Antigen Capture and Presentation to Lymphocytes

Practice flashcards covering the mechanisms of antigen capture, the structure and inheritance of MHC/HLA molecules, and the divergent pathways of Class I and Class II antigen processing.

T-cell receptor (TCR)

The antigen receptor for most T cells that can only see protein antigens when peptides derived from the protein are displayed on MHC molecules.

Major histocompatibility complex (MHC)

Membrane proteins involved in the presentation of peptide antigens for recognition by T cells, contained in class I and class II gene sets.

Professional antigen presenting cells (APCs)

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

Langerhans cell

Immature conventional dendritic cells (DCs) in the skin that form a network of cells with interdigitating processes.

Human leukocyte antigens (HLA)

The name for MHC gene products in humans, with genes located on chromosome 6.

Haplotype

A group of MHC genes inherited as a set, with one set inherited from each parent.

Co-dominant expression

A property of MHC molecules where both inherited alleles from the maternal and paternal haplotypes are expressed.

HLA-B

The most polymorphic HLA gene, with more than $10,500$ known alleles.

Anchor residues

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

Antigen processing

The physiological process of degrading a protein antigen into smaller peptide fragments.

Antigen presentation

The display of a peptide-MHC complex on the cell surface for recognition by T cells.

Ubiquitin

A peptide that tags proteins in the cytosol and nucleus for unfolding and degradation by the proteasome.

Proteasome

A catalytic complex composed of stacked rings of proteolytic enzymes that degrades unfolded proteins into peptides.

TAP (Transporters Associated with Antigen Processing)

A heterodimer (TAP-1 and TAP-2) that actively transports peptides from the cytosol into the ER lumen in an ATP-dependent manner.

Tapasin

A membrane-anchored protein that brings the partially folded MHC class I molecule into close proximity to TAP for efficient peptide loading.

Invariant chain (Ii)

A protein chaperone that associates with MHC class II chains in the ER and directs them to the acidic vesicles of the endocytic pathway.

CLIP (Class II invariant chain peptide)

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

MIIC (MHC class II compartment)

The specialized loading compartment formed by the fusion of endocytic vesicles and exocytic vesicles where peptide loading onto MHC class II occurs.

HLA-DM

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

Cross-presentation

A process by which some dendritic cells ingest extracellular antigens and present them on class I MHC molecules to CD8+ T lymphocytes.

Follicular dendritic cells (FDCs)

Non-bone-marrow derived cells in B cell follicles that display antigens to activated B cells using complement receptors (CR1, CR2) and antibody receptors.