MURINE MARROW STROMAL RESPONSE TO MYELOTOXIC AGENTS IN-VITRO

Previous studies have shown that the haemopoietically active murine lo ng-term bone marrow culture (LTBMC) is a useful model for studying dru g-induced suppression and recovery of myelopoiesis. We studied the eff ects on stromal morphology and stromal progenitors, assessed as colony forming unit-fibroblasts (CFU-F), of the addition of either the antim etabolite methotrexate (MTX) or the betalactam ceftazidime (CEF) to LT BMC. The examination of 500 mu g/ml CEF-treated cultures revealed a st roma that appeared empty, with modest reduction in total stromal count s, and significant decreases in fat-containing and endothelial cells. In contrast, treatment with 1 mu M MTX for I week initially caused min imal morphologic stromal changes, thereafter total stromal cell count as well as fibroblastoid. endothelial, fat containing and macrophage c ells significantly increased. Haemopoiesis and the stroma recovered. B oth CEF and MTX reversibly suppressed stromal progenitor cells in LTBM C. When added directly to CFU-F cultures, the concentrations resulting in a 50% colony growth inhibition were 214 mu g/ml for CEF and 375 nM for MTX. These results suggest that CEF, but not MTX, has direct toxi c effects on the stroma of established LTBMC. Stromal cell increase fo llowing MTX treatment probably indicates a stromal response that may c ontribute to haemopoietic cell recovery.