plasma Cells
Plasma Cells: most mature subtype of B cell, produces and stores copious amount of Ig and cytokines
- CD38
- CD138
35
Antibodies
- made by
- where are they found
- types
- regions
- Made by B cells
- Circulates
- Recognizes specific substances on its “variable region”
- Taken up by phagocytic cells via its “constant region”
- IgG, IgA, IgM, IgE and their subclasses
36
Antibody structure
- Made up of proteins known as immunoglobulins.
- Two pairs of chains: heavy chain and light chain, linked together by different bonds.
constant region: heavy chain (legs), Fc fragment
variable region: light chain (arms), antigen binding site
37
What are the types of Heavy and Light Chains
```
5 different heavy chains
µ makes IgM,
α makes IgA,
γ makes IgG,
ε makes IgE,
δ makes IgD.
```
2 different light chains:
Kappa κ
Lambda λ
38
Fc portion vs antigen binding cite
Fc:
The COOH ends of the heavy chains, plus a small part of the light chain, pairs up into the constant region. All molecules of a particular Isotype have similar constant regions.
Antigen binding site:
The NH2 ends heavy and light chains pair up to form the variable region of an antibody molecule. In this area is the specific antigen binding region - the unique portion of the molecule.
39
Consequences of B cell dysfunction
- No antibodies
- Moderate to severe bacterial infections
- Encapsulated organisms (pnemococcus,
- moraxella, hemophilus influenza)
- Mycoplasma and species
- Pneumonia, sinusitis, sepsis, meningitis,
- Osteomyelitis
40
Humoral Immune Disorders
No B cells
- X linked agammaglobulinemia
Missing cell communication adhesion molecules
- Hyper IgM syndrome (non functioning CD40L on T cells)
Other poor B or T cell function
- combined immune deficiency
- common variable immune deficiency
41
IgM
- 10% of circulating Ig's
- Circulates as a pentamer, linked by disulphide
- bonds and a J-chain
- 1st antibody made ("defaut setting for B cells")
- Excellent at complement fixation
- No Fcµ receptors so poor at opsonization
- Good at neutralization
This is the PRIMARY response antibody
- Primary response is IgM, think M for mother
- Subsequent antigen challenges leads to switch
- from IgM to IgG, A or E via gene rearrangement
cytokine and environment dependent
42
IgG
- percentage of circulating ABs
- what are the 4 subclasses
- unique feature
- 75% of all circulating antibodies
- Main Ig produced in secondary antibody responses
- 4 subclasses IgG1 (70%), IgG2 (15-20%), IgG3 (5-10%), IgG4 (1-5%)
- Only antibody that crosses the placenta
- Most pass actively in 3rd trimester
43
IgG properties
- half life
- other downstream functions
- which surfaces are they found on?
- ½ life app. 21 days: produced after age 3-4 months
- Good at fixing complement (IgG3 > IgG1 > IgG2 >> IgG4
- Excellent opsonization (Fcγ receptors)
- Some IgG at mucosal surfaces
44
IgA
- 15-20% of circulating Ig
- Lines mucosal surface : excellent 1st line of defense
- Exists as a dimer (2 molecules + J chain)
- Secretory piece added: protection from proteolysis
- Excellent at neutralization, but fair at complement activation
- Fair at opsonization
- Most common immune deficiency (1:700)
45
IgE
- Very low amounts in serum
- Most IgE is bound to mast cells + basophils (FcεR)
- Key Ig in parasite defence
- Responsible for allergy and anaphylaxis
- Some complement activation (alternate pathway)
- More in later lectures
46
IgD
Little circulating
No clear role in host defense
Important marker of B cell maturation
47
What is necessary to elicit a strong antibody response
- Antigen
- T cells for direct contact (usually TH2 cells)
- Soluble cytokines (eg) IL4 + IL13, INF-γ or IL10)
- Certain adhesion molecules esp CD40
48
```
Cytokines and Antibody Switch
which produce:
IgG
IgA
IgE
which IL augments all isotypes:
which drives plasma cell development?
