IBS week 1 adaptive immunity

What are the two main cell types of the adaptive immune system

T cells and B cells.

Where do T cells mature

In the thymus.

Where do B cells mature

In the bone marrow.

What triggers the adaptive immune response

Recognition of specific antigens by B or T cell receptors.

What is the main advantage of adaptive immunity

It provides specificity and immunological memory.

What are antigens

Molecules that can be recognized by antibodies or T/B cell receptors.

What is an epitope

The specific part of an antigen recognized by a receptor or antibody.

What do B cell receptors (BCRs) recognize

Native antigens on the pathogen surface.

What do T cell receptors (TCRs) recognize

Peptide fragments presented by MHC molecules.

What are the two main types of T cells

CD4⁺ helper T cells and CD8⁺ cytotoxic T cells.

Which T cell recognizes MHC class I

CD8⁺ cytotoxic T cells.

Which T cell recognizes MHC class II

CD4⁺ helper T cells.

What does MHC class I present

Endogenous peptides from intracellular proteins.

What does MHC class II present

Exogenous peptides from phagocytosed material.

Where is MHC I expressed

On all nucleated cells.

Where is MHC II expressed

On professional antigen-presenting cells (APCs) like DCs, macrophages, and B cells.

What is MHC restriction

T cells only recognize antigens presented on self-MHC molecules.

What is the structure of MHC I

α-2 & 3 associated with α-1 & β₂-microglobulin.

What is the structure of MHC II

α-1 & 2 associated with β1 & β₂-microglobulin.

What is polymorphism in MHC

Many different allotypes exist in the population for each MHC isotype.

Why is MHC polymorphism important

It allows diverse peptide presentation and protection against many pathogens.

What are human MHC molecules called

Human Leukocyte Antigens (HLA).

What genes encode MHC I molecules

HLA-A, HLA-B, and HLA-C.

What genes encode MHC II molecules

HLA-DP, HLA-DQ, and HLA-DR.

Where are MHC genes located

On chromosome 6.

How do cytotoxic T cells recognize infected cells

They detect viral peptides presented on MHC I.

What enzyme complex processes peptides for MHC I

The proteasome.

How are MHC I peptides transported into the ER from the cytosol

By TAP (Transporter associated with Antigen Processing).

Where are MHC II peptides loaded

In the endosomal compartment after phagocytosis.

What blocks the peptide-binding groove of MHC II in the ER

The invariant chain (CLIP).

How is CLIP removed

By HLA-DM during MHC II peptide loading.

What is cross-presentation

DCs present exogenous antigens on MHC I to activate CD8⁺ T cells.

Why is cross-presentation important

It allows antiviral immunity even when DCs are not infected.

What is the function of CD4⁺ T cells

They help activate B cells, macrophages, and cytotoxic T cells via cytokines.

What is the function of CD8⁺ T cells

They kill virus-infected cells by releasing perforin and granzymes.

What is somatic recombination

Random rearrangement of V(D)J gene segments to generate receptor diversity.

Which enzyme catalyzes somatic recombination

RAG-1 and RAG-2 recombinase enzymes.

Where does T cell development occur

In the thymus.

What is the purpose of positive selection?

To ensure that developing T cells can recognize self-MHC molecules

What happens during negative selection

T cells that bind too strongly to self antigens are deleted.

What is central tolerance

Removal of Lymphocytes (T cells and B cells) that recognize the body’s own antigens during development.

Where does B cell negative selection occur

In the bone marrow.

What happens to B cells that bind self antigens in the bone marrow

They undergo receptor editing or apoptosis.

What are regulatory T cells (Tregs)

CD4⁺ cells that suppress inflammatory cells to prevent autoimmunity and maintain tolerance.

What causes autoimmune diseases

Failure of self-tolerance mechanisms.

What is clonal selection

Activation and expansion of a specific lymphocyte clone upon antigen recognition.

Where does T cell activation occur

In secondary lymphoid organs (lymph nodes, spleen).

What are the three signals required for T cell activation

1) Antigen recognition, 2) Costimulation, 3) Cytokine signals.

What provides costimulation to T cells

CD80/CD86 on APCs binding CD28 on T cells.

What happens if costimulation is absent

T cells become anergic or tolerant.

What do activated CD8⁺ T cells release

Perforin and granzymes to induce target cell apoptosis.

