IN-VITRO INHIBITION OF INSULIN RELEASE BY BLOOD MONONUCLEAR-CELLS FROM INSULIN-DEPENDENT DIABETIC AND HEALTHY-SUBJECTS - SYNERGISTIC ACTIONOF IL-1 AND TNF

Previous studies have demonstrated that peripheral blood mononuclear c ells (BMC) from type 1 (insulin-dependent) diabetic patients inhibit i nsulin release (IR) from rat or mouse islet cells in vitro. This pheno menon is of great interest as a model for islet graft rejection. We fo und that lipopolysaccharide (LPS)-stimulated BMC of healthy donors and type 1 diabetic patients suppress both basal and stimulated insulin s ecretion. To study whether this inhibition was due to soluble mediator s we added supernatants of LPS-stimulated BMC or recombinant human int erleukin-1beta (IL-1) and tumor necrosis factor-alpha (TNF) at concent rations comparable to those found in the supernatants to rat islet cel ls. The inhibitory effect of BMC on islet cells could be transferred b y supernatants of LPS-stimulated BMC. We found that neither IL-1 nor T NF alone inhibit IR from dispersed adult rat islet cells. However, the combination of IL-1 and TNF was highly effective. Ultrafiltration of supernatants of LPS-stimulated BMC through a PM-10 membrane (10 kDa cu toff ) deprived the supernatants of the inhibitory activity indicating that only intact IL-1 and TNF (m.w. about 17 kDa), but not smaller IL -1 and TNF fragments, were responsible for the effects on islet cells. These data suggest that activation of BMC and cytokine release at isl et graft site may result in an early loss of graft function. Islet tra nsplantation using microcapsules not permeable for molecules with m.w. > 10 kDa would be preferable.