Immuno Week 2 SI

Formation of Ig heavy chain variable domain

Variable (V); Diversity (D); Joining (J)

Formation of Ig light chain variable domain

Variable (V); Joining (J)

formation of TCR beta chain

variable domains → Variable (V); Diversity (D); Joining (J)

formation of TCR alpha chain

variable domains → Variable (V); Joining (J)

Ig κ light and λ light chain constant domains encoded by

a single exon;

TCR α chain constant domain encoded by

a single exon

When a cell decides to become a B cell, describe the process

When a cell decides to become a B cell, it wants to make IgM to put on its surface. It rearranges one of its D region gene segments & joins with a J segment. Everything in between the D and J segments will be clipped out by RAG1/2, and the D and J genes will be ligated to each other by Artemis & ligase. THIS IS IRREVERSIBLE. The same thing happens with a V segment; V segment will be ligated next to the D and J using Artemis & ligase, and RAG1/2 will clip out the material in between. THIS IS IRREVERSIBLE.

VDJ Recombination: RAG1/2

make a hairpin loop between a V and D segment

VDJ Recombination: Artemis/DNA-PKcs

cuts the hairpin loops on V and D segments, allowing them to join together (hairpin resolution) with help of ligases.

VDJ Recombination: TdT

adds nucleotides

VDJ Recombination: NHEJ proteins

ligate the segments

VDJ Recombination: allows for

immune system diversity

STARRED: Without RAG1 and RAG2

lymphocytes can’t develop → Severe combined immunodeficiency, SCID (no T or B cells).

B-cell Development: heavy chain vs light chain

Heavy chain - VDJ gene recombination. Light chain - VJ gene recombination

B-cell Development: enzyme responsible for gene recombination is

RAG

B-cell Development: Terminal deoxyribonucleotidyl transferase (tdt) increases diversity by

adding random nucleotides during rejoining

B cell differentiation plot

Pre-B Cell Receptor → BCR

Heavy chain is rearranged before the light chain. Surrogate light chain on Pre B-cell = Vpre-B and lambda 5

Bruton’s Agammaglobulinemia

(X-linked recessive): - BTK signaling is required for progression beyond the pre-B-cell stage. BTK deficiency causes absent/reduced mature B cells and all immunoglobulin classes.

- Leads to inability to produce mature B-cells and Ig .

B-cell activation: T-cell dependent pathway: requires

previously activated CD4+ T cell

B-cell activation: T-cell dependent pathway: what are the steps

Peptide antigen binds to B-cell receptor. Presentation of antigen on MHC class II for T-cell receptor. Costimulation by CD40/CD40L needed. CD4+ T-cell activates B cell through different cytokines. Activated B cell produces IgM, undergoes class switching & affinity maturation.

B-cell activation: T-cell dependent pathway: activated B cell can become

plasma cell or memory B cell

B-cell activation: T-cell dependent pathway: B cell —> plasma cell —>

immunoglobulin production

B-cell activation: T-cell dependent pathway: what type of B cells important here

memory B cells

B-cell activation: T-cell dependent pathway: class switching

IgG, IgE, IgA

After B-cell is activated, it proliferates in the

germinal center of lymphoid tissue.

In the germinal center, what happens with B cells

mutations are created in variable part of binding region of activated B-cells.

outcome of affinity maturation

only the B cells with the highest affinity for pathogens will proliferate at a higher rate.

“Mutations occur throughout exon, but those ______ affinity to antigen are selected , a process called affinity maturation.”

improving

B-cell activation: T-cell Independent pathway: immediate response to

non-protein antigens (like bacterial liposaccharides)

B-cell activation: T-cell Independent pathway: what antibodies produced

only IgM

B-cell activation: T-cell Independent pathway: no class switching because

no CD40-CD40L interaction

B-cell activation: T-cell Independent pathway: activates what B cells

short lived plasma cells and no B cell memory

B-cell activation: T-cell Independent pathway: immunogenic?

weakly

Conjugated Vaccines: explain the principle

Non-protein antigens → no T cell stimulation (T-cell independent pathway) → weaker immune response & weaker protection. So… The B cell binds the polysaccharide, internalizes the conjugate, and presents a carrier protein peptide on MHC II to a helper T-cell. CD40/CD40L signaling then permits class switching and memory against the polysaccharide.