What cytokine drives T cell proliferation..

IL-2..

Which receptor binds IL-2

The IL-2 receptor (CD25 is its α-chain).

What are Th1 cells specialized for

Activating macrophages to kill intracellular pathogens.

What surface molecules mediate T–B interaction

CD40 on B cells and CD40L on T cells.

What is the outcome of CD40–CD40L interaction

B cell activation, Isotype (class) switching, Antibody affinity maturation, Germinal center and memory B cells formation,

What is the function of B cells

Produce antibodies and present antigen to T cells.

What happens after B cell activation

Differentiation into plasma cells and memory B cells.

What is a plasma cell

A differentiated B cell that secretes antibodies.

What is class switch recombination (CSR)

B cells change antibody isotype (IgM → IgG/IgA/IgE) while keeping specificity.

What enzyme mediates CSR and somatic hypermutation

AID (Activation-Induced Cytidine Deaminase).

What is somatic hypermutation

Introduction of mutations into V region genes to improve affinity.

Where does affinity maturation occur

In germinal centers.

What are germinal centers

Structures in lymph nodes where B cells undergo proliferation, mutation and selection.

What is isotype switching

Change of the constant region of antibody to alter function (e.g. IgM to IgG).

What is the first antibody produced in an immune response

IgM.

Which antibody predominates in the secondary response..

IgG..

Which antibody provides mucosal protection

IgA.

Which antibody is involved in allergy and parasite defense

IgE.

Which antibody functions mainly as a B cell receptor

IgD.

Which antibody crosses the placenta

IgG.

Which antibody forms a pentamer

IgM.

What are the main functions of antibodies

Neutralization, opsonization, and complement activation.

What is neutralization

Antibodies block pathogen attachment or toxin binding.

What is opsonization

Antibody-coated pathogens are phagocytosed via Fc receptors.

How do antibodies activate complement

Antibodies bound to antigen expose their Fc regions, allowing C1q to bind and activate the classical complement pathway, leading to cleavage of C3 and activation of downstream complement components

What is antibody-dependent cell-mediated cytotoxicity (ADCC)

NK cells, macrophages, neutrophils, or eosinophils recognize antibody-coated target cells via Fc receptors and induce apoptosis

What are memory cells

Long-lived B and T cells that respond rapidly upon re-exposure.

How do memory T cells differ from naïve T cells

They respond faster and require less costimulation.

Where do memory B cells reside

In lymphoid tissues and bone marrow.

What is a primary immune response

The first encounter with an antigen → slow and low-affinity IgM then IgG.

What is a secondary immune response

A faster, stronger response dominated by high-affinity IgG.

Why is immunological memory important

It provides long-term protection against re-infection.

What are cytokines

Small proteins that regulate the intensity and duration of immune responses.

Which cytokines promote inflammation

TNF-α, IL-1, IL-6.

Which cytokines are antiviral

Type I interferons (IFN-α, IFN-β).

Which cytokine is essential for B cell growth

IL-4.

Which cytokine is essential for T cell growth

IL-2.

Which cytokine activates macrophages..

IFN-γ..

Which cytokines inhibit inflammation

IL-10 and TGF-β.

What makes the adaptive immune response stop after infection?

When the antigen is gone, most immune cells die, and regulatory T cells turn off the remaining response.

What is immunological homeostasis

Balancing activation and suppression to prevent autoimmunity.

What is the ultimate goal of the adaptive immune response

To eliminate pathogens and create lasting protective memory.

Which cells express MHC class II molecules

Dendritic cells, macrophages, and B cells — the professional antigen-presenting cells (APCs) that activate CD4⁺ T helper cells.

Which cells receive help from T helper (CD4⁺) cells

B cells (for antibody production and class switching), macrophages (for enhanced microbial killing), and CD8⁺ cytotoxic T cells (for activation and memory formation).What are the five major CD4⁺ T helper subsets

What are the main cytokines produced by Th1 cells

IFN-γ.

What cytokines are produced by Th2 cells

IL-4, IL-5, IL-13.

What is the function of Th2 cells

Activate eosinophils and promote IgE-mediated responses against parasites.

What cytokines are produced by Th17 cells

IL-17 and IL-22.

What is the function of Th17 cells

Recruit neutrophils to fight extracellular bacteria and fungi.