HLA Genes and Molecules

In this chapter I describe the genomic organization of the MHC in humans, namely, the HLA system and the molecular structure of HLA class-I and class-II molecules. They are crucial in the interaction with T lymphocytes and NK cells determining their function. Other genes of the MHC complex are also described, including (a) the non-classical HLA-G, HLA-E and HLA-F, (b) genes coding complement components and (c) genes that play an important role in immunological functions involved in antigen presentation to T lymphocytes by regulating protein degradation into peptides (proteosomes) and their transport from the cytosol to the endoplasmic reticulum (peptide transporters, TAP). The HLA molecules are expressed in different tissues of our body with different intensity allowing T lymphocytes to monitor intracellular and extracellular infections. I have also included the description of the antigen processing and presentation machinery that presents processed antigens to T lymphocytes in a form of “small peptides” linked to a specific sequence within the structure of HLA molecules. This biological process is taking place in our cells allowing the formation of a complex of HLA class-I and class-II with an antigenic peptide.