Comparison Between Murine Natural Antibodies and Natural Killer Cells: Recognition of Separate Target Structures As Revealed by Differential in Vitro Expression and Dependence on Glycosylation

The specificity of complement-fixing, cytotoxic antibodies against the YAC lymphoma in sera of normal young adult (A X C57BL)F1 mice was studied. In vivo-maintained, immunoselected sublines of the YAC lymphoma expressed low amounts of the natural antibody (NAb) target structure. These cell lines were also resistant to natural killer (NK) cell-mediated lysis. After 2-3 weeks of in vitro culture the immunoselected cell lines became NK sensitive, but they remained resistant to NAb. When several independently derived variants selected for low NK sensitivity were tested for their ability to absorb NAb, the degree of absorption varied considerably among the variants. NAb could be inhibited by purified C-type virus particles and also by bacterial sonicates and various glycoprotein preparations. Treatment of target cells with tunicamycin, an inhibitor of asparagine-linked glycosylation, decreased the sensitivity to NAb lysis but had no impact on NK sensitivity. Thus the results indicated that a) NAb and NK cells recognized separate target structures and b) the target structure(s) for NAb but not for NK cells were saccharides of the N-glycosidic type.