Requirement of Interleukin 17 Receptor Signaling for Lung Cxc Chemokine and Granulocyte Colony-Stimulating Factor Expression, Neutrophil Recruitment, and Host Defense

TLDR

Bacterial pneumonia is a growing complication of HIV infection, correlating inversely with CD4⁺ lymphocyte counts, and IL‑17, produced by CD4⁺ T cells, drives granulopoiesis through G‑CSF and induces CXC chemokines. The study hypothesized that IL‑17 receptor (IL‑17R) signaling is essential for G‑CSF and CXC chemokine production and for lung host defenses. To test this, a Klebsiella pneumoniae lung infection model was used in mice lacking IL‑17R or overexpressing a soluble IL‑17R. IL‑17R‑deficient mice showed 100 % mortality, delayed neutrophil recruitment, increased bacterial dissemination, and markedly reduced lung G‑CSF and MIP‑2 production, proving that IL‑17R signaling is critical for neutrophil‑mediated clearance of K.

Abstract

Bacterial pneumonia is an increasing complication of HIV infection and inversely correlates with the CD4(+) lymphocyte count. Interleukin (IL)-17 is a cytokine produced principally by CD4(+) T cells, which induces granulopoiesis via granulocyte colony-stimulating factor (G-CSF) production and induces CXC chemokines. We hypothesized that IL-17 receptor (IL-17R) signaling is critical for G-CSF and CXC chemokine production and lung host defenses. To test this, we used a model of Klebsiella pneumoniae lung infection in mice genetically deficient in IL-17R or in mice overexpressing a soluble IL-17R. IL-17R-deficient mice were exquisitely sensitive to intranasal K. pneumoniae with 100% mortality after 48 h compared with only 40% mortality in controls. IL-17R knockout (KO) mice displayed a significant delay in neutrophil recruitment into the alveolar space, and had greater dissemination of K. pneumoniae compared with control mice. This defect was associated with a significant reduction in steady-state levels of G-CSF and macrophage inflammatory protein (MIP)-2 mRNA and protein in the lung in response to the K. pneumoniae challenge in IL-17R KO mice. Thus, IL-17R signaling is critical for optimal production of G-CSF and MIP-2 and local control of pulmonary K. pneumoniae infection. These data support impaired IL-17R signaling as a potential mechanism by which deficiency of CD4 lymphocytes predisposes to bacterial pneumonia.