Block 5 Immuno

What are the main differences between innate and adaptive immunity?

Innate (natural, native)

• no memory

• quick response

• low specificity

Adaptive (acquired)

• memory (enhanced by vaccine)

• slow response

• specific

• B and T lymphocytes

Humoral vs cell-mediated immunity components

Humoral = soluble factors in serum and fluids

• most effective against extracellular bacteria

• antibodies

• complement and CRP

Cell-Mediated Immunity = cells that do the work themselves

• effective against intra and extracellular pathogen, etc

• effector cells: phagocytes, granulocytes, and cytotoxic cells

THEY WORK TOGETHER = OPSONIZATION

What is clonal selection?

before infection: each T and B cell has its own receptor shape

antigen selection: antigen fits into receptor and activates it

proliferation: chosen cell copies itself a lot (clones) → each with same receptor as original

Differentiation: each clone takes on 1 of 2 jobs (plasma cell or memory cell)

• plasma cell = effector cell (pump out antibody to fight infection NOW; very short lived)

• Memory cells = stick around for long time. (ready for next time same antigen attacks so response is faster and stronger; think vaccines)

What is opsonization and what contributes to it?

coating a pathogen with molecules so phagocytes can grab and eat it more easily

opsonins = antibody, complement, CRP

What are the cell markers for B cells?

CD19,20,21 (antibody secretion - humoral immunity)

What are the cell markers for T cells? (all, Helpers, Regulatory, Cytotoxic)

all = CD3

helper = & CD4 (cytokine secretion)

Regulatory = & CD4 & CD25 (prevent autoimmunity)

Cytotoxic = & CD8 (kill infected cells, tumors, mismatch grafts)

What are the cell markers for Natural Killer cells?

CD16,56 (kill infected cells, tumors, mismatched graft)

Adaptive immune system overall function and the major cell player

function = build a targeted attack against one specific pathogen and remembers it

major cell players = B & T cells (plasma cells and antibodies)

Granulocytic cell types

neutrophils, basophils, eosinophils, mast cells

phagocytic cell types

neutrophils, monocytes/macrophages, eosinophils

5 resident tissue macrophages

Kupffer cell

microglia

osteoclasts

langerhans cells

synovial A cells

Kupffer cells

help maintain the liver by removal of debris, fighting infection and orchestrating hepatic immune tolerance

microglia

resident macrophage of the CNS

respond to infection, injury, and provide maintenance

osteoclasts

breakdown and resorb old bone tissue

langerhans cells

cells with macrophage and dendritic cell-like characteristics. present antigens to lymphocytes in the skin

synovial A cells

clear debris and help maintain the synovial fluid in joints such as the knee

differential white blood cell counts

leukocytosis = increase WBC (above normal)

leukopenia = decreased WBC

lymphocytosis

high lymphocytes = acute viral infection

neutrophilia

high neutrophils = acute bacterial infection

left shift

neutrophilia due to increased bands/stabs (immature neutrophils)

eosinophilia

high eosinophils = acute worm infection or allergy

Primary vs secondary T-Cell development

primary (central) = thymus

• T cells mature and first express their TCR (before they meet their antigen)

Secondary (peripheral) = lymph nodes, spleen, MALT

• where mature T cells meet and respond to antigen → clonal selection and proliferation

How do T-cells mature in thymus?

1. precursors in subscapular region are double negative (no CD 4 or 8)

2. thymocytes become double positive in the cortex (both CD4 and CD8 present)

3. thymocytes become single positive in the medulla (express one or other but not both CD’s)

**any T cells specific for self are ELIMINATED

What does atrophy of thymus look like and when does it occur in humans?

largest at puberty and then atrophies with age

DiGeorge Syndrome

Thymus (congenital thymic aplasia)

• chromosome 22q11.2 microdeletion

• little to no thymus = few to no T cells → heighten susceptibility to viruses and cancer

• deformed ears, facial anomalies, heart and kidney defects

secondary lymphoid organ: lymph node structure

cortex = B cells

• primary follicles = naive B cells

• secondary = germinal centers with dividing B cells

paracortex = T cells

medulla

• corders = lymphocytes and plasma cells

• sinuses = macrophages, drain into efferent lymphatics

what are germinal centers and what does it means if they aren’t present?

germinal centers are found in the cortex of lymph node

secondary follicles = germinal centers contain dividing B cells

what does asplenia mean?

immunocompromised = more susceptible to encapsulated bacteria

**bonus: spleen is major site of antibody synthesis

splenic white pulp

PALS = T cells surround a central artery

B cell-rich follicles = primary and secondary germinal centers

MALT = Mucosa-associated lymphoid tissue

lymphoid tissue sitting under mucosal surfaces (gut-G, airways-B, urogenital tract-GU) that responds to antigens coming in through those surfaces

• B cells produces secretory IgA

• Peyer’s patches of small intestine

what antibodies may be secreted by structures like Peyer’s patch?

