Specific passive immunotherapy of experimental lymphoma. Effects of macrophage toxic drugs.

Sub-lethal irradiation experiments have indicated that undamaged host cells are necessary for efficiency of specific passive tumour immunotherapy. To further indentify these host cells, the effect of known macrophage toxic agents (silica, carrageenan, trypan blue) were tested on passive immunotherapy of a Gross virus induced C57BL/6 mouse lymphoma with specific W/Fu rat anti-Gross cell surface antigens serum. Median survival time of serum treated mice was significantly decreased when toxic drug was injected three hours before tumour cell injection and seven hours before the beginning of passive immunotherapy, only if silica (5 mg i.p./mouse) or carrageenan (2.5 mg i.p./mouse) but not if trypan blue (4 mg i.p./mouse) was used. Pretreatment by PVNO, a macrophage protecting agent, 24 hours before, inhibited silica effect but not carrageenan effect on the passive immunotherapy. These results indicate that host's phagocytic cells are likely to be involved in the efficiency of passive antibody mediated tumour cell destruction, possibly through opsonization. However, more than one phagocyte population may participate in such a mechanism.