MHC Class I and Class II molecules are crucial components of the immune system, playing distinct roles in antigen presentation. They differ fundamentally in several aspects.
Both classes of MHC molecules are located on different chromosomes, which is a significant distinction. MHC Class I molecules are primarily encoded by genes on chromosome 6, while MHC Class II molecules are also encoded by genes on the same chromosome, though in a region that is closely linked yet distinct from Class I. Therefore, their location on the chromosome is not a point of distinction between them; they share proximity on chromosome 6.
The differences in their roles and functions highlight how they are expressed. MHC Class I molecules are expressed on nearly all nucleated cells, presenting endogenous antigens to CD8+ cytotoxic T cells. In contrast, MHC Class II molecules are mainly expressed on professional antigen-presenting cells like dendritic cells, macrophages, and B cells, stimulating CD4+ helper T cells.
Furthermore, the types of antigens they present also differ; MHC Class I primarily presents intracellular antigens, while MHC Class II presents extracellular antigens that have been engulfed and processed by the antigen-presenting cells.
In summary, the shared chromosomal location of M