Antigen Processing and Presentation

Questions and Answers

What is the primary role of MHC molecules in the immune response?

To mediate direct pathogen destruction

To produce antibodies in response to an infection

To transport glucose across cell membranes

To present antigen peptides to T cells (correct)

Which type of antigen presenting cells do MHC class II molecules primarily utilize?

Professional antigen presenting cells (correct)

Only tumor cells

All types of body cells

Neutrophils exclusively

Which statement correctly describes MHC class I molecules?

They are only found on B cells.

They present to helper T cells exclusively.

They are larger than MHC class II molecules.

They present antigens from intracellular sources. (correct)

What happens to an antigen after it is engulfed by a cell for processing?

It is degraded into peptide fragments for MHC association. Signup and view all the answers

How are T cells activated by the antigen-MHC complex?

Through binding to the MHC-antigen complex via TCR Signup and view all the answers

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

To bind processed antigen peptides for T lymphocyte recognition Signup and view all the answers

Which class of MHC molecules is primarily expressed on professional antigen presenting cells?

MHC Class II Signup and view all the answers

Which of the following correctly describes MHC Class I molecules?

Present peptides derived from endogenous proteins Signup and view all the answers

What are the components of MHC Class II molecules?

α1, α2, β1 and β2 Signup and view all the answers

Which statement is true regarding the human leukocyte antigen (HLA)?

HLA molecules exhibit polymorphism with many alleles 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 essential concepts of antigen processing and presentation, focusing on the structure and function of MHC class I and II proteins. Participants will explore the roles these molecules play in the immune response and identify various antigen presenting cells. It also delves into the interactions between T helper cells and the immune system.