False-colour transmission electron micrograph (TEM) of a human white blood cell (bottom), showing presence of an HLA antigen (human leucocyte antigen), which appears as uneven red areas on exterior suface of the cell. The HLA antigens arise from a gene cluster on chromosome 6 in humans, which is referred to as the Major Histocompatability Complex (MHC). This title arose through studies on graft rejection in mice, where matched groups of antigens in donor & recipient animals markedly improved graft survival. In addition, it is now recognized that HLA antigens are involved in many other immunological processes. Magnification: X 8,800 at 35mm size.