```
```
IgG1, IgG2 and IgG3: IFN-g or IL-4
IgA and IgG4: IL-10 or TGF-b
IgE: IL-4 or IL-13, IL-9
All Isotypes are augmented by IL-21
Plasma cell development is also driven by IL-6
```
49
Primary Immune response
Happens from Naive B cells
starts with IgM, which can become IgA and IgG
which become plasma and memory cells
requires 21 days
50
Secondary response B cells response
from pre-existing memory cells
happens within 3-5 days
51
Why do antibodies appear to wane?
Humoral Immune Response
Kinetics of humoral immune response after infection: comprising two waves of antibodies. Wave 1 antibodies are produced by rapidly expanding, short-lived plasma cells aimed at populating the systemic circulation with antibodies that provide some level of defense as more affinity-matured antibodies evolve. Wave 2 antibodies are generated by long-lived plasma cells that, although less common, generate potent high-affinity antibodies that typically confer long-lived immunity. Because the decay kinetics differ considerably between wave 1 and wave 2 antibodies, sampling time can dramatically affect calculations of the rate of decay: rapid decay would be observed at the end of wave 1, whereas slower decay would be observed in wave 2
52
What is the role of antibodies in defense
1. Opsonization - the coating of an organism by an antibody, allowing it to be taken up by a neutrophil or macrophage via its Fc receptor. This increases the efficiency of phagocytosis and its subsequent killing.
2. Complement Activation - complement binds to specific regions on Ig molecules, allowing the complement cascade to be activated. This leads to more efficient phagocytosis as well as cell killing.
3. Neutralization: antibody binding a substance before it can adhere to a cell and infect it.
4. Antibody Dependent Cellular Cytotoxicity: antibodies coating pathogens (usually viruses) are taken up via FcγR111 on NK cells, leading to the killing of the cells the viruses had infected. The viruses must be presented by MHCI.
53
In what conditions do antibodies promote neutralization vs opsonization vs complement activation?
Bacterial toxins: cell with receptors for toxins
leads to NEUTRALIZATION of toxin to then be ingested by macrophages.
Bacteria in extracellular space: opsonization to be ingested by macrophages.
Bacteria in plasma: Compliment activation
leadings to lysis and ingestion
54
Monoclonal Therapy
Anti-CD20 (Rutuximab)
- Removes all B cells
- Useful in lymphoma
- Highly used in autoimmune diseases
55
Signs and symptoms of Milk Protein Allergy in infants
regurgitating milk after meals
becoming more fussy and irritable (notable behaviour change)
excessive crying
refusal to bleed
also very common:
stools become more frequent and watery
- notice flecks of blood in stool
- could have normal wt gain
56
Epidemiology of MPA
MPA = milk protein allergy
affecting up to 15% of healthy infants
57
What is the most common type of milk protein allergy
cow's milk protein
- incidence as high as 2.1% of all infants
is usually caused by bovine milk, but theoretical cross-reactivity with protein from goat, buffalo, or ewe milk
58
What percentage of children wwith cow milk protein allergy will have allergy to beef? what is the mechanism of this?
13-20% will also be allergic to beef
this is through the cross-sensitization
59
Mechanism of Milk Protein Allergy, what are the two types?
There is IgE mediated and NON IgE mediated
60
What is the mechanism of IgE mediated MPA?
```
IgE mediated (type 1 hypersensitivity)
- Antigen binds to IgE antibody that is bound to mast cells (already sensitized)
```
- Cross-linking of two IgE AB by antigen causes degranulation of mast cell and release of histamine -> inflammatory mediator -> immediate allergic response
61
What is the mechanism of NON IgE mediated MPA?
complex and multifactorial. Could be either:
a. Immune complexes of IgA and IgG bound to milk antigen (T3 hypersensitivity)
b. direct T cell stimulation by the milk protein antigen (T4 hypersensitivity)
These interactions lead to cytokine release and increased production of AB that recognize the offending milk protein antigen
causes a delayed and complex immune-mediated inflammatory cascade.
