Virus-specific HLA Class II-restricted Cytotoxic T Cells

Abstract

A hallmark of the immune response is that all T cell recognition functions are associated with components of the major histocompatability complex (MHC) [1,2]. Foreign antigens are recognized by T cells, only when these antigens are presented in association with self MHC molecules. The human MHC (HLA) is located on the short arm of chromosome six and encodes three general classes of molecules [3,4]. The HLA class I molecules, designated HLA-A, -B, and -C, consist of two subunits; a 44,000-dalton polymorphic heavy chain which is noncovalently associated with a nonpolymorphic 11,500-dalton light chain (β₂-microgloubulin). HLA class I molecules are expressed on the surface of virtually every cell type [3,4]. The HLA class II molecules, designated HLA-DR, -DP, and -DQ and collectively termed HLA-D, are composed of two noncovalently associated glycoproteins consisting of a 34,000-dalton heavy or α chain and a 29,000-dalton light or β chain. HLA class II molecules are present on a limited set of cell types, most notably B cells, macrophages, Langerhans cells, and activated T cells. The HLA class III molecules consist of several components of the complement system and are beyond the scope of this chapter.