Final answer:
The major histocompatibility molecule in humans is known as the human leukocyte antigen (HLA), which is crucial for the immune system to recognize self cells and in antigen presentation.
Step-by-step explanation:
In humans, the major histocompatibility (MHC) molecule is known as the human leukocyte antigen (HLA). These molecules are a set of glycoproteins expressed on the surface of all nucleated cells and play a critical role in the immune system.
The MHC molecules help the immune system to recognize the body's own cells as 'self' and are also crucial in antigen presentation, a process of significant importance in the activation of T cells. In organ transplantation, understanding HLAs is vital since they must be matched between donor and recipient to lower the risk of organ rejection.