62
What is the main distinguishing factors of the two types of MPA?
There is a lot of overlap in symptom profile of MPA that is IgE and non- IgE mediated
Distinction between the two is important
IgE-mediated MPA is associated with a higher risk of other food allergies, eczema, and emergence of asthma later in life
63
What is Food Protein Induced Allergic Protocolitis (FPIAP)
- What are the common triggers?
Common cause of rectal bleeding in an otherwise healthy infant
Caused by non-IgE mediated inflammation of the distal colon in response to a dietary trigger
```
Common triggers:
Cow’s milk
Egg
Soy milk
Corn
Multiple (>2)
```
64
What is the clinical presentation of IgE mediated MPA?
urticaria, pruritic, wheeze, cough
65
Clinical presentation of NON IgE mediated MPA
will present with gastrointestinal manifestations:
| colitis: blood and/or mucous-streaked stool
66
Can both types of MPA co-exist?
YES
Clinically, the two diseases can co-exist - diagnosis is not always straightforward
67
Diagnosing MPA what should you look out for in the physical exam?
MPA is a clinical diagnosis*
it is based on history and physical exam:
wt gain
anal fissuring
hemoccult testing of stool if blood is not visible
Laboratory Testing: Not necessary in well- appearing infants with typical symptoms
if you want lab tests:
- low serum albumin: suggests enteropathy
- high CRP, WBC: indicate inflammatory response
Skin testing/blood testing for serum IgE antibodies**** to determine if it is IgE mediated MPA
68
What are the DDX in MPA?
- Anal fissure - ask about stool consistency on history
- Intussusception
- Acquired enteric infection
- Meckel’s diverticulum (presentation in <6 month old is rare, however)
Necrotizing enterocolitis (NEC) - there is usually a history of prematurity in these babies
69
what is the treatment of MPA
eliminate the offending protein/allergen
in breastfeeding: change mother's diet in a nutritional and sustainable way.
sequential elimination:
- cow's milk protein
- bovine protein (beef)
- if symptoms are not optimized, eliminate soy protein
70
How long will it take to see therapeutic effects of MPA treatment?
dietary elimination will take 7 days for washout period from maternal diet
71
How do you treat MPA in a formula feed infant?
| - what are causes of compliance issues?
Their formula must be optimized:
Extensively Hydrolyzed Formulas: incorporate hydrolysates of casein or whey derived from cow's milk
Amino acid based formulas: created constituent amino acids
Compliance issues:
- due to TERRIBLE taste
- the more hydrolyzed the formula, the worse the taste.
substituting soy based formula is NOT recommended.
72
Reintroduction of Milk Protein
The timing of reintroduction of milk protein will depend on if the child has an IgE or non-IgE mediated process
Non IgE mediated MPA can trial reintroduction at 12 months
IgE mediated MPA guide reintro based on skin testing and consultation with their allergist
73
What is the nomenclature for the types of MPA
IgE mediated: allergies
NON IgE mediated: intolerances or hypersensitivities
better to use proper term. negative understanding of "allergy" that makes it scary for parents to reintroduce offending food
avoidance diets can contribute to the development of allergy in this population.
74
What is the prognosis of NON IgE MPA?
excellent
nearly ALL infants are able to toelrate their allergen at 1 year of age
the progression to persistent food allergy, chronic colitis, or IBD is extremely rare
75
What are the two types of Immune organs/ lymphoids?
