Final answer:
The HLAs that code for MHC class II molecules are HLA-DR, HLA-DQ, and HLA-DP. These genes are highly polymorphic, allowing for the diversity of the MHC-II molecules which are important for presenting antigens to CD4+ T-helper cells for an adaptive immune response.
Step-by-step explanation:
The human leukocyte antigen (HLA) system includes several genes that code for the major histocompatibility complex (MHC). Specifically for MHC-II, which is primarily expressed on antigen-presenting cells, the genes include HLA-DR, HLA-DQ, and HLA-DP. Each of these genes has many alleles, contributing to the diversity of the MHC-II molecules. MHC-II molecules have two subunits, an alpha (α) and a beta (β), which are approximately equal in size. These molecules are critical for the adaptive immune system because they present exogenously derived antigens (pathogens or environmental antigens that are internalized by the cell) to CD4+ T-helper cells, which can then mount a specific immune response.