POST-TRAUMATIC OSTEOMYELITIS: PRIMING FOR SUPEROXIDE GENERATION AS MECHANISM OF THE LOCAL TISSUE DESTRUCTION?

Abstract

Introduction: Posttraumatic osteitis is a localised inflammatory process leading to tissue destruction and eventually osteolysis. The molecular mechanisms underlying the disease progress are not yet fully understood. In a previous study we demonstrated infiltration of polymorphonuclear neutrophils (PMN) into the site of infection; the PMN were highly activated as seen by upregulation of the activation-associated surface receptors CD14 and CD64. In this study we analysed the superoxide generation by the infiltrated PMN as possible pathomechanism of the local tissue destruction.

Material and Methods: Ten patients with device-associated osteomyelitis requiring surgery were recruited into the study. When removing the infected implant the site was rinsed intraoperatively. The leukocytes were recovered, then activation-associated surface receptors were determined by cytofluorometry as was superoxide generation by reduction of cytochrome C.

Results: 1–2 x 10⁷ leukocytes were recovered from the «lavage» fluid; 80 to 90% were identified as PMN. The PMN were highly activated as seen by an upregulation of CD14 and CD64, and a concomitant downregulation of the selectin CD62L. In response to phorbol ester (PMA) the superoxide production of the infiltrated PMN was enhanced when compared to peripheral PMN of the same patient. The infiltrated PMN, but not the PMN of the peripheral blood, responded to the bacterial peptide f-Met-Leu-Phe (f-MLP) with superoxide production, indicating an enhanced responsiveness of the cells. The underlying molecular mechanisms were analysed in vitro using PMN of healthy donors: only the induction of superoxide production by f-MLP, but not by PMA, required a «priming» of the cells, for example by low doses of lipoploysaccharide (LPS) or cytokines (e.g. TNFa, IL-8).

Conclusions: In posttraumatic osteomyelitis PMN infiltrate the infected site; they are locally activated as seen by an upregulation of the appropriate receptors and by “priming” for superoxide generation. Priming of local PMN could on one hand potentiate the bactericidal activity, on the other hand contribute to tissue destruction. The occurrence of viable bacteria and activated «armed» PMN at the same site points to an esacpe mechanism, possibly due to biofilm formation. Due to their cytotoxic and proteolytic potential PMN might participate in local tissue destruction and osteolysis.