Major Histocompatibility Complex

Question 1

MHC

Answer 1

The MHC genes encode heterodimeric membrane proteins that display peptides (foreign or self) on the cell surface for recognition by T cells. There are two structurally distinct types of MHC molecules. Class I MHC molecules (MHC I) are found on most nucleated cells and their function is to bind peptides derived from cytosolic proteins and present them to CD8+ T cells (Tc cells). Class II MHC molecules (MHC II) are found almost exclusively on professional APCs. MHC II molecules bind peptides derived from endocytosed proteins and present them to CD4+ T cells (Th cells).

Question 2

Helper T cell/lymphocyte (aka CD4+ T cell or Th cells)

Answer 2

A type of T cell, whose surface is marked by CD4 co-receptors, and who produces cytokines to help many different immune cell types. The helper T cell secretes cytokines that stimulate the activity of macrophages, B cells, Tc cells, and other immune cell types. Helper T cells recognize antigen presented in the context of MHC II molecules. Th cell cytokines can activate nitric oxide production by macrophages to kill phagocytosed microbes, promote B cell antibody production and isotype class switching in humoral immune responses, and help Tc cells proliferate.

Question 3

Cytotoxic T cell (aka CD8+ T cell or Tc cell or CTL)

Answer 3

A type of T cell bearing the CD8 co-receptor on its surface whose primary effector function is to recognize and kill host cells infected with viruses or other intracellular microbes. CTLs recognize microbial peptides displayed in the context of MHCI molecules. CTLs kill infected cells by releasing membrane pore-forming protein perforin, and apoptosis-inducing proteins granzymes. Perforin facilitates the entry of granzymes into the cell, and granzymes induce apoptosis of the infected host cell.

Question 4

Cytokines

Answer 4

A range of secreted proteins of low molecular weight produced by many different cell types that exert a stimulatory or inhibitory influence on the proliferation, differentiation, and function of cells of the immune system. Cytokines are principal facilitators of communication between cells of the immune system.

Question 5

MHC restriction

Answer 5

This term relates to Tc cells, and describes that the ability of antigen recognition by T cells is limited to antigen recognition in context of the MHC molecules. To elicit T cell activation, peptief antigens must be presented to a T cell by a MHC molecule.

Question 6

MHC I restriction

Answer 6

This term related to Tc cells. To elicit Tc cell activation, peptide antigens must be presented to a Tc cell by a MHCI molecule.

Question 7

MHCII restriction

Answer 7

This term relates to the Th cells. To elicit Th cell activation, peptide antigens must be presented to a Th cell by a MHCII molecule.

Question 8

Peptide binding groove/cleft

Answer 8

The portion of a MHC molecule that binds a peptide for display to appropriate T cell.

Question 9

Domain

Answer 9

A protein domain is a part of protein sequence and structure that can evolve, and function. Each domain forms a compact three-dimensional structure and often can be independently stable and folded. Proteins may consist of multiple domains, each ranging in size from 25 to 500 amino acids.