Unremitting pro‐inflammatory T‐cell phenotypes, and macrophage activity, following paediatric burn injury

Abstract Objectives The aim of this study was to characterise the dynamic immune profile of paediatric burn patients for up to 18 months post‐burn. Methods Flow cytometry was used to measure 25 cell markers, chemokines and cytokines which reflected both pro‐inflammatory and anti‐inflammatory immune profiles. Peripheral blood mononuclear cells from 6 paediatric burn patients who had returned for repeated burn and scar treatments for > 4 timepoints within 12 months post‐burn were compared to four age‐matched healthy controls. Results While overall proportions of T cells, NK cells and macrophages remained relatively constant, over time percentages of these immune cells differentiated into effector and proinflammatory cell phenotypes including Th17 and activated γδ T cells. Circulating proportions of γδ T cells increased their expression of pro‐inflammatory mediators throughout the burn recovery, with a 3–6 fold increase of IL‐17 at 1–3 weeks, and NFκβ 9–18 months post‐burn. T‐regulatory cell plasticity was also observed, and Treg phenotype proportions changed from systemically reduced skin‐homing T‐regs (CCR4+) and increased inflammatory (CCR6+) at 1‐month post‐burn, to double‐positive cell types (CCR4+CCR6+) elevated in circulation for 18 months post‐burn. Furthermore, Tregs were observed to proportionally express less IL‐10 but increased TNF‐α over 18 months. Conclusion Overall, these results indicate the circulating percentages of immune cells do not increase or decrease over time post‐burn, instead they become highly specialised, inflammatory and skin‐homing. In this patient population, these changes persisted for at least 18 months post‐burn, this ‘immune distraction’ may limit the ability of immune cells to prioritise other threats post‐burn, such as respiratory infections.