Helper Factor{s) Generated by Tumor-lmmuneRatsfor Lymphoproliferative Responses to Syngeneic Tumor Cells 1,2,3

ABSTRACT-New Zealand Black (NBR) rats that are innately immune to challenge with a syngeneic 3-methylcholanthrene [(MCA) CAS: 56-49-51-induced fibrosarcoma have spleen cells that produce helper effects for in vitro Iymphoproliferative re-sponses in the presence of individual MCA-induced fibrosarcoma cells. Spleen cells from MCA-induced fibrosarcoma progressor rats (which lack innate tumor immunity) do not produce demon-strable helper activity. Supernatants from 48-hour cocultures of spleen cells from tumor-immune (TI) rats and syngeneic MCA-induced fibrosarcoma cells replaced the spleen cell helper activ-ity. Comparable spleen cell supernatants from tumor progressor rats or unchallenged rats (controls) as well as supernatants from MCA-induced fibrosarcoma cells cultured alone did not produce any helper factor activity. Supernatants from TI rat spleen cells following inoculation with MCA-induced fibrosarcoma cells di