Thymus-derived CD8+ TCRab+ T cells typically express heterodimericCD8ab consisting of a disulfide-linked a and b chain. CD8 can also be expressed as homodimeric CD8aa, namely on intra-epithelial T lymphocytes, some dendritic cells, NK, NKT and TCRcd+ T cells. Both forms of CD8 bind to the non-polymorphic domain of MHC classIa molecules and associate via CD8a with the intracellularSrc tyrosine kinase p56lck