Week 5 - Antigen Recognition by T Lymphocytes

These flashcards cover the key concepts of antigen recognition by T lymphocytes, focusing on T cell receptors, MHC classes, and their roles in the immune response.

What do T cell receptors (TCR) bind to in order to recognize foreign pathogens?

TCRs bind to pathogen proteins presented on other cells through major histocompatibility complex (MHC).

What are the two polypeptide chains in a T cell receptor?

TCRα and TCRβ.

What is the structure of the T cell receptor?

The TCR is a membrane-bound glycoprotein that has a variable (V) region and a constant (C) region.

How is T cell receptor diversity generated?

Diversity is generated through gene rearrangement in the thymus, similar to antibodies but without later hypermutation or isotype switching.

What happens when gene rearrangement of TCR does not operate correctly?

It results in severe combined immunodeficiency disease (SCID).

What is the role of the CD3 complex in T cell receptor function?

The CD3 complex assists with intracellular signaling alongside the TCR.

What distinguishes MHC class I from MHC class II?

MHC class I presents antigens from intracellular pathogens, while MHC class II presents antigens from extracellular pathogens.

What type of T cells recognize MHC class I molecules?

Cytotoxic (killer) T cells that express CD8 molecules.

What type of T cells recognize MHC class II molecules?

Helper T cells that express CD4 molecules.

What is the primary role of CD8 T cells?

To kill cells infected with intracellular pathogens.

How are peptides loaded into MHC class I molecules?

Peptides are transported into the endoplasmic reticulum (ER) and loaded by chaperones such as tapasin.

What is cross-presentation in the context of MHC?

It is the transfer of peptides from MHC class II to MHC class I, mostly not understood but involves antigen-presenting cells.

How does the MHC class II loading process occur?

After being made in the ER, MHC class II is blocked by the Invariant chain, which is then cleaved to allow peptides to bind with the help of HLA-DM.

What is notable about HLA polymorphism?

HLA loci exhibit a high degree of polymorphism, with thousands of allotypes across different MHC class I and class II molecules.

What role do proteasomes play in MHC class I processing?

Proteasomes degrade proteins into peptides, which are then loaded into MHC class I molecules.

What is the main function of MHC molecules?

To present peptide antigens to T cell receptors, initiating an immune response.