Identifying T-lymphocytes in the sputum of children with acute asthma

<b>Background:</b> Asthma frequently starts in childhood and acute severe asthma attacks are thought to contribute to the development of severe T2 driven allergic asthma. There is a lack of information regarding airway helper and cytotoxic T-lymphocytes present during an exacerbation in children. <b>Aim:</b> To compare airway inflammation in acute paediatric asthmatics with clinically stable asthmatics. <b>Methods:</b> Children aged 5-16 years old (n=15), with an acute exacerbation, were asked to produce a spontaneous sputum sample. Sputum was assessed using flow cytometry to identify cell populations including eosinophils, helper and cytotoxic T-lymphocytes, type-2 innate lymphoid cells (ILC2s) and basophils. Cell populations were compared with sputum from an unpaired ‘stable’ asthmatic cohort (n=5). Data reported as medians with interquartile range. <b>Results:</b> CD4+ helper and CD8+ cytotoxic T-lymphocyte populations were identified in the sputum of acute patients (% of CD3+ count: CD4+ 35 (26 - 51), CD8+ 40 (22 - 44)). Small populations of rare cells, such as T-lymphocyte sub-populations (peTH2 and Tc2 cells), ILC2s and basophils, were also identified. There was no significant difference in lymphocytes between acute and stable patients. Macrophages were significantly higher in stable cohort (% of live, CD45+ count: acute 1.52 (0.82 – 3.09) vs stable 24 (4.78 - 51)). <b>Conclusion:</b> A range of cell populations can be isolated from the sputum of children with acute severe asthma using flow cytometry. We found no difference in lymphocyte populations between acute and stable phase. Functional studies are required as the next step to explore drivers of acute and chronic asthma.