Structural Aspects of CD4 and CD8 Involvement in the Cellular Immune Response

Thymus-derived lymphocytes (T cells) participate in the cellular immune response, and they do so when stimulated into action through interactions between T-cell receptor molecules on their surfaces and peptide antigens presented on target cell surfaces as complexes with molecules of the major histocompatibility complex (MHC). Mature T cells are of two major types, dis-tinguished by the exclusive occurrence of either the CD4 or CD8 glycoproteins on their surfaces. The pre-dominant CD4-bearing (CD4 § CD8) cells are the help-er T cells, whereas the predominant CDS-bearing (CD4 CD8 +) cells are the cytotoxic or killer T cells. The CD4 § helper T cells are restricted to interact with class II MHC molecules, which occur on certain im-mune system cells such as macrophages and B cells