Proteins on the surface of T lymphocytes (q.v.) that determine their responses to antigens. Lymphocytes with the CD8 proteins on their surfaces function as killer T lymphocytes (Tk cells). Lymphocytes with the CD4 proteins on their surfaces function as helper T lymphocytes (Th cells). These secrete interleukins (q.v.), which activate Tk cells and B lymphocytes. See immunoglobulin domain superfamily.
Subjects: Genetics and Genomics.