IgA is secreted by B cells (or sIgA) - an antibody that can be secreted onto the surface and survive there

M cells = epithelial cells that mediate transcytosis of antigens from lumen to subepithelial T cells

what happens after an antigen enters the gut?

an antigen enters the gut → M cells carry it to the Peyer’s patch → B cells there make IgA → IgA is secreted into the lumen → it blocks pathogens before they get in

Basic antibody structure

• 2 heavy chains and 2 light chains (held together by disulfide bonds)

  • each chain has variable (out toward antigen) and constant (opp side) region

• Fab end = antigen binding end (grabs the antigen w/ both light and heavy chain V ends)

• Fc end = constant (only heavy chains)

  • recognized by phagocytes, NK cells and granulocytes and Fc receptors)

  • binds complement C1q and CRP

how is the isotype or class determined based on antibody structure?

Which antibody crosses the placenta?

IgG = provides the fetus and newborn with passive protection

(dissipates by age 5-6 months)

IgG functions & how many subclasses?

4 subclasses (1,2,3,4)

• toxin and virus neutralization

• complement activation

• opsonization

• agglutination

• ADCC

what do elevated serum IgG indicate for a person over 6 months?

• past infection or the convalescence phase of a current infection

• prior vaccination

• chronic infection

Primary vs secondary infection immune response. When does IgG dominate?

primary infection = clonal expansion; IgM early & IgG later

secondary infection = memory B cells immediately differentiate into IgG secreting plasma cells

IgM

• major class of the primary immune response

• made of 5 IgG structure with J chain (like a star)

• great agglutinator - 10 binding sites

• elevated levels = acute phase of infection

• only class produced by the fetus

• pentameric, valence of 10

What is the only class of antibody produced by the fetus?

IgM

what does if mean if fetus or newborn has elevated IgM to particular pathogen?

baby is infected by that pathogen

IgA

• 1 & 2

• in seromucous secretions (saliva, colostrum, breast milk, sweat, mucus, etc)

• dimeric secretory IgA contains a J chain

• valance of 4

• secretory component protects sIgA from proteases

• oral and intranasal vaccines induce IgA synthesis

What induces IgA synthesis?

oral and intranasal vaccines induce IgA synthesis

IgE

• similar structure to IgG (monomeric with valance of 2)

• binds FceR on basophils, mast cells, and eosinophils

  • cross linking causes degranulation

• interacts with worms and allergens

• immediate hypersensitivity reactions

SCID

persons who lack functional Rag genes can not make antibodies or TCR molecules

(RAG components generate loops in the DNA which bring together ends of randomly selected V)

How does VDJ recombination lead to genetic recombination?

A randomly selected V, D, or J segment is discarded as two segments come together. Since each B cell does this independently and the combinations multiply there is a lot of variability.

differentiate light chains and heavy chains in VDJ recombination

light = NO D → forming antigen binding site

• one step

• types: kappa and lambda

• Fab only

heavy = VDJ → decision maker

• two steps (D-J then V joins)

• μ, δ, γ, α, ε

• determines antibody class

• Fab + all of Fc

What is AID enzymes main role?

AID enzyme is required for class-switching to IgG, IgA or IgE (noticing when regions aren’t being used)

• reason that once switched from IgM you can’t go back bc H chain was cleaved

• activated when B cell receives T cell help (CD40 on B interacts with CD40L on Th cell)

  • Th cell makes cytokines that determine antibody class synthesized by B cell

What happens when a person is deficient in CD40, CD40L or AID?

they suffer from hyper-IgM syndrome

What is AID’s role in hypermutation and affinity maturation?

AID enzyme → point mutation in V exons of H and L chains

Point mutations occur at a high rate → somatic hypermutation

somatic hypermutation leads to → affinity maturation

which coreceptor binds to each class of MHC for MHC-TCR interactions?

CD4 binds MHC class II on APC and is found on all TH and Treg cells

CD8 binds MHC class I and is found on all Tc cells

What HLA genes correspond to each MHC class?

