Use of monoclonal antibodies to a human cytotoxin for its isolation and for examining the self-induction of resistance to this protein.

Crude preparations of cytotoxins (CTXs) produced by human peripheral blood mononuclear cells exert a marked cytotoxic effect when applied to cells in the presence of cycloheximide but in its absence can induce resistance to cytotoxicity. To examine the relationship between these cytotoxic and protective activities, we attempted to fully dissociate the CTX from the other proteins secreted by mononuclear cells. Mice injected with preparations of the cytokines secreted by peripheral blood mononuclear cells developed significant titers of serum antibodies to CTX(s). Splenocytes of such immunized mice were fused with NSO myeloma cells; a few among the resulting hybridoma cells secreted CTX-binding antibodies. Immunoadsorbents constructed with a monoclonal antibody produced by one of these hybridomas were used to purify to homogeneity a CTX (Mr approximately 17,500) from crude preparations of cytokines, by a single adsorption and elution cycle. Purified CTX was cytotoxic in the presence of cycloheximide but in its absence induced resistance to cytotoxicity; this resistance was manifested by decreased vulnerability to CTX in a subsequent incubation in the presence of cycloheximide. We conclude that CTX itself can induce certain changes in cells, which are reflected in resistance to its own cytotoxic effect.