MoAbs 103B2/9E10 and 105.A5 identify an antigen expressed by cultured HBMSCs. The expression of the antigen identified by MoAbs 103B2/9E10 and 105.A5 was assessed by indirect in situ immunofluorescence (as described in Materials and Methods). Cytoplasmic and membrane staining was detected for both 103B2/9E10 (B) and 105.A5 (D). IgG₃ (A) and IgM (C) nonbinding, control antibodies demonstrate no detectable levels of immunofluorescence.