Ultrafiltered pig leukocyte extract (IMUNOR®) decreases nitric oxide formation and hematopoiesis-stimulating cytokine production in lipopolysaccharide-stimulated RAW 264.7 macrophages

A low-molecular-weight (< 12 kDa) ultrafiltered pig leukocyte extract, IMUNOR®, was tested in experiments in vitro on non-stimulated and lipopolysaccharide (LPS)-stimulated murine RAW 264.7 macrophages in order to assess modulation of nitric oxide (NO) production (measured indirectly as the concentration of nitrites), hematopoiesis-stimulating activity of the supernatant of the macrophage cells (ascertained by counting cell colonies growing from progenitor cells for granulocytes and macrophages (GM-CFC) in vitro), and the release of hematopoiesis-stimulating cytokines. No hematopoiesis-stimulating activity and cytokine or NO production were found in the supernatant of non-stimulated macrophages. It was found that IMUNOR® does not influence this status. Supernatant of LPS-stimulated macrophages was characterized by hematopoiesis-stimulating activity, as well as by the presence of nitrites, interleukin-6 (IL-6), and granulocyte colony-stimulating factor (G-CSF). A key role in the hematopoiesis-stimulating activity of the supernatant of LPS-stimulated macrophages could be ascribed to G-CSF since the formation of the colonies could be abrogated nearly completely by monoclonal antibodies against G-CSF. IMUNOR® was found to suppress all the mentioned manifestations of the LPS-activated macrophages. When considering these results together with those from our previous in vivo study revealing stimulatory effects of IMUNOR® on radiation-suppressed hematopoiesis, a hypothesis may be formulated which postulates a homeostatic role of IMUNOR®, consisting in stimulation of impaired immune and hematopoietic systems but also in cutting back the production of proinflammatory mediators in cases of overstimulation which threats with undesirable consequences.