CD4 T-cell epitope mapping.

The majority of T cells recognize peptide epitopes bound to major histocompatibility complex (MHC)-encoded glycoproteins on the surface of professional antigen-presenting cells (APC), principally dendritic cells, macrophages, and B cells (1-3). Most T cells are specific for peptide epitopes in association with either classical MHC class Ia molecules (HLA-A, B, and C in humans and H2-K, D, and L in mice) in the case of CD8(+) T cells, or class II molecules (HLA-DR, DP, and DQ in humans and H2-A and E in mice) for CD4(+) T cells. However, a significant proportion of T cells recognize peptide antigens bound to nonclassical MHC class Ib molecules such as the human HLA-E (mouse analog Qa1) (4) and mouse H2-M3 (5). In addition, some T cells recognize not peptides but lipid or glycolipid antigens bound to nonclassical MHC class Ib molecules such as CD1 in both humans and mice (6).