The responses of B lymphocyte colony-forming cells (BL-CFC) and hematopoietic colony-forming cells (HP-CFC) to three structurally unrelated chemically highly purified bacterial cell-wall components (BCWC) were studied in vivo. The total femoral BL-CFC content in C57BL/6 mice was found to be decreased approximately 70-fold 6 days after injection of lipid A and approximately 40-fold after injection of the outer membrane lipoprotein of Escherichia coli. Murein caused a much smaller decrease. In contrast to the marrow, the total splenic BL-CFC content did not change significantly after injection of any of the three BCWC. The response pattern of HP-CFC differed completely from that of BL-CFC. Although in the marrow only slight fluctuations were observed, the total spleen content of HP-CFC increased markedly after injection of either lipid A or lipoprotein but not after murein injection.

The decreased incidence of marrow BL-CFC was found to be maximal 4 to 6 days after injection, and normal levels of marrow BL-CFC were detectable again 2 weeks after injection. Inhibitory factors produced by marrow cells, especially prostaglandin E, appear not to be responsible for the decreased B lymphocyte colony-forming capacity of post-lipid A or post-lipoprotein marrow. The frequency of immunoglobulin-positive cells was also decreased in the marrow of mice injected with BCWC, but to an extent far too low to account completely for the decreased incidence of BL-CFC.

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This work was supported by a Research Fellowship from the Deutsche Forschungsgemeinschaft, and by the Anti-Cancer Council of Victoria, the National Health and Medical Research Council, Canberra, and by Contract I-CB-74147 from the National Cancer Institute, Washington, D. C.

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