Th2 Cytokines Have a Partial, Direct Protective Effect on the Function and Survival of Isolated Human Islets Exposed to Combined Proinflammatory and Th1 Cytokines

Studies in rodents have suggested that Th2 and Th3 cytokines can be effective in reducing proinflammatory and Th1 cytokine-induced islet damage. Whether this is the case with human islets and might be due to a direct action of Th2 and Th3 cytokines is not known. In the present study, we evaluated whether Th2 (500 U/ml IL-4 plus 100 U/ml IL-10) or Th3 (5 ng/ml TGF-1β) cytokines may prevent the derangements induced on isolated human islets by prolonged (12 or 72 h) exposure to combined proinflammatory (50 U/ml IL-1β, 1000 U/ml TNF α) and Th1 (1000 U/ml interferon γ) cytokines. Compared with control islets, cells preincubated for 12 or 72 h with proinflammatory and Th1 cytokines showed a significant decrease of glucose-stimulated insulin secretion and a significant increase of nitrites production. The addition of IL-4 plus IL-10 or TGF-1β in the medium prevented these cytostatic effects in the 12-h incubation experiments, but not after the 72-h exposure period. IL-1β, interferon γ, and TNF α caused no major change in either islet cell survival or Bcl-2 and Bax mRNA expression after a 12-h incubation; however, a marked increase in the amount of dead cells, with a major decrease of Bcl-2 mRNA expression, was observed after 72 h. The presence of Th2, but not of Th3, cytokines significantly reduced β-cell death, without any major effect on Bcl-2 and Bax mRNA expression. These results suggest that Th2 and (at lower extent) Th3 cytokines may have a partial, direct protective effect on isolated human islets exposed to the cytostatic and cytotoxic action of proinflammatory and Th1 cytokines.