SPLENOCYTES FROM NON-OBESE-DIABETIC MICE BINDING TO XENOGENEIC BETA-CELLS IN-VITRO AN EARLY MARKER OF CELL-MEDIATED-IMMUNITY

In as much as Type 1 diabetes is a T-cell mediated autoimmune disease, the valuation of cell mediated immunity would be useful for the study of its prodromal period. We have previously reported an increased bin ding of T splenocytes with alpha beta receptors from NOD mice to xenog eneic rat insulinoma (RIN) cells. Our present aim was to study this ph enomenon in a large number of NOD mice (n = 243) of both sexes and at different ages, together with insulitis, islet cell antibodies (ICA), and insulin autoantibodies (IAA), in order to assess their respective timing of onset, prevalence, and changes during the natural history of the disease. The number of RW-adherent splenocytes was higher (p<0.00 1) in NOD mice than in several control strains and than in F1 mice (NO D x BALB/c) which did not develop diabetes or insulitis. The increased number of RLN-adherent splenocytes in NOD mice is called ''diabetic r osettes'', and positivity is defined as a value of RIN-adherent spleno cytes higher than the mean + 2SD of control mice. The prevalence of '' diabetic rosettes'' in NOD mice was 56 %. Females displayed higher num bers of RIN-adherent splenocytes and a higher prevalence of ''diabetic rosettes'' (70 % vs 45 %) than male NOD mice (p<0.03). Using haematox ylin-eosin staining, marked insulitis became detectable after 30 days of age, with a prevalence reaching 100 % after 120 days and a severity which was higher in female than in male mice (p<0.01). ''Diabetic ros ettes'' were detectable before 30 days of age (prevalence : 37,5 %), r eached a maximum between 60 and 90 days (prevalence : 76 %) (p<0.001), and decreased in older mice (12,5 %). At the individual level in the overall NOD population, qualitative and quantitative correlations (p<0 .01) were observed between RIN-binding splenocytes and insulitis grade . IAA were detectable before 30 days of age (prevalence : 33 %) and in creased up to 65 % at the cut-off of the study (p<0.01). A weak staini ng for ICA was first observed by day 30. The ICA prevalence increased up to 120 days (65 % ; p<0.01) and decreased in older mice (45 %). Bet ween 30 days and 120 days of age, female NOD mice displayed higher num bers of RIN-adherent splenocytes or prevalence of ''diabetic rosettes' ' than male (p<0.03), while no significant difference in ICA or IAA wa s observed between both sexes. Throughout life span, the highest conco rdance rate was found between ICA and ''diabetic rosettes'' (80 %). Di abetes occurred in 15 % of male and in 65 % of female NOD mice. Ninety percent of newly-diagnosed diabetic mice displayed both ''diabetic ro settes'' and ICA, while no animal displayed diabetes without either '' diabetic rosettes'' or ICA. The prevalence of IAA and the concordance between IAA and ''diabetic rosettes'' or ICA were lower. Ten days afte r the diagnosis of diabetes, the prevalence of all markers and the con cordance rates were decreased (p<0.01), but the concordance between '' diabetic rosettes'' and ICA (40 %) remained the highest. We conclude t hat the increased binding of NOD splenocytes to RIN cells represents a n early marker of cell-mediated immunity, at least as early as ICA and IAA and preceding the marked insulitis process. The prevalence and co ncordance rates of the different markers throughout the life in both s exes and in diabetic animals indicate that ''diabetic rosettes'' prese nt kinetics in shape with the intensity of the autoimmune process duri ng the natural history of diabetes, and suggest that concordance for t his marker and ICA may be of better predictive value than any given ma rker alone.