Endogenous interferon production by endotoxin-responsive macrophages provides an autostimulatory differentiation signal

Previous studies have demonstrated that peritoneal macrophages (resident or thioglycolate-induced) derived from mouse strains fully responsive to gram-negative endotoxins continue to differentiate in vitro, as evidenced by an increased capacity to phagocytose via the Fc receptor with time in culture. In contrast, macrophages derived from endotoxin-hyporesponsive mouse strains (e.g., C3H/HeJ or C57BL/10ScN) exhibit no such increase in phagocytic capacity, and, in fact, significantly lose the capacity to phagocytose particles opsonized with immunoglobulin G with time in culture. This defect was found to be fully correctable by the addition to the cultures of an exogenous source of α, β, or γ interferon. In this study, we compared C3H/HeN (endotoxin-responsive) and C3H/HeJ (endotoxin-hyporesponsive) macrophages in an attempt to elucidate the mechanism responsible for this difference in phagocytic (differentiative) potential. The following observations support the hypothesis that endotoxin-responsive macrophages, in contrast to endotoxin-hyporesponsive macrophages, produce significantly higher levels of an autostimulatory differentiation signal that appears to be macrophage-derived interferon. (i) Anti-α/β-interferon antibody greatly reduces the ability of C3H/HeN macrophages to phagocytose opsonized erythrocytes; (ii) C3H/HeJ macrophages can be made phagocytic by coculture with C3H/HeN macrophages or by treatment with supernatants derived from C3H/HeN macrophage cultures; and (iii) C3H/HeN macrophages spontaneously lose Mac-1 antigen with time in culture. C3H/HeJ macrophages must be interferon-treated to be equivalently down-regulated.