Biphasic depression of macrophage function after tumor transplantation

Tumor bearing produces a biphasic depression of macrophage inflammatory responses. Macrophage accumulation was measured on nitrocellulose filters in DA rats transplanted with a DMBA-induced fibrosarcoma and in SJL/J mice transplanted with a first-generation histiocytic lymphoma. The early phase defect was observed 2-5 days and 4-12 days after tumor transplantation in rats and mice respectively. Although transient, its duration could be prolonged by increasing the number of tumor cells injected. An interval of normal responses separated this early defect from a second or late-phase defect which began midway in the clinical course and persisted until death. Transplantation of syngeneic liver cells increased macrophage responses in DA rate but had no effect in SJL/J mice. The demonstration of a biphasic anti-inflammatory effect following tumor transplantation suggests that low doses of tumor cells are effective in inhibiting macrophages and that tumor bearing may alter macrophage responses by more than one mechanism.