Primary (central) lymphoid organs
- Bone marrow
- Thymus
Secondary (or peripheral) lymphoid organs
- Lymph nodes
- Spleen
- Mucosa-associated lymphoid tissue (MALT), including Waldeyer ring (tonsils, adenoids…), Peyer patches in ileum…
76
Describe the 3P's related to Bone Marrow as the origin of lymphoid lineage
- what is a key marker here
- Contains Pluripotential hematopoietic stem cells (CD34+)
- Give rise to Progenitor hematopoietic cells including of the lymphoid lineage
- Progenitor cells become B- or T- blasts (also called “Precursor”) that gradually differentiate into mature, functional and easily recognizable cell types
77
Where is bone marrow found in adults?
found mostly in skull, ribs, sternum, vertebrae, pelvis, proximal femur
78
What are the B-blasts markers?
B-lymphoblasts ≈ hematogones
Normally very few in marrow
Are CD19+, TdT+, CD34+, CD10+ (i.e., B-blasts)
79
Which gene is involved in the B and T cells having a repertoire of Igs and others T cells
The VDJ gene
| rearrangement which is what generates repertoire of Igs
80
What is different about the mature B cells in the bone marrow?
Mature into NAIVE but mature b cells (not yet exposed to antigens)
- they are CD20 positive and lose "blast" status
Many then migrate to secondary = peripheral lymphoid organs via the blood stream.
- a few remain in marrow and blood
81
Thymus
at birth vs adulthood
what is the main process that occurs here?
This is another primary central lymphoid site for T cells to mature. thymic university.
This is a bilobed anterior mediastinal organ, derived from 3rd pair pharyngeal pouches
At birth, large, very active in T cell production, until puberty, then
Gradual involution, largely replaced by adipose tissue in adult but still partly active.
82
What is the anatomical structure of the thymus?
You have LOBULES, separated by SEPTUM
within each lobule you have the CORTEX with the MEDULLA in the middle
Everything is surrounded by the capsule which is the most superficial layer.
in the opening is the perivascular space
83
What cells are found in the Cortex of Thymus
Isolated compartment with the following types of cells:
a. cortical epithelial cells form cortico-medullary barrier. These cells function as APCs, secreting cytokines.
b. Macrophages
are professional APCs
they function in phagocytosis of apoptotic cells
c. T-lymphoblasts = thymocytes = precursor T cells, they are TdT positive.
84
What cells are found in the Medulla of the Thymus
contains small MATURE T lymphocytes, TdT NEGATIVE
- epithelial cells, smaller spindle-shaped, forming Hassall's corpuscles*
- small population of mature B cells, CD20 POSITIVE associated with epithelial cells, that MAY play a role in T cell differentiation.
85
What are the functional aspects of the Cortex of the Thymus
As in bone marrow for B-cells, T-cells undergo VDJ rearrangement, resulting in
T-lymphoblasts = thymocytes = precursor T-cells, TdT+, initially double negative for CD4 and CD8, then double positive (CD4+/CD8+)
Positive selection allows survival only of T-cells with functional T-cell receptors (TCRs) recognizing MHC class I and class II molecules
86
Where would you find Hassall Corpuscles
In the Medulla of the Thymus
87
Functional aspects of the Medulla and peripheral perivascular space of the Thymus
Medulla: negative selection allows survival only of T-cells that do not tightly bind self-antigens
Peripheral perivascular space: contains mature naïve T-lymphocytes, CD4+ or CD8+ that travel to lymph nodes, other peripheral lymphoid sites and blood
88
Lymph Nodes
- How many lymph nodes are in the body?
- Function
- What do they contain, how did they get there?
- what are they an important source of?
- supported by a framework of _____ cells
- Number 400-450 in body, max. diameter 1 cm (1.5 cm for inguinal nodes), often along major vascular routes
- Drain and filter lymph from various organs, protecting against organisms, tumor cells and other foreign invaders
- Naïve B- and T-cells arrive by blood stream from bone marrow and thymus respectively, and enter the lymph node via high endothelial venules (HEVs)
- Are an important source of Abs (mostly IgG and IgM) produced by plasma cells in medulla
- Supported by a framework of fibroblastic reticular cells
89
What are the anatomical layers of a lymph node from out to in?
