Regulatory role of macrophages in tumor allograft development

In the study of the role of macrophages in antitumor immune response the model of Sa I (H-2a) allograft development in B10 mice (H-2b) treated with xenogenous antithymocyte serum (ATS) was used. In the treated recipients tumor growth was enhanced as compared to untreated mice, subsequently in some of the mice the tumor permanently regressed while in the rest the temporary regression was followed by a secondary progressive growth. To determine the role of macrophages at different periods of tumor development, both silica (which is known to damage the function of macrophages) and double-stranded RNA (dsRNA; which, in turn, stimulated their function), were used. The administration of silica on the day of tumor cell transplantation slightly promoted tumor regression, whereas silica administered on days 7 or 14 after the cell transfer enhanced the secondary growth of the tumor. On the other hand, administration of dsRNA on the day of tumor transplantation promoted tumor growth, whereas, when administered on days 7 or 14, it enhanced the regression of the tumor. An administration of both substances at later periods had no effect on the growth of the tumor. From these results it can be assumed that macrophages at the time of induction of antitumor immune responses participate in the events enhancing the subsequent growth of the tumor allograft, whereas at later times they have an antitumor activity.