Major histocompatibility complex (MHC)

class I = HLA-A, B, C

• expressed by all nucleated cells and platelets → NO RBC

• α chain

class II = HLA-DP, DQ, DR

• expression on professional APCs: dendritic cells, macrophages, monocytes, B cells

• α chain + β chain

what is a haplotype?

a group of genes inherited en bloc (as a unit) from a single parent

• humans have 2 (one from mom and one from dad)

components of MHC class I

• α chain (biggest portion)+ β2-microglobulin

• presents to CD8

• HLA-A,B,C

• endogenous antigens come from inside the APC (intracellular viruses, parasites, bacteria)

components of MHC class II

• α chain + β chain

• presented to CD4

• HLA-DP,DQ,DR

• exogenous antigens come from outside the APC (phagocytosed or endocytosed pathogens)

CD3 coreceptor domain and its helps with downstream signaling

• always attached to the TCR on every T cell (marker that tags all T cells)

• made of 6 protein chains

• recognizes the antigen, but can’t send the signal into the cell by itself

  • when binds antigen on MHC

  • tail of CD3 gets phosphorylated → down stream signaling to nucleus

  • results in T cell activation, proliferation, and response to infection

Antigen processing pathway: how antigens are placed on MHC complexes

• endogenous antigens come from inside the APC (intracellular viruses, parasites, bacteria)

  • MHC class I → CD8

• exogenous antigens come from outside the APC (phagocytosed or endocytosed pathogens)

  • MHC class II → CD4

TCR, CD complex all put together

• TCR recognizes the peptide antigen.

• CD4 or CD8 grips the MHC class (II or I) and stabilizes the binding.

• CD3 sends the “activate” signal into the cell.

big picture: Antigen processing pathway: how antigens are placed on MHC complexes

T cells require 2 signals

1. Signal 1: interaction between the TCR and the peptide/MHC complex on the APC

• CD4 or CD8 acts as a co-receptor molecule (this is the right antigen)

1. Signal 2 is provided by multiple co-stimulatory interactions between cell surface molecules on the T cell and the APC (Yes, really activate)

examples of T cell signal 2 (3 of them)

signal transduction: what are Lck and Zap70?

Lck and Zap70 exist and activate the transcription factors: AP-1, NF-AT, and NF-KB

CD4 T cell functions overview (KNOW THIS WHOLE IMAGE)

X-linked immunodysregulation, Polyendocrinopathy, and enteropathy (IPEX)

• mutation in FOXP3 gene = NO Treg cells

• autoimmune disease, allergy, inflammatory bowel disease

• classic triad

  • enteropathy (severe diarrhea)

  • endocrinopathy (type I diabetees mellitus, thyroiditis)

  • dermatitis

• Eosinophilia

• severe atopy with elevated IgE

• increased infections

CD8 T cells overall function & what do they secrete and express?

• kill: infected host cells, tumors, grafts

• secrete:

  • perforin = punches holes in target cell membrane

  • granzymes = activates caspases, induces apoptosis

  • granulysin = kills intracellular bacteria listeria, mycobacterium

• express:

  • FasL = kills target cells expressing Fas by apoptosis (apop does not cause inflam)

What are superantigens?

induce massive cytokine release by T cells and APCs (e.g. macrophages)

• no processing needed

• clamps the outside of Class II MHC to the B chain of the TCR

• induces 20% T cell activation

superantigens (3)

1. TSST-1 : toxic shock syndrome toxin-1 from S. aureus

2. Staphylococcal enterotoxin causing food poisoning

   1. pyrogenic toxins from strep. pyogenes

cytokines associated with superantigens and what do they induce?

TNF and IL-1 → induce:

• low blood pressure

• fever

• DIC (disseminated intravascular coagulation: platelet deposition)

• cardiovascular shock

• cachexia (wasting of muscle and fat)

pleotropism

a cytokine has more than one function

redundancy

multiple cytokines have the same funciton

antagonism

one cytokine blocks the function of another cytokine

synergism

2 or more cytokines enhance each other’s activities

JAK-STAT signaling: know it is associated with cytokine signaling

1. JAK-STAT is how cytokines signal into a cell. Cytokine → receptor → JAK → STAT → nucleus → genes turn on.

2. Too much JAK-STAT signaling leads to autoimmune disease and cancer, so JAK-STAT inhibitors treat them (e.g., rheumatoid arthritis, psoriasis, ulcerative colitis).

3. X-linked SCID: the common gamma chain is broken, so cytokine receptors can’t signal → severe immunodeficiency.