(117) IL-6 and SPLUNC1 Fluctuations as Sex-Specific Markers of Acute Cystic Fibrosis Exacerbation.

Background: Women with cystic fibrosis (CF) experience increased rates of respiratory illness, lung function decline, and mortality relative to men. This clinical sexual dimorphism is partly explained by differential immune cell activation and inflammatory marker expression between sexes and across cell types. In previous work, we showed that airway inflammation markers differed between participants with and without CF and between periods of clinical stability and acute illness (exacerbation, PEx) among those with CF. Non-invasive biomarkers can identify patients at risk of PEx and guide adjustments in therapy. Here, we performed studies to define sexually dimorphic airway inflammation marker profiles in CF participants during periods of stability and PEx.

Methods: We conducted a cross-sectional study of sputum samples from two cohorts of CF subjects aged 14-79 with confirmed CF diagnosis from the Yale and University of Minnesota CF Programs (n=44, 19 male, 25 female and n=35, 16 male, 19 female, respectively). Participants were classified as "stable CF" or "PEx” based on predefined PEx criteria. Sputum samples were assayed for markers of CF airway inflammation including 13 airway cytokines and airway host defense protein Short Palate Lung Nasal epithelium Clone 1 (SPLUNC1) using ELISA. We generated receiver operator curves for SPLUNC1 and IL-6 based on stable and exacerbation values to define a cutoff value for Mantel-Haenzsel estimations of time to next exacerbation in SPLUNC1 High/Low and IL-6 High/Low groups. Finally, we performed sex-based analyses to define differences in marker levels and mean biomarker change from baseline during periods of stability and PEx.

Results: IL-1β increased (mean change from 4.6 to 9.8μg, p=0.006) and SPLUNC1 decreased (mean change from 7.7 to 1.6μg, p=0.012) during PEx in all participants with CF (Fig.1a). Low SPLUNC1 was associated with a significantly increased likelihood of PEx at 60 days, whereas increased IL-6 was not (Fig. 1b). When comparing our panel of 14 airway markers of inflammation between male and female participants, only IL-6 was consistently increased in males in both stable and PEx states (p=5.47x10^-5, 9.10x10^-10 respectively, Fig. 1c). Interestingly, the male-female differential between mean cytokine levels widened ( >71.8% of mean value) during PEx for cytokines CXCL10, TNFα, G-CSF, IFN-λ, and MIP1α, however, these values did not reach statistical significance.

Conclusions: Sputum IL-1β and SPLUNC1 levels are markers of PEx in all CF participants. SPLUNC1 is predictive of PEx at 60 days, whereas IL-6 is not. IL-6 is differentially increased in men at baseline and further during PEx, suggesting IL-6 may be a sex-specific PEx marker. This highlights the importance of considering sex-based differences when interpreting inflammation marker values as a clinical resource in CF care. The wide sex-based differences in sputum cytokine levels during PEx suggest that sex-specific differences contribute to clinical sexual dimorphism that should be further investigated to define their contribution to CF lung disease, PEx frequency, and mortality in women with CF.

Acknowledgements: This work was supported by NIH R01-HL081160 and R21-AI083475 (LC), NIH T32-HL007778, NIH/NHLBI K01-HL125514-01, and Cystic Fibrosis Foundation’s Fifth Year Clinical Fellowship and Pilot and Feasibility Award (CB), American Thoracic Society Foundation Unrestricted Research Award (CB).

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