Effects of supernatants and lysates of polymorphonuclear leucocytes: macrophage stimulatory factors.

Polymorphonuclear leucocytes (PMN) were harvested from the site of a non-specific acute inflammatory reaction. When cultured in vitro for 24 h the cells liberated into the supernatant factors which could enhance the proliferation of normal macrophages in the absence and presence of the mitogen phytohaemagglutinin (PHA). Similar activity was found in lysates of these cells. Using the technique of ultrafiltration it was shown that the mitogenic factors present in both PMN supernatants and lysates were under 10 000 daltons molecular weight. In addition, the chemiluminescent responses of normal macrophages were also enhanced by PMN supernatant, lysate and their respective ultrafiltrates. Our results suggest that the PMNs, which are the most abundant cell type during acute inflammation, both contain and are able to liberate low-molecular-weight macrophage-stimulatory factors which may be important in our understanding of the pathogenesis of inflammation.