Cortex
a. lymphatic nodule
b. Germinal Center (capillary where HEV delivers cells)
c. Mantle zone
Paracortex
a. between cortex and mandible
Medulla:
a. Medullary sinus
b. Medullary cord
90
Lymph Node structure: Cortex
primarily B cells
- In quiescent lymph node (no antigenic stimulation), naïve (mantle) B-cells await Ags in 1o B-follicles or nodules
- With Ag stimulation, form germinal centers
Cells in follicles/germinal centers
B-lymphocytes in various stages of activation: centrocytes and centroblasts
Helper CD4+ T-cells
Follicular dendritic cells (APCs)
Macrophages, for phagocytosis of apoptotic cells
91
Where would you find naive mature B cells?
in the MANTLE cells of lymph nodes
these are cells in the cortex
you'd use CD20 markers
92
Where would you find T cells and IDCs in a lymph node?
in the paracortex
CD3 positive
93
What is in the Medulla of Lymph nodes?
Medullary cords: B and T lymphocytes, plasma cells
Medullary sinuses, lined by discontinuous endothelial cells allowing free trade and final filtering of lymph, and containing numerous macrophages.
94
Journey of lymph in lymph node
1. Afferent lymphatics: bring Ags, bugs, tumor cells
2. Subcapsular sinus: Conduit, distribution
3. Cortical Sinuses: Exposure B, T cells to Ags
4. Medullary Sinuses: Add Abs from plasma cells
5. Efferent Lymphatics: exit to other more central nodes, then blood
95
B cell response to first arrival of antigens
Early primary immune response
Occurs outside the germinal center, in paracortex
T-cell-independent activation of naïve B-cells to proliferating B-immunoblasts → short-lived IgM-secreting plasma cells, but no memory cells
Abs secreted have lower affinity for Ag than those from 2o response
Some IgM+ B-immunoblasts migrate to primary B-follicle to initiate the secondary response
96
Secondary B cell immune response upon arrival of antigens
Later (3-7 days), T-cell-dependent activation of naïve B-cells to proliferating B-centroblasts → centrocytes → immunoblasts → IgG-secreting long-lived plasma cells and memory cells (latter in marginal zone then medulla)
Occurs mostly inside the germinal center (GC)
Produces Abs with high affinity for the Ag
Various cytokines, BCL6, CD10 (both GC markers) required for this to occur
In normal or reactive GC, the anti-apoptotic protein BCL2 is downregulated
97
Which cytokines are required for secondary immune response?
BCL6 and CD10, which are both germinal center markers are required for the T cell dependent activation of naive B cells
98
What is the lymph node follicle?
It includes the germinal center and the mantle zone in the CORTEX
99
What is the anatomy of a normal germinal center?
It is POLARIZED
Naive mantle cells surround Light Zone of GC, and if you go deeper you get a DARK ZONE of GC (starry sky pattern)
100
What are the 4 Key steps in germinal center reaction?
