<P> Diversity of antigen presentation, mediated by MHC classes I and II, is attained in at least three ways: (1) an organism's MHC repertoire is polygenic (via multiple, interacting genes); (2) MHC expression is codominant (from both sets of inherited alleles); (3) MHC gene variants are highly polymorphic (diversely varying from organism to organism within a species). Major histocompatibility complex and sexual selection has been observed in male mice making mate choices of females with different MHCs and thus demonstrating sexual selection . Also, at least for MHC I presentation, there has been evidence of antigenic peptide splicing which can combine peptides from different proteins, vastly increasing antigen diversity . </P> <P> The first descriptions of the MHC were made by British immunologist Peter Gorer in 1936 . MHC genes were first identified in inbred mice strains . Clarence Little transplanted tumors across differing strains and found rejection of transplanted tumors according to strains of host versus donor . George Snell selectively bred two mouse strains, attained a new strain nearly identical to one of the progenitor strains, but differing crucially in histocompatibility--that is, tissue compatibility upon transplantation--and thereupon identified an MHC locus . For this work, Snell was awarded the 1980 Nobel Prize in Physiology or Medicine, together with Baruj Benacerraf and Jean Dausset . </P> <P> Of the three MHC classes identified, attention commonly focuses on classes I and II . By interacting with CD4 molecules on surfaces of helper T cells, MHC class II mediates establishment of specific immunity (also called acquired immunity or adaptive immunity). By interacting with CD8 molecules on surfaces of cytotoxic T cells, MHC class I mediates destruction of infected or malignant host cells, the aspect of specific immunity termed cellular immunity . (The other arm of specific immunity is humoral immunity, whose relation to MHC is more indirect .) </P> <P> MHC is the tissue - antigen that allows the immune system (more specifically T cells) to bind to, recognize, and tolerate itself (autorecognition). MHC is also the chaperone for intracellular peptides that are complexed with MHCs and presented to T cell receptors (TCRs) as potential foreign antigens . MHC interacts with TCR and its co-receptors to optimize binding conditions for the TCR - antigen interaction, in terms of antigen binding affinity and specificity, and signal transduction effectiveness . </P>

Which of the following recognizes antigens displayed on host cells with mhcii