Monocytes in Type 1 diabetes families exhibit high cytolytic activity and subset abundances that correlate with clinical progression
Monocytes are immune regulators implicated in the pathogenesis of Type 1 diabetes (T1D), an autoimmune disease that targets the insulin-producing pancreatic ß-cell.  We determined that monocytes of recent onset (RO) T1D patients and their healthy siblings express proinflammatory/cytolytic transcriptomes and hyper-secrete cytokines in response to lipopolysaccharide exposure compared to unrelated healthy controls (uHC).  Flow cytometry measured elevated circulating abundances of intermediate monocytes and >2-fold more CD14+CD16+HLADR+KLRD1+PRF1+ NK-like monocytes among ROT1D patients compared to uHC.  The intermediate to nonclassical monocyte ratio among ROT1D patients correlated with the decline in functional ß-cell mass during the first 24 months post-onset.  Among sibling non-progressors, flow cytometry measured temporal decreases in the intermediate to nonclassical monocyte ratio and NK-like monocyte abundances; these changes coincided with increases in peripheral activated regulatory T-cells.  In contrast, these monocyte populations exhibited stability among T1D progressors.  This study associates heightened monocyte proinflammatory/cytolytic activity with T1D susceptibility and progression and offers insight to the age-dependent decline in T1D susceptibility. Overall design: Cryopreserved PBMC samples of 8 age-matched subjects (2 well-controlled ROT1D patients, 2 HRS, 2 LRS, 2 uHC) were thawed and incubated with the fixable Live/Dead Violet dye (Life Technologies, Grand Island, NY, USA),  generate a monocyte-enriched, single cell, PBMC population and analyzed by scRNA-seq.