NK-9, a distinct sialylated antigen of the T200 family

The nature and properties of antigens detected by a novel monoclonal antibody, NK-9, were studied. The NK-9 antigens had apparent molecular masses of 190, 200 and 220 kDa and were sensitive to neuraminidase and sodium metaperiodate treatments, which destroy the sialic acid residues of the cell surface glycoproteins. Trypsin treatment also removed the NK-9 reactivity, but the antigens were restored within a few hours thereafter. Tunicamycin, which inhibits the N-linked glycosylation after neuraminidase treatment, had no effect on the reappearance of the NK-9 positivity. Neither did endoglycosidase F, which removes the N-linked sugars, abolish the NK-9 antigenicity. Monensin, which blocks the cellular secretion, inhibited the restoration of the antigens, and monensin block also without preceding treatment with neuraminidase led to the disappearance of NK-9 reactivity, suggesting possible recycling molecules as carriers of the NK-9 detected epitopes. The NK-9 antigens appear to belong to the T200 antigen family, but are distinct from the antigens reactive with the available anti-T200 antibodies anti-LC, T29/33 and HLe-1, based on their different cell type distribution and absence of cross-reactivity in sequential immunoprecipitations.