Expression of Ia-like antigens on human erythroid progenitor cells as determined by monoclonal antibodies and heteroantiserum to Ia-like antigens

Abstract

Based on studies using anti-Ia-like heteroantisera, it has been concluded that human erythroid progenitor cells (CFU-E and BFU-E) express Ia-like antigens. We attempted to confirm these findings using a well-characterized anti-Ia-like heteroantiserum and hybridoma-derived monoclonal antibodies against Ia-like antigens. Specificity of the monoclonal antibodies was demonstrated by the pattern of reactivity against a panel of Ia-positive and Ia-negative cells and by immunochemical techniques. Normal human bone marrow or peripheral blood buffy coat cells were incubated with anti-Ia-like heteroantiserum or monoclonal antibody, with and without complement, washed, and plated with the appropriate humoral stimulator in semisolid media for determination of CFU-C, BFU-E, and CFU-E. Anti-Ia-like heteroantiserum produced complement-dependent inhibition of CFU-C-, BFU-E, and CFU-E-derived colony formation. Monoclonal anti-Ia-like antibody caused complement-dependent inhibition of CFU-C that persisted to a titer of 1:1000, but did not inhibit colony formation by BFU-E and CFU-E. Our results suggest either that erythroid progenitor cells do not express Ia-like antigens or that these antigens, if present, are expressed at very low density or in altered configuration, thus rendering them apparently unreactive with our monoclonal antibodies in a cytotoxicity assay.