Immunology: Antigen Capture and Presentation to Lymphocytes

This set of vocabulary flashcards covers the key proteins, cell types, and pathways involved in antigen capture and presentation within the immune system, specifically focusing on MHC classes and dendritic cell subsets.

Major Histocompatibility Complex (MHC)

A genetic locus whose principal protein products function as the peptide display molecules of the immune system.

MHC Restriction

The requirement that $CD4+$ and $CD8+$ T cells can see peptides only when they are displayed by that individual’s own MHC molecules.

Langerhans cells

The name given to epidermal dendritic cells located in the skin.

Plasmacytoid dendritic cells

Dendritic cells that morphologically resemble plasma cells, are present in the blood and tissues, and serve as the major source of type I interferons in innate immune responses to viral infections.

Classical dendritic cells

The majority subset of dendritic cells in tissues and lymphoid organs; they are characterized by high expression of $CD11c$ and are the most potent APCs for activating naive T lymphocytes.

$$CCR7$$

A chemokine receptor expressed by activated dendritic cells that is specific for chemoattracting cytokines produced by lymphatic endothelium and stromal cells in T cell zones of lymph nodes.

Class I MHC Molecules

Membrane proteins consisting of an \text{\alpha} chain associated with \text{\beta}_2\text{-microglobulin} that display peptides (typically $8$ to $9$ amino acids long) to $CD8+$ T cells.

Class II MHC Molecules

Membrane proteins consisting of two transmembrane chains (\text{\alpha} and \text{\beta}) that form a peptide-binding cleft accommodating peptides of $10$ to $30$ residues for display to $CD4+$ T cells.

Polymorphism

The property of MHC genes meaning that many different alleles (variants) are present among different individuals in the population.

Codominant expression

A property of MHC genes where the alleles inherited from both parents are expressed equally.

Anchor residues

Amino acids in a peptide antigen that fit into pockets in the floor of an MHC molecule's peptide-binding cleft to secure the peptide.

Proteasomes

Proteolytic complexes that degrade unfolded, ubiquitinated cytosolic proteins into peptides for the class I MHC pathway.

TAP (Transporter associated with antigen processing)

A molecule in the ER membrane that binds proteasome-generated peptides and actively pumps them into the interior of the ER.

Invariant chain ($I_i$)

A protein attached to newly synthesized class II MHC molecules in the ER that contains the CLIP sequence and targets the molecule to acidic endosomal/lysosomal vesicles.

CLIP (Class II invariant chain peptide)

A sequence within the invariant chain that occupies the peptide-binding cleft of a class II MHC molecule to prevent it from accepting peptides in the ER.

DM (HLA-DM)

A class II MHC–like protein that facilitates the exchange of CLIP in the class II MHC molecule for other peptides with higher affinity in acidic vesicles.

Cross-presentation

The process where a subset of classical dendritic cells ingests infected host cells or tumor antigens and displays them on class I MHC molecules to $CD8+$ T lymphocytes.

NK-T cells

Natural killer T cells that are specific for lipids displayed by class I–like $CD1$ molecules.

MAIT cells

Mucosal associated innate T cells specific for bacterial derived vitamin B metabolites displayed by class I–like $MR1$ molecules.

Costimulators

Molecules on APCs that serve as second signals for T cell activation, induced by microbial products via Toll-like receptors (TLRs).