Spontaneous elaboration of transforming growth factor beta suppresses host defense against bacterial infection in autoimmune MRL/lpr mice

Infection with gram-negative and gram-positive bacteria remains a leading cause of death in patients with systemic lupus erythematosis (SLE), even in the absence of immunosuppressive therapy. To elucidate the mechanisms that underly the increased risk of infection observed in patients with systemic autoimmunity, we have investigated host defense against bacterial infection in a murine model of autoimmunity, the MRL/Mp-lpr/lpr (MRL/lpr) mouse. Our previous study implicated transforming growth factor beta (TGF-beta) in a novel acquired defect in neutrophil function in MRL/lpr but not congenic MRL/Mp-+/+ (MRL/n) mice (Gresham, H.D., C.J. Ray, and F.K. O'Sullivan. 1991. J. Immunol. 146:3911). We hypothesized from these observations that MRL/lpr mice would have defects in host defense against bacterial infection and that they would have constitutively higher local and systemic levels of active TGF-beta which would be responsible, at least in part, for the defect in host defense. We show in this paper that spontaneous elaboration of active TGF-beta adversely affects host defense against both gram-negative and gram-positive bacterial infection in MRL/lpr mice. Our data indicate that MRL/lpr mice, as compared with congenic MRL/n mice, exhibit decreased survival in response to bacterial infection, that polymorphonuclear leukocytes (PMN) from MRl/lpr mice fail to migrate to the site of infection during the initial stages of infection, that MRL/lpr mice have a significantly increased bacterial burden at the site of infection and at other tissue sites, and that this increased bacterial growth occurs at a time (> 20 h after infection) when PMN influx is greatly enhanced in MRL/lpr mice. Most intriguingly, the alteration in PMN extravasation during the initial stages of infection and failure to restrict bacterial growth in vivo could be duplicated in MRL/n mice with a parenteral injection of active TGF-beta 1 at the time of bacterial challenge. Moreover, these alterations in host defense, including survival in response to lethal infection, could be ameliorated in MRL/lpr mice by the parenteral administration of a monoclonal antibody that neutralizes the activity of TGF-beta. These data indicate that elaboration of TGF-beta as a result of autoimmune phenomenon suppresses host defense against bacterial infection and that such a mechanism could be responsible for the increased risk of bacterial infection observed in patients with autoimmune diseases.