Abstract
Interleukin (IL-) 36 cytokines (previously designated as novel IL-1 family member cytokines; IL-1F5– IL-1F10) constitute a novel cluster of cytokines structurally and functionally similar to members of the IL-1 cytokine cluster. The effects of IL-36 cytokines in inflammatory lung disorders remains poorly understood. The current study sought to investigate the effects of IL-36α (IL-1F6) and test the hypothesis that IL-36α acts as a pro-inflammatory cytokine in the lung in vivo. Intratracheal instillation of recombinant mouse IL-36α induced neutrophil influx in the lungs of wild-type C57BL/6 mice and IL-1αβ−/− mice in vivo. IL-36α induced neutrophil influx was also associated with increased mRNA expression of neutrophil-specific chemokines CXCL1 and CXCL2 in the lungs of C57BL/6 and IL-1αβ−/− mice in vivo. In addition, intratracheal instillation of IL-36α enhanced mRNA expression of its receptor IL-36R in the lungs of C57BL/6 as well as IL-1αβ−/− mice in vivo. Furthermore, in vitro incubation of CD11c+ cells with IL-36α resulted in the generation of neutrophil-specific chemokines CXCL1, CXCL2 as well as TNFα. IL-36α increased the expression of the co-stimulatory molecule CD40 and enhanced the ability of CD11c+ cells to induce CD4+ T cell proliferation in vitro. Furthermore, stimulation with IL-36α activated NF-κB in a mouse macrophage cell line. These results demonstrate that IL-36α acts as a pro-inflammatory cytokine in the lung without the contribution of IL-1α and IL-1β. The current study describes the pro-inflammatory effects of IL-36α in the lung, demonstrates the functional redundancy of IL-36α with other agonist cytokines in the IL-1 and IL-36 cytokine cluster, and suggests that therapeutic targeting of IL-36 cytokines could be beneficial in inflammatory lung diseases.
Highlights
The Interleukin 1 (IL-1) cytokine cluster consists of a network of agonist, antagonist and receptor molecules that are expressed in a variety of immune and structural cells [1]
Flow cytometric evaluation of Bronchoalveolar lavage (BAL) cells revealed that majority of cells recovered from BAL fluid of IL-36a instilled mice were CD11c2CD11b+Ly6G+ neutrophils, while a majority of cells recovered from the BAL fluid of PBS instilled mice were CD11c+CD11b2Ly6G2 cells, reflective of macrophages (Fig. 1G)
Macrophages were the main cell types present in the BAL fluid of PBS instilled C3H/HeJ mice. These results strongly suggest that the neutrophil influx observed in the lungs of mice is due to the agonist activity of IL-36a and not due to contaminants in the protein preparation
Summary
The Interleukin 1 (IL-1) cytokine cluster consists of a network of agonist, antagonist and receptor molecules that are expressed in a variety of immune and structural cells [1]. Increased levels of IL-1 protein or mRNA, reflective of increased IL-1 cytokine activity, has consistently been observed in tissues from human patients with inflammatory lung disorders such as asthma [4,5,6,7], acute lung injury [8,9,10] and pulmonary fibrosis [11]. Studies from animal models have demonstrated that IL1 cytokines such as IL-1a and IL-1b play critical roles in the pathogenesis of asthma [12,13,14], chronic obstructive pulmonary disease [15,16], acute lung injury [17] and pulmonary fibrosis [18,19,20]. While IL-1 induced the recruitment of neutrophils and pulmonary inflammation during the early stages of influenza infection in mice [24], it was critical in conferring protective immunity and enhancing survival of mice during the later stages of the disease [24,25,26]
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