Distribution of Innate Lymphoid Cell populations in blood in different inflammatory phenotypes of asthma

<b>Introduction:</b> Innate lymphoid cells (ILC) are a group of immune cells that mirror Th-cell functions but lack specific antigen receptors. Type 2 ILCs are increased in atopic asthma compared to healthy control subjects, but data on non-atopic and non-eosinophilic asthma are lacking. <b>Aim:</b> To report the distribution of ILC subpopulations in blood according to inflammatory phenotypes of asthma <b>Methods:</b> Peripheral blood mononuclear cells were isolated from n=22 non-smoking stable asthmatics treated with ICS. Data on atopy, lung function, blood differential count, FeNO and induced sputum were obtained. Viable circulating ILC1 (lin-CRTH2-CD127+), ILC2 (lin-CRTH2+CD127+) and ILC3 (lin-CRTH2-CD127+CD117+CD56+/-) were expressed as fractions of total blood lymphocytes. Patients were stratified based on blood eosinophils (≥0.3), sputum eosinophils (≥3%), sputum neutrophils (&gt;61%) and atopy (positive skin prick test). <b>Results:</b> ILCs constituted a minor fraction of the total lymphocyte pool in peripheral blood: ILC1 0,024% (0.002-0.94%), ILC2 0.009% (0.001-0.079%), ILC3 0.033% (0.002-0.125%). No significant differences were found in ILC1 or ILC2 fractions when comparing eosinophilic and non-eosinophilic asthma whereas ILC3 was significantly higher in non-eosinophilia (Mann-Whitley P=0.04). When comparing atopic and non-atopic individuals no significant differences were found in any ILC populations, the same was true stratifying on sputum neutrophils or eosinophils. ILC3 fractions significantly correlated with the fractions of ILC2 (rho (S)=0.67, p=0.001), no correlation between remaining ILC subsets. <b>Conclusion:</b> Elevated blood ILC3 fractions may be associated with a non-eosinophilic asthma phenotype