A transmembrane protein complex composed of an MHC alpha chain and, in most cases, either an MHC class II beta chain or an invariant beta2-microglobin chain, and with or without a bound peptide, lipid, or polysaccharide antigen. [ GOC:add http://www.ncbi.nlm.nih.gov/pubmed/15928678 http://www.ncbi.nlm.nih.gov/pubmed/16153240 https://www.worldcat.org/search?q=bn%3A0781735149 GOC:jl ]