Major Histocompatibility Complexes and Antigen Presentation

MAJOR HISTOCOMPATIBILITY COMPLEXES AND ANTIGEN

PRESENTATION

As we’ve discussed briefly, there are major histocompatibility or MHC molecules on the surface of each cell in the body that allows immune cells to recognize the self. The MHC is found on all nucleated cells; in humans, they are called the human leukocyte antigens, made by HLA genes. Only mature RBCs do not express these because they have no nuclei.

There are two types of MHC molecules, called MHC I and MHC II. MHC I molecules are found on all cells, while MHC II molecules are found only on dendritic cells, macrophages, and B cells. These MHC II molecules will activate the T cells in the immune system. MHC molecules are glycoproteins that span the cell membrane. There are several subunits to these molecules and a cleft at the outer edge of these molecules that binds to antigens. Figure 55 shows the structure of these MHC molecules:

Figure 55.