Effect of fetal calf serum on cytokine release by bone marrow-derived macrophages during infection with intracellular bacteria

Bone marrow-derived macrophages (BMM) comprise a population of quiescent ce lls which can be activated by defined signals. Here, we directly compare th e release of chemokines and monokines by BMM raised either in serum-supplem ented or in serum-free medium in response to Listeria monocytogenes EGD or Mycobacterium bovis BCG infection. We focused on this issue because there h ave been several controversial reports on the production of cytokines by BM M due to different in vitro culture conditions. Culture in serum-supplement ed medium primed BMM for release of monocyte chemoattractant protein (MCP)- 1, interleukin (IL)-6, and IL-12, but had no effect on macrophage inflammat ory protein (MIP)-1 alpha and tumor necrosis factor (TNF)-alpha production in response to L. monocytogenes infection. After challenge infection with M . bovis, BMM raised and stimulated in serum-supplemented medium secreted hi gher levels of MCP-1, MIP-1 alpha, IL-6, and TNF-alpha but not of IL-12 as compared to BMM cultured and infected in a serum-free medium. The effects o f serum could be partially mimicked by interferon-gamma. Because the serum components responsible for BMM priming are undefined, BMM cultured under se rum-free conditions provide an appropriate cell population for defining mac rophage activating signals.