and CHAPTER 6 Major Histocompatibility Complex (MHC) Molecules 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)

Features of Antigens Recognized by T Lymphocytes

PROPERTIES OF ANTIGENS RECOGNIZED BY T LYMPHOCYTES 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

T cell Recognition of a Peptide-MHC Complex

Functions of different antigen-presenting cells

Routes of Antigen Entry

Role of dendritic cells in antigen capture and presentation

THE MAJOR HISTOCOMPATIBILITY COMPLEX (MHC) Discovery of the Human MHC

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

MHC Genes

Map of the human MHC

Expression of MHC Molecules

MHC Molecules

PROCESSING OF PROTEIN ANTIGENS

The class I MHC pathway of antigen presentation

The class II MHC pathway of antigen presentation

Cross-presentation of antigens to CD8+ T cells

Presentation of extracellular and cytosolic antigens to different subsets of T cells

PRESENTATION OF NONPROTEIN ANTIGENS TO SUBSETS OF T CELLS 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