Final answer:
Genes encode β2-microglobulin, a component of MHC class I involved in presenting endogenous antigens to T cells, and the invariant chain, which assists in the assembly and transport of MHC class II molecules for presenting exogenous antigens.
Step-by-step explanation:
The student asked about genes encoding the protein products β2-microglobulin and the invariant chain, and the roles of these proteins. The β2-microglobulin is a component of MHC class I molecules, which are essential for presenting endogenous antigens (originating from inside the cell) to T cells, triggering an immune response. It pairs with the longer alpha chain of MHC I, but only the alpha chain spans the cytoplasmic membrane, whereas β2-microglobulin stabilizes this complex on the cell surface.
The invariant chain, also known as CD74, plays a critical role in the proper assembly and transport of MHC class II molecules, which are responsible for presenting exogenous antigens (originating from outside the cell) to T cells. The invariant chain blocks the binding groove of MHC class II molecules while they are in the endoplasmic reticulum to prevent them from binding to peptides prematurely. Once MHC class II molecules reach the endosomal/lysosomal compartments, the invariant chain is degraded, allowing the binding groove to be available for antigen presentation.