CHAPTER 3 Antigen Capture and Presentation to Lymphocytes

Vocabulary flashcards covering antigen receptor recognition, the structure and function of MHC class I and II, and the intracellular processing pathways for protein antigens based on the course MEDL 234.

T-cell receptor (TCR)

The antigen receptor for most T cells that recognizes only protein antigens, specifically peptides displayed on MHC molecules.

B-cell receptor (BCR)

A membrane-bound immunoglobulin that recognizes a variety of macromolecules (proteins, polysaccharides, lipids, nucleic acids) in soluble or cell-associated form, as well as small chemicals.

Major histocompatibility complex (MHC)

Membrane proteins involved in the presentation of peptide antigens for recognition by T cells; known in humans as human leukocyte antigens (HLA).

MHC Restriction

The property where CD4+ and CD8+ T cells only recognize peptides when they are displayed by MHC molecules.

Professional Antigen Presenting Cells (APCs)

Cells including dendritic cells, macrophages, and B cells that express MHC class II molecules and present foreign antigens to CD4+ T cells.

Target Cells

Nucleated cells that express MHC class I and can present cytosolic antigens to CD8+ cytotoxic T lymphocytes.

Dendritic Cells (DCs)

The principal inducers of T-dependent responses primarily involved in capturing antigens and activating naïve T cells for expansion and differentiation.

Haplotype

A group of MHC genes inherited together as a set from one parent.

Co-dominant expression

A property of MHC genes where both inherited paternal and maternal alleles are expressed, maximizing the variety of peptides an individual can display.

Anchor residues

Amino acid side chains of a peptide that insert into pockets in the floor of the MHC molecule's peptide-binding cleft to attach the peptide.

Polymorphism

The existence of many different alleles (variants) for a gene within a population, which for MHC ensures some members can present any particular microbial protein.

Ubiquitin

A peptide used to tag cytosolic or nuclear proteins for degradation in the MHC class I pathway.

Proteasome

A catalytic complex of proteolytic enzymes that degrades ubiquitinated proteins into peptide fragments in the cytosol.

Transporters Associated with Antigen Processing (TAP)

An ATP-dependent heterodimer (TAP-1 and TAP-2) that transports peptides from the cytosol into the lumen of the endoplasmic reticulum (ER).

Tapasin

A membrane-anchored TAP-associated protein that brings the partially folded MHC class I alpha-chain:$\beta_2$ microglobulin complex into close proximity to TAP.

Invariant chain (Ii)

A protein chaperone that associates with MHC class II $\text{α}$ and $\text{β}$ chains in the ER, directing them to acidic endocytic vesicles.

Class II invariant chain peptide (CLIP)

A small part of the invariant chain that remains bound to the peptide-binding groove of MHC class II to prevent premature peptide binding.

HLA-DM

A non-classical MHC class II molecule that mediates the exchange of CLIP for an antigenic peptide in the MHC class II loading compartment.

Cross-presentation

A process where dendritic cells ingest extracellular antigens and present them on MHC class I molecules to activate or prime naïve CD8+ T cells.

Follicular dendritic cells (FDCs)

Non-bone-marrow derived cells in B cell follicles that display antigens coated with antibody or complement to select high-affinity B cells.

CCR7

A chemokine receptor expressed by activated dendritic cells and naïve T cells that promotes their entry into the T cell areas of lymph nodes.

DR public (DRp)

A term used to describe the gene product for the DRB3, DRB4, or DRB5 genes which can increase the number of expressed class II molecules.