KERATINOCYTE PROINFLAMMATORY RESPONSES TO ADHERENT AND NONADHERENT GROUP-A STREPTOCOCCI

The gram-positive bacterium Streptococcus pyogenes (group A streptococ cus) is the causative agent of a wide variety of suppurative infection s of cutaneous tissues, Previous analyses have demonstrated that the M protein of S. pyogenes is an adhesin that directs the attachment of t he streptococcus to keratinocytes in the skin, In this study, we have examined keratinocyte function in response to S. pyogenes and found th at adherent versus nonadherent streptococci promote distinct patterns of expression of several proinflammatory molecules and keratinocyte ce ll fate, When analyzed by a quantitative reverse transcriptase PCR met hod, infection of cultured HaCaT keratinocytes with adherent, but not nonadherent, streptococci resulted in increased expression of mRNA for the cytokines interleukin-1 alpha (IL-1 alpha), IL-1 beta, and IL-8 b ut neither infection induced expression of tumor necrosis factor alpha , In contrast, both adherent and nonadherent S. pyogenes induced expre ssion of IL-6 and each promoted synthesis and release of prostaglandin E-2 (PGE(2)). However, considerably greater levels of IL-6 expression were stimulated by adherent streptococci relative to nonadherent stre ptococci and the kinetics of PGE(2) release in response to nonadherent streptococci was delayed compared to the response to adherent strepto cocci, Staining with the fluorescent probe ethidium homodimer-l reveal ed that keratinocyte membranes were rapidly damaged upon infection wit h adherent streptococci but were not damaged by nonadherent streptococ ci. Finally, treatments which inhibited streptococcal metabolism compl etely blocked the ability of adherent streptococci to elicit responses , These data suggest that expression of an adhesin is a strategy used by S. pyogenes to modulate keratinocyte responses during infection of the skin and implicate additional streptococcal products in these sign aling interactions.