Heat shock protein 27 inhibits apoptosis in human neutrophils

Background. Prolonged neutrophil(PMN) survival has been implicated in tissu e injury following sepsis. A variety of bacterial products have been identi fied which inhibit PMN apoptosis including lipopolysaccharide(LPS). Extrace llular heat shock proteins(Hsp) have recently been identified as potent reg ulatory signals for the innate immune system during the inflammatory respon se. We hypothesized that Hsp 27 can affect PMN phenotype with respect to ap optosis and cytokine profile. Materials and methods. PMN were isolated from the peripheral blood of healt hy human volunteers by red blood cell sedimentation and gradient centrifuga tion. Cells were placed in media and cultured for 18 h with and without rec ombinant human Hsp 27 at various concentrations. In parallel experiments, P MN were stimulated with LPS, a known inhibitor of PMN apoptosis, for compar ison. Apoptosis was quantified using annexin V and propidium iodide stainin g with flow cytometric analysis. Culture supernatants were assayed for secr etion of TNF-alpha, IL-10, and IL-12. Results. Hsp 27 significantly inhibits PMN apoptosis [control; 81.8 +/- 3.6 %, vs Hsp 27, 60.4 +/- 4.1% p < 0.05]. The reduction is similar to that sig naled by LPS, alone. Together their effect is not synergistic. The Hsp 27 r esponse is dose-dependent. Hsp 27 does not induce secretion of TNF-<alpha>, IL-10, or IL-12, whereas LPS does signal IL-12 and TNF-alpha secretion. Conclusion. These data demonstrate that exogenous Hsp 27 may play a role in neutrophil-mediated tissue injury during trauma and sepsis via its ability to inhibit neutrophil apoptosis. However, Hsp 27 does not significantly al ter neutrophil phenotype with respect to cytokine production profile. (C) 2 001 Academic Press.