Diphtheria toxin and related proteins: effect of route of injection on toxicity and the determination of cytotoxicity for various cultured cells.

The effect of route of injection on the toxicity of intact diphtheria toxin, cross-reacting material (CRM45), and diphtherial fragment A was compared in several animal species. By ordinary routes of injection, neither CRM45 nor fragment A was toxic, even in species for which 0.1 micrograms of toxin/kg of body weight was lethal. After intracerebral injection, however, small amounts of CRM45 led to paralysis and death, even in mice and rats--species that are resistant to toxin administered intravenously. High doses of fragment A were nontoxic even by the intracerebral route. The cytotoxic dose od CRM45 was approximately 10(-7) M for a variety of cell lines derived from toxin-sensitive or toxin-resistant species. Cultured at Schwann's cells, however, were more sensitive CRM45 than other cell lines tested and 50-100 times more sensitive to toxin than cells cultured from other adult rat tissues. Fragment A has virtually no cytotoxicity for any mammalian cell line tested.