Thermal injury functionally alters bone marrow-derived macrophages: a study of monocyte-hepatocyte interactions

Thermal injury quantitatively and qualitatively alters hematopoiesis, including monocyte-macrophage lineage changes, resulting in altered mononuclear cell function. These bone marrow cells (BMCs) ultimately become fixed tissue macrophages (e.g., Kupffer cells). To study the effects of thermal injury on macrophage-hepatocyte interactions, rat BMCs were isolated 24 hours after burn injury, and myelopoiesis was induced by 7-day culture in granulocyte-macrophage colony-stimulating factor. Separate cultures included inflammatory mediators with growth factor function (IL-6 or PGE2). Cultured cells were incubated up to 96 hours with isolated normal hepatocytes (+/- lipopolysaccharide stimulation). The 96-hour exposure to postburn BMCs produced less of the acute phase proteins (APPs), C3 and transferrin, but more cytotoxicity as measured by 1-lactate dehydrogenase release. Sham BMCs cultured with added IL-6 caused higher APP release and minimal cytotoxicity, whereas burn BMCs stimulated lower APP release and retained cytotoxicity. In conclusion, myeloid cells regulate APP synthesis differently after thermal injury and may become more cytotoxic to hepatocytes.