HEMATOPOIESIS IN THE PRESENCE OF MACROPHAGES IN LONG-TERM BONE-MARROWCULTURES

We have studied the role of macrophages as stromal elements in long-te rm cultures of murine bone marrow cells. Normal ectopic macrophages we re collected from the lung and co-cultured in various ratios with bone marrow cells in Dexter suspension cultures. At weekly intervals, vari ous parameters of the cultures were evaluated and compared with contro ls. Increased numbers of macrophages in the bone marrow caused a delay in the formation of the confluent stroma, with distinct differences i n the pattern of hematopoietic foci in the stroma. Cytologic analysis of nucleated cells in the nonadhering fraction showed that the monocyt ic macrophages were the eventual line of differentiation in all cultur es; however, this phenomenon was accelerated in cultures containing va rious fractions of macrophages. There was a dose-dependent reduction i n the number of myeloid progenitors in the nonadhering and adhering fr actions of macrophage-enriched cultures with respect to controls. This effect was mediated through both humoral factors released in the cult ure and direct interaction between macrophages and bone marrow cells. The results indicate that elevation of the number of macrophages in th e bone marrow could result in an impaired process of hematopoiesis.