CIRCULATING PLATELET-NEUTROPHIL AGGREGATES REPRESENT A PERIPHERAL BIOMARKER OF TYPE 1 DIABETES DEVELOPMENT IN NOD MICE

Background: In certain autoimmune diseases, platelets and neutrophils are engaged in a vicious cycle of activation which promotes autoimmune disease. The aim of this study was to examine the contribution of platelet-neutrophil interactions to the development of Type 1 diabetes (T1D) in NOD mice. Methods: Platelet-neutrophil aggregates (PNAs) were analysed by flow cytometry in (i) the peripheral blood of NOD female mice at 3, 4, 6-8, 10-12, 16-18 weeks of age and at T1D onset and (ii) insulitis leukocytes harvested from islets isolated from additional NOD mice at the same corresponding ages. PNAs were identified as CD41+ve (platelet marker) Ly6Clo/Ly6Ghi neutrophils. Peripheral blood of male NOD mice at 3 -18 weeks of age (with characteristic low T1D incidence) and non-autoimmune control B6.SL mice were analysed in parallel. Results: Three waves of circulating PNAs were found in female NOD mice, peaking at 4 weeks, 10-12 weeks of age and at T1D-onset. These peak PNA levels correlated with the initiation of T1D autoimmunity in young NOD mice (from 3 weeks of age), marked infiltration of islets by inflammatory leukocytes (at 10-12 weeks) and the clinical onset of T1D. In contrast, male NOD mice demonstrated an elevation in PNAs only at 4 weeks of age. Islet PNAs were found to peak in NOD females at 4 weeks and 10-12 weeks of age. Islet PNAs therefore characterised the initiation of T1D autoimmunity in NOD mice (3 weeks) and contributed to the intra-islet leukocyte influx to damage beta cells in female mice at 10-12 wks. In female NOD mice the dynamic profile of islet-associated PNAs correlated with the PNA profile in peripheral blood. These findings suggest that PNA levels in peripheral blood represent a novel biomarker of T1D development.