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 (10000 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. Pretreatment 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 with 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.
Ahmad
S
S
Department of Physiology, Stritch School of Medicine, Loyola University Chicago, Maywood, IL 60153, USA.
Choudhry
M A
MA
Shankar
R
R
Sayeed
M M
MM
D000818:Animals; D016470:Bacteremia / Q000276:immunology*; D001442:Bacteroides Infections / Q000276:immunology; D001441:Bacteroides fragilis; D002448:Cell Adhesion; D003208:Concanavalin A; D000242:Cyclic AMP / Q000378:metabolism; D004797:Enzyme-Linked Immunosorbent Assay; D004927:Escherichia coli Infections / Q000276:immunology; D007376:Interleukin-2 / Q000096:biosynthesis; D008213:Lymphocyte Activation; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D012016:Reference Values; D013154:Spleen / Q000276:immunology; D013601:T-Lymphocytes / Q000187:drug effects / Q000276:immunology*; D014158:Transcription, Genetic / Q000187:drug effects; D016212:Transforming Growth Factor beta / Q000096:biosynthesis / Q000494:pharmacology / Q000502:physiology*
D007376:Interleukin-2; D016212:Transforming Growth Factor beta; D003208:Concanavalin A; D000242:Cyclic AMP