Myeloid‐associated antigen 3‐α‐fucosyl‐N‐acetyllactosamine (FAL): location on various granulocyte membrane glycoproteins and masking upon monocytic differentiation

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Abstract
Seven different granulocyte‐reactive murine monoclonal antibodies (mAb) were studied. The antigens recognized by these mAb were immunoprecipitated from lysates of 125I‐labeled granulocytes of healthy donors. The isolated antigens were analyzed by electrophoresis on sodium dodecyl sulfate‐polyacrylamide gel and autoradiography. All 7 antibodies precipitated the same 6 membrane polypeptides from membrane‐iodinated granulocyte lysates: 105 and 150‐kDa as most pronounced, together with 260‐, 230‐, 67‐ and 52‐kDa polypeptides. One of the antibodies studied, B4.3, is directed against 3‐α‐fucosyl‐N‐acetyllac‐tosamine as shown by absorption with the synthesized carbohydrate molecule. Competition experiments with 125I‐labeled B4.3 demonstrated complete inhibition of binding by B4.3 and 3 of the other antibodies (VIM D5, UJ308, MI/N1) and partial inhibition by the 3 other antibodies (FMC 10, FMC 12, FMC 13), indicating binding to the same antigenic structure. None of the 7 mAb reacted with monocytes in the immunofluorescence technique, but after neuraminidase treatment of these cells, positive reactions were obtained with all mAb. Immunoprecipitation with lysates of both native and neuraminidase‐treated monocytes showed no polypeptide bands. Monocytic differentiation of the cell line HL60 by 12‐0‐tetradecanoylphorbol‐13‐acetate (TPA) and of cell line U 937 by dimethylsulfoxide and TPA was accompanied by a decrease in reactivity with these antibodies, which could be recovered by neuraminidase treatment. This indicates that 3‐α‐fucosyl‐N‐acetyllactosamine is masked for the detection of the antibody upon monocytic differentiation by sialylation.
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