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Major Histocompatibility Complex (MHC) Molecules
and
Antigen Presentation to T Lymphocytes
 Principal functions of T lymphocytes are defense against intracellular
microbes and activation of other cells, such as macrophages and B
lymphocytes
 All these functions require that T lymphocytes interact with other cells
 Task of displaying cell-associated antigens for recognition by T cells is
performed by specialized proteins that are encoded by genes in a locus
called the Major Histocompatibility Complex (MHC)
 Physiologic function of MHC molecules is the presentation of peptides to
T cells
 There are two main types of MHC gene products, called class I MHC
(present peptides to CD8+ CTLs) molecules and class II MHC (present to
CD4+ helper T cells) molecules
 The Mouse MHC (H-2 Complex)
 The genetic region that controlled graft rejection and contained several
linked genes was named the major histocompatibility complex (MHC)
 Human MHC or Human leukocyte antigens (HLA)
 Immune response (Ir) genes
 The best defined of these populations are NKT cells and γδ T cells
 NKT cells express markers that are characteristic of both natural killer (NK) cells and T
lymphocytes and express αβ T cell receptors with very limited diversity
 Class I–like “non-classical” MHC molecule called CD1
 γδ T cells recognize many different types of antigens, including some proteins and
lipids, as well as small phosphorylated molecules and alkyl amines