ONTOGENY OF MAJOR HISTOCOMPATIBILITY COMPLEX ANTIGEN EXPRESSION ON CULTURED HUMAN EMBRYONIC SKELETAL

Human embryonic myoblasts isolated from 13- to 19-week embryos were tr eated for 24 to 144 hr with 0.1-500 U/ml IFN-gamma and the constitutiv e and IFN-gamma-inducible MHC expression was examined by flow cytometr y. Low levels of constitutive MHC I were expressed that increased with both developmental age and incubation time. In contrast, no constitut ive MHC II was detected on human embryonic myoblasts at any age or inc ubation time. Both classes of MHC can be induced by IFN-gamma. Maximal MHC I induction increased in parallel with age, i.e., maximal inducti on occurred on 19-week myoblasts, while MHC II induction peaked at 17 weeks. IFN-gamma-induced expression of MHC I and II also increased wit h incubation time. Induced expression of MHC I antigen reached plateau levels at 72 hr of IFN-gamma incubation, whereas MHC II increased to a plateau level at 120 hr. The immunological importance of these findi ngs for myoblast transfer therapy is discussed.