HpARI Protein Secreted by a Helminth Parasite Suppresses Interleukin-33.

Infection by helminth parasites is associated with amelioration of allergic reactivity, but mechanistic insights into this association are lacking. Products secreted by the mouse parasite Heligmosomoides polygyrus suppress type 2 (allergic) immune responses through interference in the interleukin-33 (IL-33) pathway. Here, we identified H. polygyrus Alarmin Release Inhibitor (HpARI), an IL-33-suppressive 26-kDa protein, containing three predicted complement control protein (CCP) modules. In vivo, recombinant HpARI abrogated IL-33, group 2 innate lymphoid cell (ILC2) and eosinophilic responses to Alternaria allergen administration, and diminished eosinophilic responses to Nippostrongylus brasiliensis, increasing parasite burden. HpARI bound directly to both mouse and human IL-33 (in the cytokine's activated state) and also to nuclear DNA via its N-terminal CCP module pair (CCP1/2), tethering active IL-33 within necrotic cells, preventing its release, and forestalling initiation of type 2 allergic responses. Thus, HpARI employs a novel molecular strategy to suppress type 2 immunity in both infection and allergy.

Innate Lymphoid Cells Are the Predominant Source of IL-17A during the Early Pathogenesis of Acute Respiratory Distress Syndrome.

RATIONALE: IL-17A is purported to help drive early pathogenesis in acute respiratory distress syndrome (ARDS) by enhancing neutrophil recruitment. Although IL-17A is the archetypal cytokine of T-helper 17 cells, it is produced by a number of lymphocytes, the source during ARDS being unknown. OBJECTIVES: To identify the cellular source and the role of IL-17A in the early phase of lung injury. METHODS: Lung injury was induced in wild-type (C57BL/6) and IL-17 knockout (KO) mice with aerosolized LPS (100 µg) or Pseudomonas aeruginosa infection. Detailed phenotyping of the cells expressing RORγt, the transcriptional regulator of IL-17 production, in the mouse lung at 24 hours was performed by flow cytometry. MEASUREMENTS AND MAIN RESULTS: A 100-fold reduction in neutrophil infiltration was observed in the lungs of the IL-17A KO compared with wild-type mice. The majority of RORγt(+) cells in the mouse lung were the recently identified group 3 innate lymphoid cells (ILC3s). Detailed characterization revealed these pulmonary ILC3s (pILC3s) to be discrete from those described in the gut. The critical role of these cells was verified by inducing injury in recombinase-activating gene 2 KO mice, which lack T cells but retain innate lymphoid cells. No amelioration of pathology was observed in the recombinase-activating gene 2 KO mice. CONCLUSIONS: IL-17 is rapidly produced during lung injury and significantly contributes to early immunopathogenesis. This is orchestrated largely by a distinct population of pILC3s. Modulation of the activity of pILC3s may potentiate early control of the inflammatory dysregulation seen in ARDS, opening up new therapeutic targets.

Regulation of Foxp3+ inducible regulatory T cell stability by SOCS2.

Suppressor of cytokine signaling (SOCS) proteins are key regulators of CD4(+) T cell differentiation, and in particular, we have recently shown that SOCS2 inhibits the development of Th2 cells and allergic immune responses. Interestingly, transcriptome analyses have identified SOCS2 as being preferentially expressed in both natural regulatory T cells (Tregs) and inducible Tregs (iTregs); however, the role of SOCS2 in Foxp3(+) Treg function or development has not been fully elucidated. In this study, we show that despite having no effect on natural Treg development or function, SOCS2 is highly expressed in iTregs and required for the stable expression of Foxp3 in iTregs in vitro and in vivo. Indeed, SOCS2-deficient CD4(+) T cells upregulated Foxp3 following in vitro TGF-ß stimulation, but failed to maintain stable expression of Foxp3. Moreover, in vivo generation of iTregs following OVA feeding was impaired in the absence of SOCS2 and could be rescued in the presence of IL-4 neutralizing Ab. Following IL-4 stimulation, SOCS2-deficient Foxp3(+) iTregs secreted elevated IFN-γ and IL-13 levels and displayed enhanced STAT6 phosphorylation. Therefore, we propose that SOCS2 regulates iTreg stability by downregulating IL-4 signaling. Moreover, SOCS2 is essential to maintain the anti-inflammatory phenotype of iTregs by preventing the secretion of proinflammatory cytokines. Collectively, these results suggest that SOCS2 may prevent IL-4-induced Foxp3(+) iTreg instability. Foxp3(+) iTregs are key regulators of immune responses at mucosal surfaces; therefore, this dual role of SOCS2 in both Th2 and Foxp3(+) iTregs reinforces SOCS2 as a potential therapeutic target for Th2-biased diseases.

Secretory Leucoprotease Inhibitor (SLPI) Promotes Survival during Acute Pseudomonas aeruginosa Infection by Suppression of Inflammation Rather Than Microbial Killing.

Secretory leucoprotease inhibitor (SLPI) has multifaceted functions, including inhibition of protease activity, antimicrobial functions, and anti-inflammatory properties. In this study, we show that SLPI plays a role in controlling pulmonary Pseudomonas aeruginosa infection. Mice lacking SLPI were highly susceptible to P. aeruginosa infection, however there was no difference in bacterial burden. Utilising a model of P. aeruginosa LPS-induced lung inflammation, human recombinant SLPI (hrSLPI) administered intraperitoneally suppressed the recruitment of inflammatory cells in the bronchoalveolar lavage fluid (BALF) and resulted in reduced BALF and serum levels of inflammatory cytokines and chemokines. This anti-inflammatory effect of hrSLPI was similarly demonstrated in a systemic inflammation model induced by intraperitoneal injection of LPS from various bacteria or lipoteichoic acid, highlighting the broad anti-inflammatory properties of hrSLPI. Moreover, in bone-marrow-derived macrophages, hrSLPI reduced LPS-induced phosphorylation of p-IkB-α, p-IKK-α/ß, p-P38, demonstrating that the anti-inflammatory effect of hrSLPI was due to the inhibition of the NFκB and MAPK pathways. In conclusion, administration of hrSLPI attenuates excessive inflammatory responses and is therefore, a promising strategy to target inflammatory diseases such as acute respiratory distress syndrome or sepsis and could potentially be used to augment antibiotic treatment.