Transforming growth factor-beta negatively modulates T-cell responses in sepsis

Sepsis is associated with depressed T-cell functions and increased circulating levels of immunosuppressive agents, TGF-beta is a potential anti-inflammatory cytokine that can modify T-cell growth and differentiation. The up-regulation of TGF-beta and the mechanism of its action on the T-cells during septic injury have not been resolved, We hypothesized that in sepsis TGF-beta produced by macrophages acts on T-cells in a paracrine manner to suppress interleukin (IL)-2 production and proliferation, In this study, we examined the circulating TGF-beta levels in a rat model of Gram-negative bacterial sepsis, and compared the abilities of adherent and non-adherent splenocytes to produce TGF-beta, Additionally, we investigated the causal relationships of hrTGF-beta to concanavalin A (ConA)-induced T-cell responses and the intracellular mechanism of the generation of these responses in normal splenic rat T-cells, Sepsis was induced in rats by intraabdominally implanting fecal pellets containing Escherichia coli (150 CFU) and Bacteroides fragilis (10 000 CFU), Adherent and non-adherent splenocytes were isolated by differential adherence using Ficoll gradient centrifugation, T-cells were purified by use of Nylon wool columns, We observed a 3-6-fold increase in the circulating levels of TGF-beta in sepsis. Western blots and ELISA determinations revealed a 2.5-3-fold increase in cell-associated TGF-beta protein levels in adherent splenic cells, Northern analyses also showed a marked increase in TGF-beta mRNA expression in adherent cells during sepsis, On the other hand, a significant change was not observed in the TGF-beta protein and mRNA expression in non-adherent splenocytes, Prehreatment of control rat T-cells with hrTGF-beta decreased both ConA-induced proliferation (by 35-40%) and IL-2 mRNA expression (by > 50%), Further, whereas incubation of control rat T-cells,vith either ConA or TGF-beta for 24 h resulted in a 10-15-fold increase in cAMP generation, the addition of hrTGF-beta along with ConA resulted in a 50-60-fold increase in cAMP, These results suggest that in sepsis, TGF-beta produced by splenic macrophages can act in a paracrine manner on T-cells to depress their IL-2 mRNA expression, IL-2 production and proliferation after up-regulation of cAMP which can interfere with T-cell signaling for proliferation.