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

Human embryonic myoblasts isolated from 13- to 19-week embryos were treated for 24 to 144 hr with 0.1-500 U/ml IFN-gamma and the constitutive and IFN-gamma-inducible MHC expression was examined by flow cytometry. Low levels of constitutive MHC I were expressed that increased with both developmental age and incubation time. In contrast, no constitutive MHC II was detected on human embryonic myoblasts at any age or incubation time. Both classes of MHC can be induced by IFN-gamma. Maximal MHC I induction increased in parallel with age, i.e., maximal induction occurred on 19-week myoblasts, while MHC II induction peaked at 17 weeks. IFN-gamma-induced expression of MHC I and II also increased with 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 findings for myoblast transfer therapy is discussed.