Immunohistochemical, quantitative immunoelectron microscopic, and DNA cytofluorometric characterization of chemically induced rat malignant fibrous histiocytoma.

Malignant fibrous histiocytoma (MFH) was induced in rats by injection of 9,10-dimethyl-1,2-benzanthracene. Using cell suspensions prepared from the heterotransplanted nude mouse tumor as immunogen, a monoclonal antibody, (MAb), MEP-1, against fibroblastlike MFH tumor cells was generated. In the primary rat tumors and transplanted rat or nude mouse tumors, MEP-1 reacted specifically with the fibroblastlike cells but not with the histiocytelike cells or xanthoma cells. Anti-rat macrophage MAbs RM-1 and TRPM-3 did not stain the fibroblastlike cells, but both were reactive with the histiocytelike cells. Double stainings with both MEP-1 and RM-1 or TRPM-3 did not detect any double positive cells. Immunoelectron microscopy using these MAbs showed that the fibroblastlike cells were the major cell component of the primary and transplanted rat tumors and that their cell membrane was stained positively with MEP-1, but not for RM-1 or TRPM-3. By the double staining method using a MAb against prolyl 4-hydroxylase beta and MEP-1 or TRPM-3, this enzyme was demonstrated in MEP-1-positive cells but not in TRPM-3-positive cells. Results obtained by DNA cytofluorometry with 4,6-diamidino-2-phenylindole dihydrochloride staining or by the combined method of DNA cytofluorometry and indirect immunofluorescence, using MEP-1, RM-1, and TRPM-3, indicate that MEP-1-positive cells are neoplastic cells of rat MFH having proliferation activity. In the transplanted nude mouse tumors, no differentiation of MEP-1-positive rat tumor cells into histiocytelike cells was detected, and all histiocytelike cells were immunostained by F4/80 and most of them were positive for M5/114. These results suggest that fibroblastlike cells and intermediate cells are tumor cells of 9,10-dimethyl-1,2-benzanthracene-induced rat MFH showing differentiation toward fibroblasts and that histiocytelike cells are infiltrated macrophages.