Effects of lipopolysaccharide on a macrophage-like cell line (HS-P) from a rat histiocytic sarcoma.

Lipopolysaccharide (LPS) is a major modulator of macrophage functions. To characterize a newly established rat histiocytic sarcoma-derived cell line (HS-P), immunophenotypic changes and cellular growth responses of HS-P cells exposed to LPS were investigated and compared with those of MT-9 cells isolated from a rat malignant fibrous histiocytoma. MT-9 cells have somewhat histiocytic features, because occasional cells react to rat macrophage-specific antibodies. Addition of LPS to cultured HS-P cells increased the numbers of cells immunopositive to ED1 (rat macrophage-specific antibody) and ED2 (rat histiocyte-specific antibody) and stimulated the phagocytosis of latex beads, whereas LPS-treated MT-9 cells did not show such immunophenotypic changes. LPS-treated HS-P cells showed enhanced immunolabelling of alpha-smooth muscle actin, suggesting a possible modulation of macrophages towards myofibroblastic cells. To evaluate cellular growth after the addition of LPS or fetal bovine serum, DNA synthesis was examined by measuring tritiated thymidine incorporation, and the mRNA expression of c- jun and c- myc (immediate early genes in the cell cycle) was examined by Northern blot analysis. In HS-P cells, the addition of serum greatly increased DNA synthesis and induced high expression of c- jun and c- myc; in contrast, LPS markedly depressed DNA synthesis and reduced the expression of c- jun and c- myc. HS-P cells were more sensitive than MT-9 cells to the growth-promoting effect of serum and the growth-inhibiting effect of LPS. The study demonstrated that HS-P cells are highly LPS-responsive, indicating that they would be useful for studies of macrophage functions.