1-5 Major Histocompatability Molecules and the Detection of Infection

Question 1

Cluster of Differentiation (CD)

Answer 1

The basis of a system for identifying cell surface molecules of immune cells by the use of antibodies and in which each molecule is given a specific number prefixed by CD to form the basis of a systematic nomenclature. The term cluster reflects the fact that each molecule is usually recognized by a group, or cluster of antibodies; and the appearance of the molecules usually reflects different differentiated states of the cell, hence differentiation. Surface marker molecules of immune cells of different types and at different stages of differentiation or activation have been identified in this way and can be used to classify cells, or to follow their progress through development or their activation status.

Question 2

Coreceptor

Answer 2

Receptor on a T cell that recognizes invariant parts of MHC molecules and forms a recognition complex with the antigen receptor and contributes to intracellular signaling. The coreceptor CD8 binds to MHC class I molecules and is generally expressed on cytotoxic cells; the coreceptor CD4 binds to MHC class II molecules and is generally found on helper cells.

Question 3

Major Histocompatibility Complex (MHC)

Answer 3

Cluster of genes encoding the classical and many non-classical MHC molecules and other structurally unrelated molecules, many with important functions in immunity.

Question 4

Major Histocompatibility Complex (MHC) molecules

Answer 4

Cell surface glycoproteins encoded in the major histocompatibility complex and which bind degraded fragments derived from intracellular proteins and display them on the cell surface.

Question 5

MHC Class I molecules

Answer 5

Are expressed on virtually all body cells and bind peptides generated by cytoplasmic proteases from cytoplasmic proteins. Protein displayed on MHC class I molecules is recognized by cytotoxic T cells, which kill infected cells.

Question 6

MHC class II molecules

Answer 6

Normally expressed only on cells of the immune system and bind peptides generated from internalized antigen in the endosomal compartments of cells. Antigen displayed by MHC class II molecules is recognized by naïve T helper cells at the initiation of immune responses.