Aims/hypothesis. Cytokines and chemokines are important mediators of immune responses due to their ability to recruit and activate leukocytes. Using microarray analysis we observed that rat beta cells exposed to IL-1β and IFN-γ have increased mRNA levels of chemokines and IL-15. The aim of this study was to characterize the expression of IP-10, MIP-3α, fractalkine and IL-15 in rat beta cells, human pancreatic islets, and in islets isolated from NOD mice, both during the pre-diabetic period and following islet transplantation.

Methods. FACS-purified rat beta cells and human islets were cultured with IL-1β, IFN-γ and/or TNF-α. Islets were isolated from NOD or BALB/c mice at different ages. For syngeneic islet transplantation, 2- or 3-week-old NOD islets were grafted under the kidney capsule of spontaneously diabetic NOD recipients. Chemokine and IL-15 mRNA expression and protein release were evaluated, respectively, by RT-PCR and ELISA.

Results. Human islets and rat beta cells express IP-10, MIP-3α, fractalkine and IL-15 mRNAs upon exposure to cytokines. The expression of IL-15, IP-10 and fractalkine is regulated by IFN-γ, while the expression of MIP-3α is IL-1β-dependent. Moreover, cytokines induced IL-15, IP-10, Mig, I-TAC and MIP-3α protein accumulation in culture medium from human islets. In vivo, there was an age-related increase in IL-15, IP-10 and MIP-3α expression in islets isolated from NOD mice. Following syngeneic islet transplantation, increased expression of IL-1β, IFN-γ, fractalkine, IP-10, MCP-1 and MIP-3α mRNAs were observed in the grafts.

Conclusion/interpretation. Cytokine-exposed islets or beta cells express chemokines and IL-15. This could contribute to the recruitment and activation of mononuclear cells and development of insulitis in early Type 1 diabetes and during graft destruction.