Antigen Processing and Presentation

Questions and Answers

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

To present antigen fragments to T cells. (correct)

To produce antibodies to neutralize pathogens.

To engulf and digest pathogens directly.

To initiate inflammation in tissues.

Which of the following accurately describes the difference between MHC class I and class II molecules?

MHC class I is found on all nucleated cells, while class II is only found on professional antigen-presenting cells. (correct)

MHC class II has a single binding groove, while class I has two.

MHC class I molecules can only present non-peptide antigens.

MHC class I presents to CD4+ T cells, while class II presents to CD8+ T cells.

What role do T helper cells play in immunity?

They produce antibodies independently of B cells.

They regulate both cell-mediated and humoral immune responses. (correct)

They only assist in the recognition of antigens.

They directly kill infected cells.

How are antigens processed and presented by class I MHC molecules?

Cytosolic proteins are degraded and presented as peptides on MHC class I. Signup and view all the answers

What is meant by cross-presentation in the context of antigen presentation?

The presentation of extracellular antigens by cells expressing MHC class I. Signup and view all the answers

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

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

Which of the following statements about MHC Class II molecules is correct?

They are mainly found on professional antigen presenting cells. Signup and view all the answers

What distinguishes MHC Class I molecules from MHC Class II molecules?

MHC Class I is expressed on all nucleated cells, whereas MHC Class II is limited to professional APCs. Signup and view all the answers

Which of the following is NOT a characteristic of Human Leukocyte Antigen (HLA) Class I molecules?

They present peptides derived primarily from exogenous sources. Signup and view all the answers

Which antigen presenting cells primarily express MHC Class II molecules?

Dendritic cells, macrophages, and B 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 essential concepts related to the structure and function of MHC class I and II proteins. You will learn about their role in the immune response, types of antigens processed, and the importance of antigen presenting cells. Test your understanding of T helper cell roles in immune reactions.