Some plasma component is essential for IL-6 secretion by neutrophils

Recently, the neutrophil has been shown to have the capacity to produce a number of cytokines. Among these cytokines, interleukin-1 (IL-1), tumor necrosis factor-α (TNF-α) and IL-6 are typical examples of multifunctional cytokines involved in regulation of the immune response and inflammation. However, there are conflicting reports in the literature concerning the issue of whether IL-6 expression can be modulated in human neutrophils. In this study, we showed the spontaneous secretion of IL-1β, TNF-α and IL-6 by neutrophils. IL-6 secretion of neutrophils was effectively induced by IL- 1β. However, spontaneous or IL-1β induced secretion of IL-6 was observed only when the cells were cultured in autologous plasma. Then we examined the spontaneous secretion of cytokines by co-cultured leukocytes (neutrophils, monocytes, and lymphocytes). Surprisingly, IL-6 was dramatically secreted by the leukocytes only when the cells were cultured in autologous plasma, although IL-1β and TNF- α were secreted by the cells either in RPMI 1640 or in plasma. These observations suggest that the regulation of IL-6 production is qualitatively different from the production of IL-1β or TNF- α by leukocytes.