major histocompatibility molecule

major histocompatibility molecule

[¦mā·jər ‚his·tō·kəm‚pad·ə′bil·əd·ē ′mäl·ə‚kyül] (immunology) Any of two classes of immunoregulatory cell-surface glycoproteins that are encoded by the major histocompatibility gene; class I molecules are found on almost every nucleated body cell and present antigens from the cytoplasm to cytotoxic T cells, whereas class II molecules are found only on macrophages, B cells, and CD4+ T cells and present antigens from outside the cell to helper T cells.