Final answer:
MHC molecules that are polygenic and polymorphic present a wide range of peptides to T cells. MHC I molecules are found on all nucleated cells, while MHC II molecules are exclusive to professional antigen-presenting cells. Matching MHC molecules is key to transplant success due to their polymorphic nature.
Step-by-step explanation:
MHC molecules present a broad range of peptides and are highly polymorphic, with multiple alleles at each locus contributing to their ability to bind various antigens. They display this broad specificity due to their polygenic and polymorphic nature, allowing for a wide array of peptide presentations. MHC class I molecules are found on all nucleated cells and present both self and nonself peptides to T cells. MHC class II molecules are expressed only on professional antigen-presenting cells, such as macrophages, dendritic cells, and B cells, and are involved in presenting nonself antigens for T cell activation.
A successful transplant often requires matching between donor and host MHC molecules, with a higher number of matches typically leading to a better outcome. This is due to the fact that humans have six MHC molecules that exhibit the most polymorphisms: three class I (A, B, and C) and three class II (DP, DQ, and DR). Matches are sought using a global registry due to the extensive polymorphism in MHC genes across individuals.