Analysis of the effects of lipopolysaccharide on macrophages: Differential phagocytic responses of C3H/HeN and C3H/HeJ macrophages in vitro

The phenomenon of lipopolysaccharide (LPS)-induced in vitro macrophage cytotoxicity has been reported by a number of investigators but was often been difficult to reproduce and to quantitate. In this report, we have examined the effect of LPS on the ability of macrophages to ingest ⁵¹Cr-labeled, opsonized sheep erythrocytes as a method for examining the direct toxic effects of LPS on macrophages in vitro. By using this assay, we can clearly discriminate between LPS responder C3H/HeN macrophages and LPS nonresponder C3H/HeJ macrophages and demonstrate that LPS induces a profound inhibition of Fc-mediated phagocytosis in LPS responsive macrophages. Furthermore, low concentrations of LPS stimulate phagocytosis in macrophages derived for C3H/HeJ mice. The lipid A moiety of the LPS is responsible for the observed enhancement or inhibition of Fc-mediated phagocytosis. This assay was more sensitive than LPS-induced cytotoxicity, since inhibition of phagocytosis was detectable in cultures of LPS-sensitive macrophages even when cytotoxicity, assessed by trypan blue exclusion, was not. Thus, this assay represents an extremely sensitive method for analyzing the direct effects of LPS on macrophages.