The major histocompatibility complex (MHC) is a group of highly polymorphic molecules present on the surface of cells acting as antigen-presenting molecules (present the antigens to T cells to initiate an adaptive immune response).
In humans, MHC is known as human leukocyte antigen (HLA), and they are often used interchangeably.
There are three types of MHCs, but we will only cover the first two:
- MHC I -- Found on all of the cells of the body except for red blood cells. They consist of HLA A, B, or C molecules.
- MHC II -- Found only on professional antigen-presenting cells i.e B-cells, dendritic cells, and macrophages. They consist of HLA DP, DQ, or DR molecules.