These proteins are found on the surface of cells and play a crucial role in the immune system's ability to recognize and respond to foreign invaders, such as viruses, bacteria, and parasites.

There are two main classes of MHC proteins:

* MHC Class I: These proteins are found on all nucleated cells in the body. They present fragments of proteins from inside the cell to CD8+ T cells, which are cytotoxic T cells that can kill infected or cancerous cells.

* MHC Class II: These proteins are found on antigen-presenting cells (APCs), such as macrophages, dendritic cells, and B cells. They present fragments of proteins that have been engulfed by the APC to CD4+ T cells, which are helper T cells that can activate other immune cells.

In summary: MHC genes code for MHC proteins, which are crucial for the immune system's ability to recognize and respond to foreign invaders. There are two main classes of MHC proteins, each with a distinct role in immune function.