Streptococcus equi but not Streptococcus zooepidemicus produces potent mitogenic responses from equine peripheral blood mononuclear cells

Streptococcus equi causes equine strangles. The acute disease has many of t he hallmarks of an acute response including high fever, elevated plasma fib rinogen and neutrophilia, affects known to be mediated by proinflammatory c ytokines. The objective of this study was to screen-culture supernatants fr om equine clinical isolates of S. equi and S. zooepidemicus for stimulation of mitogenic responses by horse peripheral blood mononuclear cells. Mitoge nicity comparable to that of concanavalin A was detected in culture superna tants of S, equi strains but not in those of S. zooepidemicus. Mitogenicity was neutralised by Proteinase K and a post-strangles convalescent serum, a nd evidence for the presence of both thermo-resistant and thermo-labile mit ogenic factors was obtained. Release of proteinaceous immunogenic mitogens in combination with the antiphagocytic protein SeM unique to S. equi may th erefore contribute to some of the severe clinical manifestations of acute s trangles in the horse. (C) 1999 Elsevier Science B.V. All rights reserved.