Neonatal injections of cyclosporin enhance autoimmune diabetes in non-obese diabetic mice

SUMMARY Since the modulation of the immune system at birth may influence the course of insulin-dependent (type 1) diabetes, we investigated whether neonatal injections of cyclosporin (CsA) to newborn non-obese diabetic (NOD) mice influence diabetes during later life. Two groups of 90 mice (45 female, 45 male) were injected intraperitoneally for the first 6 days of life with CsA (l0mg/kg per day) or with vehicle. In female NOD mice, the onset of diabetes was earlier and cumulative incidence was higher after neonatal treatment with CsA (P < 0·01). The incidence of diabetes was also dramatically enhanced in male NOD mice (P < 0·01), which normally display a very low disease incidence. Concomitantly, the severity of lymphocytic infiltration of the pancreatic islets was higher in female NOD mice neonatally treated by CsA (P < 0·02), and to a lesser extent in males, than in control mice. After administration of CsA to newborn NOD mice, there was a reduction (P < 0·01) of both CD4+CD8+ and CD4+CD8+ thymocytes, whereas the number of double positive CD4+CD8+ thymocytes was increased. Concomitantly, Thy 1–2+ cells in spleen were decreased (P < 0·01), and spleen cells expressing either CD3 molecule or αβ TCR complex were diminished (P < 0·01). Both CD4+ and CD8+ spleen T cells were depleted. By contrast, the low percentage of γδ TCR-expressing splenocytes was not modified. Numbers of MHC class 1+ or MHC class 2+ spleen cells were also depressed (P < 0·01). After neonatal injections of CsA, spleen cells showed a reduced response to concanavalin A (Con A) (P < 0·01). On the contrary, stimulation indices of splenocytes incubated with xenogeneic insulin-producing cell extracts were enhanced (P < 0·03). Proliferation indices of splenocytes to self class 2 antigens, generating suppressor cell activity, during syngeneic mixed lymphocyte reaction (SMLR) were significantly reduced (P < 0·01). Irradiated NOD mice were used as recipients for spleen cells from CsA -neonatally treated NOD mice. They displayed enhanced insulitis 2 weeks after transfer, and diabetes was successfully produced by 1 month after transfer in 50% of the recipients. By contrast, NOD mice which received control syngeneic spleen cells remained normoglycaemic, with only moderate islet infiltration which would be expected of NOD mice of this age. Thus, neonatal injections of CsA markedly enhance diabetes in both female and male NOD mice. The mechanisms behind the clinical effect are at least related to arrest of thymocytopoiesis at the double positive stage and to attenuation of suppressor cell activity during the completion of immune selftolerance, leading to enhancement of autoreactive T lymphocytes directed against insulin-secreting cells. This could be a useful tool for gaining insight into both the mechanisms underlying the thymic generation of autoreactive T lymphocytes against islet cells and the peripheral immunoregulatory device that controls expansion of the disease already initiated.