Conjugate a polysaccharide antigen to peptide antigen → B cell generates antibodies to polysaccharide + protein antigen presented to T cells + T cells can improve the B cell response → strong immune response & protection.

Using T-dependent pathway + immunity to polysaccharide antigen.

examples of conjugated vaccines

E.g., H. influenza type B vaccine, Neisseria meningitidis, Strep. pneumoniae.

B-1 cells

make immunoglobulins, T independent (respond to IgM)

marginal zone B cells

T independent (respond to IgM)

follicular B cells

very diverse VDJ repertoire on heavy and light variable regions. T-dependent (depend on T-cells for help; make IgE, IgG, IgA). Mainly IgG.

B10 cells

produce IL-10

B cell Anergy

when B-cell cannot become activated due to lack of co-stimulatory signal. A form of Self-Tolerance.

IMPORTANT: B-Cell markers:

CD 19, CD 20, CD 21, CD 40, MHC CLASS II, B7.

Enzyme Activation Induced Cytidine Deaminase (AID) in B-cells is responsible for

class switching & somatic hypermutation. This helps make antibodies better.

1. What does a BCR recognize compared with a TCR?

1. A BCR recognizes native intact antigen. A TCR recognizes processed peptide presented on MHC.

2. Which MHC class presents endogenous antigen, and to which T cell?

2. MHC I presents endogenous antigen to CD8 T cells.

3. An NK cell kills an IgG-coated target. Which receptor is responsible?

3. CD16, also called Fc gamma RIII, mediates ADCC.

4. Which chains use VDJ rather than VJ?

4. Immunoglobulin heavy chains and TCR beta chains use VDJ.

5. What is the difference between RAG and AID?

5. RAG creates the initial receptor through V(D)J recombination. AID later performs somatic hypermutation and class switching.

6. A boy has absent B cells and low levels of every immunoglobulin class. What is the defect?

6. BTK deficiency causing X-linked agammaglobulinemia.

7. A patient has high IgM with low IgG, IgA, and IgE. What classic defect should you suspect?

7. CD40 ligand deficiency causing X-linked hyper-IgM syndrome.

8. Why does conjugating a polysaccharide to a protein improve vaccination?

8. The B cell presents carrier-protein peptide to helper T cells, gaining CD40-CD40L signaling, class switching, affinity maturation, and memory.

T cell development and selection location of progenitor cells

Progenitor cells from bone marrow travel to the thymus T cell differentiation/positive selection occurs in the cortex of Thymus

T cells: positive selection

T cells with WEAK responses to MHC are selected for (Kept)

- CD4+ and CD8+ cells present

- CD8+ cells will bind class I MHC

- CD4+ cells will bind class II MHC

T cells: negative selection

T cells with strong responses to self (reactive) are eliminated

- Self-antigen presentation with autoimmune regulatory protein (AIRE)

T cells: negative selection occurs in the

medulla

T cells: negative selection: what are separated?

CD4+ and CD8+

Regulatory T cells: function

maintain specific immune tolerance by suppressing CD4+ and CD8+ T-cell effector functions

Regulatory T cells: express

CD3, CD4, CD25, and FOXP3 on surface

Regulatory T cells: when activated

they produce anti-inflammatory cytokines

- IL-10 and TGF-B (immune suppressive)

- Promote wound healing

Regulatory T cells: immunologic tolerance

- Immunologic unresponsiveness

- Only receptor bearing cells have tolerance, (Tregulatory)

- Causes apoptosis and anergy

TH1 cells: signature cytokines, immune reactions, host defense, role in diseases

TH2 cells: signature cytokines, immune reactions, host defense, role in diseases

TH17 cells: signature cytokines, immune reactions, host defense, role in diseases

Tfh cells: signature cytokines, immune reactions, host defense, role in diseases

During a study on the immune system, an investigator isolates and labels T cells from the cortex of the thymus. The T cells that do not bind cortical epithelial cells expressing MHC molecules undergo apoptosis within 3-4 days. Which of the following best describes the T cells during this phase of differentiation?

