MD-1 has an important role in cell surface expression of human RP105. Two IL-3–dependent lines, BaHRP (A through D) and BaHRPMD (E through G), were stained with either the anti-RP105 MoAb MHR73 (the left column) or the anti-flag MoAb M2 (the right column). Cell permeabilization was conducted in (C), (D), and (G). RP105 and MD-1 were tagged with the flag epitope at carboxy-terminus. Carboxy-temini of RP105 and MD-1 are located inside or outside cells, respectively. Therefore, the anti-flag MoAb detects MD-1 but not RP105 in cell surface staining of BaHRPMD cells (F).