SummaryIn previous studies we showed that a chronic colitis associated with a Thl T cell response can be induced by the rectal administration of the haptenizing reagent 2,4,6-trinitrobenzene sulfonic acid (TNBS). We report here that oral administration of haptenized colonic proteins (HCP) before rectal administration of TNBS effectively suppresses the ability of the latter to induce colitis. This suppression (oral tolerance) appears to be due to the generation ofmucosal T cells producing TGF-[3 and Th2-type cytokines after oral HCP administration. Peyer's patch and lamina propria CD4+ T cells from HCP-fed animals stimulated with anti-CD3/anti-CD28 had a 5-10-fold increase in their production of TGF-[3 and secreted increased amounts oflL-4 and IL-10 but lower levels oflFN-~ in comparison to T cells from ovalbumin-fed control animals. In addition, the colons of HCP-fed mice showed strikingly increased TGF-[3 but decreased IL-12 expression by immunohistochemicat studies and isolated mononuclear cells from HCP-fed animals secreted less IL-12 heterodimer. Finally, and most importantly, the suppressive effect of orally administered HCP was abrogated by the concomitant systemic administration ofanti-TGF-[3 or rlL-12 suggesting a reciprocal relationship between IL-12 and TGF-[3 on tolerance induction in TNBS-induced colitis. In parallel studies we demonstrated that TNBS-induced colitis can be transferred to naive recipient animals with purified CD4+ T cells from the colon of TNBS-treated animals and that such animals develop lethal pancolitis when exposed to very low doses of TNBS. Feeding of HCP suppressed this sensitivity to TNBS, indicating that oral feeding can suppress the response of pre-committed T cells in vivo. These studies suggest for the first time that TGF-[3 production can abrogate experimental granulomatous colitis even after such colitis is established, and thus, that regulation of TGF-[3 levels may have relevance to the treatment of human inflammatory bowel disease.

Severe-combined immune deficient (SCID) mice have been found to resist infection with the intracellular protozoan parasite Toxoplasma gondii via interleukin (IL)-12 stimulation of interferon (IFN)-gamma production by natural killer (NK) cells. Previously, we demonstrated the presence of increased levels of transcripts for transforming growth factor-beta (TGF-beta) in the brains and lungs of SCID mice infected with T. gondii, leading us to investigate the role of TGF-beta in the mechanism of resistance to T. gondii in these mice. Stimulation of splenocytes from SCID mice with heat-killed T. gondii resulted in production of low levels of IFN-gamma and a two to threefold increase in levels of TGF-beta in the culture supernatants. Production of IFN-gamma in these cultures was increased three to fourfold by addition of anti-TGF-beta antibody. Stimulation of splenocytes from SCID mice with IL-12 in combination with either TNF-alpha or IL-1 beta resulted in production of high levels of IFN-gamma. Addition of TGF-beta to these cultures inhibited production of IFN-gamma in a dose-dependent manner. Immunohistochemical studies revealed increased levels of TGF-beta protein in the spleens of SCID mice 5 days after oral infection with the ME49 strain of T gondii, and brains of SCID mice at 18 days post-infection. However, no difference was detected in the levels of TGF-beta transcripts in the spleens of uninfected mice or mice infected for 5 days. To test whether TGF-beta could antagonize IL-12 mediated resistance to T. gondii in vivo, we administered TGF-beta to SCID mice infected with T. gondii. This treatment resulted in earlier mortality of infected mice and significantly reduced the ability of exogenous IL-12 to delay time-to-death. Administration of anti-TGF-beta to SCID mice, beginning 24 h prior to infection and every 2 days thereafter, delayed significantly time-to-death. Together, our data demonstrate that TGF-beta antagonizes the ability of IL-12 to stimulate production of IFN-gamma by splenocytes from SCID mice, and suggest a role for TGF-beta in regulation of T cell-independent resistance to T. gondii.

SummaryInfection 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 immunosuppresive 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/Ipr) mouse. Our previous study implicated transforming growth factor ~ (TGF-/$) in a novel acquired defect in neutrophil function in MRL/lpr but not congenic MRL/Mp-+/+ (MR.L/n) mice (Gresham, H.D., C.J. Ray, and F.K. O'Sullivan. 1991.j. Immunol. 146:3911.) We hypothesized from these observations that MRL/lpr mice would have defects in host defense against bacterial infection and that they would have constitutively higher local and systemic levels of active TGF-/~ which would be responsible, at least in part, for the defect in host defense. We show in this paper that spontaneous elaboration of active TGF-/$ adversely affects host defense against both gram-negative and gram-positive bacterial infection in MRL/1pr 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 MR1/lpr mice fail to migrate to the site of infection during the initial stages of infection, that MR.L/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-/51 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-fi. These data indicate that elaboration of TGF-fi 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.