1. Proliferation
2. Somatic hypermutation of Ig V region genes --> increase affinity of Ab for Ag
3. Selection
4. Differentiation
101
Proliferation stage of GC reaction
Proliferation:
- Ag stimulated B-blasts -> centroblasts in dark zone
- cycle rapidly (6-12 hrs)
- Inactivate BCL2 anti-apoptotic gene --> apoptosis is facilitated*
- Tingible-body macrophages eat apoptotic cells (starry sky)
102
Somatic hypermutation of IgV region genes phase
This is the second stage of germinal center reaction
purpose is to INCREASE the affinity of Ab for Ag
103
Selection Phase
This is the third stage in germinal center reaction
centroblasts mature -> centrocytes -> light zone GC
Ig heave chain class switch: IgM -> IgG or IgA
centrocytes with high affinity to Ag bind to it, interact with GC T cells, and rescued from apoptosis
centrocytes with low affinity undergo apoptosis
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Differentiation stage of Germinal Center reaction
Into memory cells + plasma cells
- with inactivation of BCL6 gene, and interaction with T cells
- B- immunoblasts, plasma cells and memory cells are in MARGINAL ZONE, outside of GC
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Plasma Cells, the different types
| - what do they secrete, be specific
IgM-secreting plasma cells short lived (1o response)
IgA or IgG-secreting plasma cells long lived (2o response)
Travel to medulla of lymph node, bone marrow, other sites
Each plasma cell secretes either kappa or lambda light chain and only one heavy chain (IgG, IgA…)
Plasma cells in a lymph node are polyclonal, i.e., mix of κ− and λ-secreting
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T cell response to antigen arrival
- where
- what receptors are involved
Occurs in paracortex of lymph nodes, periarteriolar sheath of spleen, extranodal sites
Ag presented to T-cells by APCs
CD4 or CD8 on T-cells bind to MHC class II or class I, respectively, on APCs
Mature T-cell → T-immunoblast →
Effector CD4+ helper cells
Effector CD8+ cytotoxic cells
Memory T-cells
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What are the functions of the spllen
filterns blood
destroys old RBCs using macrophages
produced Abs and effector T cells
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What is splenic parenchyma consist of
White pulp (20%)
- lymphoid nodules
- periarteriolar lymphoid sheaths (PALS)
Red pulp (80%)
- Sinusoids, blood filled
- Splenic cords of billroth
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Splenic B- follicle and germinal center ANATOMY
similarily has a germinal center with a mantle zone around it which is surrounded by a marginal zone
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Muscosa- associated lymphoid tissue (MALT)
What are their different locations?
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Waldeyer ring (naso/oropharynx, tonsils, adenoids…)
Along GI tract, mostly small and large intestines (appendix, Peyer patches in ileum), sometimes tracheo-bronchial tree
May be “acquired” MALT in stomach, other sites, with chronic inflammation
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MALT Functions
Defense of internal passages against foreign invaders, Ags…
Harbors about 70% of body’s immune cells
Bacteria and other microbes in oral cavity, gut etc., activate the 2o immune response, both B- and T-cell
The appendix, in addition to a lymphoid organ, may serve as a reservoir of beneficial bacteria to replenish the depletion following diarrheal diseases
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Provide a summary
B cell differentiation:
Bone Marrow: Precursor B cells
Interfollicular area: Naive B cells meet antigen leads to primary response, short lived IgM production
Follicular area: They go to germinal center where they become centrocytes ready for secondary response. interaction between T and B cells?
Perifollicular/ Marginal area: you have differentiation into plasma and memory cells
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T cell differentiation Summary
Central lymphoid tissue/bone marrow: progenitor T cell goes to
Thymus: becomes CD4 or CD8 as NAIVE
Peripheral lymphoid tissue: they meet an antigen and become T blasts which then can differentiate into memory vs effector T cells!
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Comparing maturation of B vs T cells
Bone marrow B-lymphoblasts mature into naïve B-cells that go to peripheral lymphoid organs
T-lymphoblasts go directly to thymus and mature there, then to peripheral lymphoid organs
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What are the different species of blast?
B and T lymphoblasts: precursors in marrow and thymus
Centroblasts: in the Germinal Center, mature B cells
B and T immunoblasts: after exposure to the Ag, give rise to plasma cells and B-memory cells and T-memory cells, respectively
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What are the T cell markers?
CD3 very specific
| CD4: helper T-cells; CD8: cytotoxic T-cells
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What are the markers for:
anti-apoptotic:
Follicular center cells:
Plasma cells:
BCL2: anti-apoptotic
BCL6, CD10: follicular center cells (CD10 also in lymphoblasts)
CD138, κ, λ light chains: plasma cells
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What IL do DC release?
IL12 once they present an antigen