CD4+ and CD8+

MHC have ____ in each cleft, allowing specific different types of peptides to be presented

anchor residues

MHC restriction

- Only recognize peptides which they were educated

B2 Microglobulin associated with

MHC class I

MHC Class I genes:

HLA-A,B,C,E,F,G

MHC class I located on

all cells except RBCs

MHC Class II genes:

HLA-DR,DQ,DP

A 67-year-old man comes to the physician because of a 3-day history of fever, chills, headache, and fatigue. He appears ill. His temperature is 39°C (102.2°F). Analysis of nasal secretions shows infection with an enveloped, single-stranded segmented RNA virus. In response to infection with this pathogen, certain cells present antigens from the pathogen to CD8+ T-lymphocytes. Which of the following statements about the molecules used for the presentation of these antigens is most accurate?

MHC Class I presentation

MHC Class II presentation

Difference between MHC class I and MHC class II

Naive T cell Activation: anchor with

LFA-1 (on T cell)

ICAM-1 (on APC)

Naive T cell Activation: costimulatory signal

B7 (on APC) binds to CD28 (on T cell)

CD40 on ___ binds to CD40L on ____

APC, T cell

CD40 on APC binds to CD40L on T cell →

B7 expression - amplification

APCs with MHC I activate TCRs on CD8+ cells which induces

Induce apoptosis for intracellular (infecting the APC) pathogens -

1. Activation of granzymes that contain perforin B -

2. Activation of Fas-FasL pathway signaling internal apoptosis pathway

A 32-year-old man with HIV comes to the physician because of a 2-month history of weight loss, night sweats, and productive cough. Auscultation of the lungs shows coarse crackles at the right upper posterior field. An x-ray of the chest shows an opacity in the right upper lobe. Sputum analysis shows acid-fast bacilli. A small amount of tuberculin fluid is injected into the subcutaneous tissue on the left forearm. Examination of the injected area 48 hours later shows no induration or erythema. Impairment of which of the following processes is the most likely cause of the negative tuberculin skin test seen in this patient?

innate vs adaptive immune response

innate immune system recognition

PAMPs and DAMPs (Cell lipids, LPS and dsRNA)

TLRs, NOD-like receptors, complement recognize PAMPs and DAMPs and release NF-kB, release type I interferon, complement activation, inflammasome, activating innate immune system

Type I interferon then can activate adaptive immune system (antiviral state)

humoral immunity

B Cell activation : Production of Ig’s protecting against extracellular pathogens

cellular immunity

T cell activation

i. Defense against mainly intracellular pathogens

ii. Bind peptide fragments from MHCs

adaptive immunity

T cells recognize antigen in peripheral tissues → CD4+ promotes cytokine release and phagocytosis, CD8+ is cytotoxic

what is class switching

dependent activation of B cells

Complement coated pathogen (C3d) binds to BCR2 and CD21 → Dependent activation of B cells

_____ needed for isotype switching

CD40/CD40Lhy

Hyper IgM labs

high IgM, low IgA/G/E

Hyper IgM common infections

Pneumocystis jirovecii infections

Hyper IgM treatment

stem cell transplant

3 main types of Hyper IgM

A 24-year-old woman comes to the physician for progressively worsening episodes of severe crampy abdominal pain and nonbloody diarrhea for the past 3 years. Examination of the abdomen shows mild distension and generalized tenderness. There is a fistula draining stool in the perianal region. Immunohistochemistry shows dysfunction of the cytosolic nucleotide oligomerization binding domain 2 (NOD2) receptor. In-vitro studies show that this receptor is usually involved in activation of the innate immune system in response to certain pathogen-associated patterns (PAMPs). Which of the following proteins is most likely to be produced upon activation of this receptor?

immunodeficiency definition

Absence/malfunction of immune system

causes of immunodeficiency

Primary- Genetic cause External Factor - transplant, HIV, chemo