The IL-23/IL-17 and IL-12/IFN-γ cytokine pathways have a role in chronic autoimmunity, which is considered mainly a dysfunction of adaptive immunity. The extent to which they contribute to innate immunity is, however, unknown. We used a mouse model of acute kidney ischemia-reperfusion injury (IRI) to test the hypothesis that early production of IL-23 and IL-12 following IRI activates downstream IL-17 and IFN-γ signaling pathways and promotes kidney inflammation. Deficiency in IL-23, IL-17A, or IL-17 receptor (IL-17R) and mAb neutralization of CXCR2, the p19 subunit of IL-23, or IL-17A attenuated neutrophil infiltration in acute kidney IRI in mice. We further demonstrate that IL-17A produced by GR-1+ neutrophils was critical for kidney IRI in mice. Activation of the IL-12/IFN-γ pathway and NKT cells by administering α-galactosylceramide–primed bone marrow–derived DCs increased IFN-γ production following moderate IRI in WT mice but did not exacerbate injury or enhance IFN-γ production in either Il17a–/– or Il17r–/– mice, which suggested that IL-17 signaling was proximal to IFN-γ signaling. This was confirmed by the finding that IFN-γ administration reversed the protection seen in Il17a–/– mice subjected to IRI, whereas IL-17A failed to reverse protection in Ifng–/– mice. These results demonstrate that the innate immune component of kidney IRI requires dual activation of the IL-12/IFN-γ and IL-23/IL-17 signaling pathways and that neutrophil production of IL-17A is upstream of IL-12/IFN-γ. These mechanisms might contribute to reperfusion injury in other organs.
Li Li, Liping Huang, Amy L. Vergis, Hong Ye, Amandeep Bajwa, Vivek Narayan, Robert M. Strieter, Diane L. Rosin, Mark D. Okusa
Submitter: Li Li | email@example.com
Authors: Mark D. Okusa, M.D.
University of Virginia Charlottesville, VA
Published March 24, 2010
Despite the importance of Th17 cells, several studies provide evidence that they are not the only source of IL-17A; iNKT cells NK cells and γδ T cells also produce IL-17A in inflammatory states. We provide three lines of evidence that support our conclusion that neutrophils produce IL-17A: 1) cytokine capture technique, 2) intracellular labeling showing the production of IL-17A is mainly from Gr-1 (Ly6G)+ neutrophils (Figure 5A) but not CD4, CD8 or NK1.1+ NK/NKT cells (Figure S2) and 3) direct functional studies demonstrating IL-17A producing neutrophils contribute importantly in the pathogenesis of kidney IRI, as shown by adoptive transfer of PMNs from WT, WT + treatment with anti-IL-17A mAb, and IL-17A KO mice to IL-17A KO mice at the onset of kidney IRI. The results showed significant functional protection from kidney IRI when IL-17A KO PMNs were transferred to WT IRI mice as opposed to WT PMNs transferred to WT mice. When WT PMNs were transferred to WT mice, anti-IL-17A mAb reversed the injury (Figure 5B). Therefore we believe that these complementary in vitro and in vivo studies provide compelling evidence that neutrophils are a dominant source of IL-17A and contribute importantly to kidney IRI.
We cannot exclude a potential role for γC receptor dependent cell populations in our model.
Submitter: Jay K. Kolls | firstname.lastname@example.org
LSU Health Sciences Center, New Orleans
Published February 26, 2010
Regarding the paper by Li and colleagues, there are issues with conclusions that all the IL-17 is coming from non T-cell sources and only from neutrophils. The authors rely on a cytokine capture technique as opposed to intracellular cytokine staining. As neutrophils express abundant IL-17RA and can bind free IL-17 (1), the addition of a bi-specific antibody that may have a higher affinity for IL-17 could displace bound IL-17 from IL-17RA on neutrophils as the ligand affinity of this receptor is known to be weak (2). It would seem another corroborating line of evidence such as the demonstration of transcripts for IL-17A from highly purified neutrophils would be required to justify the conclusions. Additionally the authors used RAG2-/- mice which still have IL-17 producing NK and lymphoid tissue inducer cells which are not present in RAG 2-/-, γC double knockout mice (3). In models of airway infection, where IL-23 and IL-6 are induced, there is no IL-17A or IL-22 detectable in RAG2-/-, γC double knockout mice (4) whereas RAG2-/- mice still have detectable IL-17 and IL-22 responses. Can the authors exclude a role for γC receptor dependent cell populations in their model?