MHC (Major Histocompatibility Complex) Class II antigens are polymorphic cell surface glycoproteins which bind foreign antigens and form a complex which is recognized by T lymphocyte antigen receptors. Presentation of foreign antigens by self MHC molecules to T cells triggers antigen-specific responses in the immune system. Thus, increasing the expression of MHC class II molecules on the surface of antigen-presenting cells contributes to the initiation and amplification of immune responses.