NEONATAL INJECTIONS OF CYCLOSPORINE ENHANCE AUTOIMMUNE DIABETES IN NONOBESE DIABETIC MICE

Since the modulation of the immune system at birth may influence the c ourse 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 mic e (45 female, 45 male) were injected intraperitoneally for the first 6 days of life with CsA (10 mg/kg per day) or with vehicle. In female N OD mice, the onset of diabetes was earlier and cumulative incidence wa s higher after neonatal treatment with CsA (P < 0.01). The incidence o f diabetes was also dramatically enhanced in male NOD mice (P < 0.01), which normally display a very low disease incidence. Concomitantly, t he severity of lymphocytic infiltration of the pancreatic islets was h igher in female NOD mice neonatally treated by CsA (P < 0.02), and to a lesser extent in males, than in control mice. After administration o f CsA to newborn NOD mice, there was a reduction (P < 0.01) of both CD 4(+)CD8(-) and CD4(-)CD8(+) thymocytes, whereas the number of double p ositive CD4(+)CD8(+) thymocytes was increased. Concomitantly, Thy1-2() cells in spleen were decreased (P < 0.01), and spleen cells expressi ng either CD3 molecule or cup TCR complex were diminished (P < 0.01). Both CD4(+) and CD8(+) spleen T cells were depleted. By contrast, the low percentage of gamma delta TCR-expressing splenocytes was not modif ied. Numbers of MHC class 1(+) or MHC class 2(+) spleen cells were als o depressed (P < 0.01). After neonatal injections of CsA, spleen cells showed a reduced response to concanavalin A (Con A) (P < 0.01). On th e contrary, stimulation indices of splenocytes incubated with xenogene ic insulin-producing cell extracts were enhanced (P < 0.03). Prolifera tion indices of splenocytes to self class 2 antigens, generating suppr essor 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. T hey displayed enhanced insulitis 2 weeks after transfer, and diabetes was successfully produced by 1 month after transfer in 50% of the reci pients. By contrast, NOD mice which received control syngeneic spleen cells remained normoglycaemic, with only moderate islet infiltration w hich would be expected of NOD mice of this age. Thus, neonatal injecti ons of CsA markedly enhance diabetes in both female and male NOD mice. The mechanisms behind the clinical effect are at least related to arr est of thymocytopoiesis at the double positive stage and to attenuatio n of suppressor cell activity during the completion of immune self-tol erance, leading to enhancement of autoreactive T lymphocytes directed against insulin-secreting cells. This could be a useful tool for gaini ng insight into both the mechanisms underlying the thymic generation o f autoreactive T lymphocytes against islet cells and the peripheral im munoregulatory device that controls expansion of the disease already i nitiated.