Prior investigations from this laboratory have demonstrated that, when bone marrow cells (BMC) from a tumorbearing host are cultured, enhanced macrophage colony production occurs and macrophages from the colonies (CMA) are cytotoxic to tumor cells. The presently reported findings indicate that the cytotoxicity of CMA is highly specific, destroying only cells derived from the immunizing tumor. They support prior observations indicating that the cytotoxicity of the mature macrophage is derived from precursor stem cells and that no peripheral lymphocyte-antigen interaction with the macrophage is required for it to obtain that property. Information is also provided that indicates that cells from lymph nodes regional to a tumor (RLN) may affect stem cells from which CMA are derived. Not only is there decreased macrophage colony production when regional lymph nodes are absent, but also cytotoxicity of the resultant CMA is reduced. Observations indicating that transfer of regional lymph node cells from tumor-bearing mice to normal mice results in the production of cytotoxic CMA by BMC derived from the latter afford further support to this consideration. Findings also indicate that the cytotoxicity of CMA, like that of regional lymph node cells and BMC, is inhibited by serum from tumor-bearing animals and that the degree of inhibition increases with duration of tumor growth in the serum donor. Finally, it was observed that, with progressive tumor growth, BMC result in CMA with decreased cytotoxicity.

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Supported by USPHS Grants CA-12102 and CA-14972.

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