Summary Sex hormones regulate many autoimmune and inflammatory diseases, including asthma. As adults, asthma prevalence is 2-fold greater in women compared to men. Group 2 innate lymphoid cells (ILC2) are increased in asthma, and we investigated how testosterone attenuated ILC2 function. In patients with moderate to severe asthma, we determined that women had increased circulating ILC2 numbers compared to men. In mice, ILC2 from adult females had increased IL-2-mediated ILC2 proliferation versus ILC2 from adult males and pre-pubescent females and males. Further, 5α-dihydrotestosterone, a hormone downstream of testosterone, decreased lung ILC2 numbers and IL-5 and IL-13 expression from ILC2. In vivo, testosterone attenuated Alternaria extract-induced IL-5+ and IL-13+ ILC2 numbers and lung eosinophils by intrinsically decreasing lung ILC2 numbers and cytokine expression as well as decreasing expression of IL-33 and TSLP, ILC2 stimulating cytokines. Collectively, these findings provide a foundational understanding in the sexual dimorphism in ILC2 function.

Background Respiratory syncytial virus (RSV) is a major healthcare burden with a particularly high worldwide morbidity and mortality rate among infants. Data suggest that severe RSV-associated illness is in part caused by immunopathology associated with a robust type 2 response. Objective To determine the capacity of RSV-infection to stimulate group 2 innate lymphoid cells (ILC2) and the associated mechanism in a murine model. Methods WT BALB/c, TSLPR KO, or WT mice receiving an anti-TSLP neutralizing antibody were infected with the RSV strain 01/2-20. During the first 4–6 days of infection, lungs were collected for evaluation of viral load, protein concentration, airway mucus, airway reactivity, or ILC2 numbers. Results were confirmed with two additional RSV clinical isolates, 12/11-19 and 12/12-6, with known human pathogenic potential. Results RSV induced a 3-fold increase in the number of IL-13-producing ILC2 at day 4 postinfection with a concurrent increase in total lung IL-13 levels. Both TSLP and IL-33 were increased 12 hours post-infection. TSLPR KO mice failed to mount an IL-13-producing ILC2 response to RSV infection. Additionally, neutralization of TSLP significantly attenuated the RSV-induced IL-13-producing ILC2 response. TSLPR KO mice displayed reduced lung IL-13 protein, decreased airway mucus and reactivity, attenuated weight loss, and similar viral loads as WT mice. Both 12/11-19 and 12/12-6 similarly induced IL-13-producing ILC2 via a TSLP-dependent mechanism. Conclusion These data demonstrate that multiple pathogenic strains of RSV induce IL-13-producing ILC2 proliferation and activation via a TSLP-dependent mechanism in a murine model and suggest the potential therapeutic targeting of TSLP during severe RSV infection.

ILC2s are potent mucosal effector cells that participate in type 2 inflammatory responses. Stier et al. demonstrate that IL-33 negatively regulates CXCR4, mediating the egress of ILC2 lineage cells from the bone marrow for potential hematogenous trafficking.

Rationale: Group 2 innate lymphoid cells (ILC2s) robustly produce IL-5 and IL-13, cytokines central to the asthma phenotype; however, the effect of prostaglandin (PG) I 2 on ILC2 function is unknown.Objectives: To determine the effect of PGI 2 on mouse and human ILC2 cytokine expression in vitro and the effect of endogenous PGI 2 and the PGI 2 analog cicaprost on lung ILC2s in vivo.Methods: Flow-sorted bone marrow ILC2s of wild-type (WT) and PGI 2 receptor-deficient (IP 2/2 ) mice were cultured with IL-33 and treated with the PGI 2 analog cicaprost. WT and IP 2/2 mice were challenged intranasally with Alternaria alternata extract for 4 consecutive days to induce ILC2 responses, and these were quantified. Prior to A. alternata extract, challenged WT mice were treated with cicaprost. Human flow-sorted peripheral blood ILC2s were cultured with IL-33 and IL-2 and treated with the PGI 2 analog cicaprost. Measurement and Main Results:We demonstrate that PGI 2 inhibits IL-5 and IL-13 protein expression by IL-33-stimulated ILC2s purified from mouse bone marrow in a manner that was dependent on signaling through the PGI 2 receptor IP. In a mouse model of 4 consecutive days of airway challenge with an extract of A. alternata, a fungal aeroallergen associated with severe asthma exacerbations, endogenous PGI 2 signaling significantly inhibited lung IL-5 and IL-13 protein expression, and reduced the number of lung IL-5-and IL-13-expressing ILC2s, as well as the mean fluorescence intensity of IL-5 and IL-13 staining. In addition, exogenous administration of a PGI 2 analog inhibited Alternaria extract-induced lung IL-5 and IL-13 protein expression, and reduced the number of lung IL-5-and IL-13-expressing ILC2s and the mean fluorescence intensity of IL-5 and IL-13 staining. Finally, a PGI 2 analog inhibited IL-5 and IL-13 expression by human ILC2s that were stimulated with IL-2 and IL-33.Conclusions: These results suggest that PGI 2 may be a potential therapy to reduce the ILC2 response to protease-containing aeroallergens, such as Alternaria.

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