Antigen Processing and Presentation

Questions and Answers

What function does the Major Histocompatibility Complex (MHC) serve in the immune response?

It produces antibodies for B cells to recognize antigens.

It functions only in the regulation of B cell activation.

It presents antigen fragments to T cells for recognition. (correct)

It directly kills pathogens and infected cells.

Which class of MHC is primarily involved in presenting antigens to CD8+ T cells?

MHC class II

MHC class IV

MHC class I (correct)

MHC class III

What is a unique characteristic of MHC class II molecules?

They are present on all nucleated cells.

They are found only in professional antigen presenting cells. (correct)

They can present non-peptide antigens.

They primarily activate cytotoxic T cells.

What happens to an antigen after it is captured by a cell?

It is degraded into protein peptides and associates with MHC molecules. Signup and view all the answers

How do T cells primarily recognize antigens?

By recognizing antigens as peptides presented by MHC molecules. Signup and view all the answers

What is the primary function of Major Histocompatibility Complex (MHC)?

To bind to processed antigen peptides for recognition by T lymphocytes. Signup and view all the answers

Which of the following cells primarily express MHC Class II molecules?

Macrophages. Signup and view all the answers

What type of peptides do MHC Class I molecules present?

Peptides derived from endogenous proteins. Signup and view all the answers

Which of the following correctly describes MHC Class II molecule structure?

Consists of four domains, α1, α2, β1, and β2. Signup and view all the answers

What distinguishes HLA class I from HLA class II in humans?

HLA class I is expressed on all nucleated cells. Signup and view all the answers

Study Notes

Antigen Processing and Presentation

Antigen processing involves capturing and degrading antigens for presentation to T cells via Major Histocompatibility Complex (MHC) molecules.
T cells require peptide-MHC complexes for recognition, while B cells can bind free antigens directly.
MHC molecules, encoded by multiple loci, present processed antigen fragments to T cells, pivotal for initiating an immune response.
MHC class I (HLA class I) is present on all nucleated cells, presenting endogenous peptides to CD8+ T cells.
MHC class II (HLA class II) is mainly found on professional Antigen Presenting Cells (APCs) like dendritic cells, macrophages, and B cells, presenting exogenous peptides to CD4+ T cells.

Structure and Function of MHC

MHC class I consists of four domains (α1, α2, α3, and β2-microglobulin) and interacts with CD8+ T cells.
MHC class II consists of four domains (α1, α2, β1, and β2) and is recognized by CD4+ T cells.
Human MHC is referred to as Human Leukocyte Antigen (HLA) with two classes: HLA class I and HLA class II, each being polygenic and polymorphic.

Antigen Sources and Presentation Mechanisms

Endogenous antigens (e.g., viruses, tumors) are modified and presented via MHC class I; they undergo degradation in the cytosol by proteasomes.
Exogenous antigens (e.g., bacteria) are taken up through endocytosis or phagocytosis, processed in lysosomes, and presented via MHC class II.
For MHC class I loading, peptides are transported to the endoplasmic reticulum (ER) and bind to MHC class I molecules before transport to the cell surface.
MHC class II molecules are synthesized in the ER with an invariant chain blocking the peptide groove, replaced by antigen peptides after the chain is cleaved.

MHC Restriction and Immune Response

T cell recognition is dependent on peptide-MHC complexes; T cell receptors (TCRs) recognize these complexes rather than solitary peptides.
MHC restriction ensures T cells only respond to self-MHC-displayed peptides, crucial for distinguishing self from non-self.

Clinical Relevance

MHC compatibility is crucial in organ transplantation; mismatches can lead to rejection.
Certain MHC genotypes increase the risk of autoimmune diseases such as Type 1 diabetes and rheumatoid arthritis.
MHC diversity impacts susceptibility to infections and can affect disease outcomes in infections like HIV and malaria.
Understanding MHC's role in presenting tumor antigens can improve effectiveness in cancer immunotherapy and personalized medicine approaches.

Description

This quiz covers the critical concepts of antigen processing and presentation, focusing on MHC class I and II structures and functions. It explores their roles in the immune response, types of antigens processed, and the involvement of T helper cells. Ideal for students studying immunology.