Proinflammatory cytokine production by human peripheral blood mononuclear cells stimulated with cell-free supernatants of viridans streptococci

Viridans streptococci (VS) have become recognized as an increasingly important cause of bacteraemia in neutropenic patients undergoing chemotherapy. Surprisingly, VS bacteraemia is associated with toxic shock-like syndrome (TSLS) and adult respiratory distress syndrome (ARDS), features not seen in non-neutropenic patients with viridans streptococcal bacteraemia. The mechanism by which these Gram-positive bacteria cause hypotension in the absence of endotoxin is not known. In this study, we have analysed the ability of cell-free bacterial supernatants derived from VS to induce the production of a number of cytokines from human peripheral blood mononuclear cells (PBMC). These cytokines were tumour necrosis factor α (TNF-α), tumour necrosis factor β (TNF-β) and interleukin 8 (IL-8). All 59 strains were able to induce these proinflammatory cytokines. We conclude that VS do produce secreted products which are able to stimulate the production of cytokines which may be important in the pathogenesis of shock caused by these bacteria