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 cells which can be activated by defined signals. Here, we directly compare the release of chemokines and monokines by BMM raised either in serum-supplemented or in serum-free medium in response to Listeria monocytogenes EGD or Mycobacterium bovis BCG infection. We focused on this issue because there have been several controversial reports on the production of cytokines by BMM due to different in vitro culture conditions. Culture in serum-supplemented medium primed BMM for release of monocyte chemoattractant protein (MCP)-1, interleukin (IL)-6, and IL-12, but had no effect on macrophage inflammatory 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 higher 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 of serum could be partially mimicked by interferon-gamma. Because the serum components responsible for BMM priming are undefined, BMM cultured under serum-free conditions provide an appropriate cell population for defining macrophage activating signals.