I'm going to try and explain what I think I know
From what I understand, MHC/HLA molecules present peptides to T cells. To be able to present peptides from a wide variety of pathogens, they need to have diversity in their peptide binding domains. My lecture handout tell me that MHC diversity comes due to polygeny and polymorphism. Polygeny refers to there being 3/6 (handout says 3, textbook says 6) MHC class I loci leading to 3/6 class I isotypes, and 3/5 MHC class II loci leading to 3/5 class II isotypes. Polymorphism refers to multiple alleles of each gene, meaning a variety of allotypes produced from each gene. These processes lead to the generation of a wide variety of isoforms of MHC proteins in the human population. The textbook also states that there is no rearrangement or structural change of the genes encoding the MHC proteins.
So I get that in the population, there is huge diversity of MHC molecules. But in each human, since there is no rearrangement of genes as in the case of antibodies to generate antibody diversity, is there therefore only one type of MHC protein being encoded? So by MHC diversity, we are not referring to diversity in each human, rather in the entire population? And if so, how do our MHC molecules become capable of binding to any antigen from any pathogen?
Please could someone clarify for me if I've misunderstood something, and also if my above explanation is factually correct, with the appropriate use of terminology?