Fibronectin and cellular cytotoxicity: Evidence against a role for fibronectin in natural killer activity

We investigated a possible role for fibronectin (Fn) in natural killer (NK) cell activity against K562 tumor cells. Plastic plates that had been incubated with Fn at 60 μg/ml bound 49.6% ± 12.8% (mean ± SEM) of K562 cells; plates coated with three other proteins bound essentially no tumor cells (P < 0.01). In similar experiments, 12.6% ± 4.7% of nonadherent lymphocytes bound to plates that had been coated with 60 μg/ml Fn; plates coated with other proteins bound ≤10% of these cells. Lymphocytes that bound to Fn-coated plates appeared to be slightly enriched for NK cells as assessed by morphology and by cytotoxic activity. Despite these findings, neither NK cytotoxic activity nor binding to K562 targets was affected by the addition of any of three anti-Fn antibody preparations, nor by the addition of exogenous Fn at concentrations found in plasma (300 μg/ml). Although Fn appears to bind both to K562 targets and to lymphocyte preparations that contain NK cells, it does not appear to have a functional role in mediating NK cell activity against K562 tumor cells.