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.

Bacterial pneumonia remains an important cause of morbidity and mortality worldwide, especially in immune-compromised patients. Cytokines and chemokines are critical molecules expressed in response to invading pathogens and are necessary for normal lung bacterial host defenses. Here we show that interleukin (IL)-17, a novel cytokine produced largely by CD4+ T cells, is produced in a compartmentalized fashion in the lung after challenge with Klebsiella pneumoniae. Moreover, overexpression of IL-17 in the pulmonary compartment using a recombinant adenovirus encoding murine IL-17 (AdIL-17) resulted in the local induction of tumor necrosis factor-alpha, IL-1beta, macrophage inflammatory protein-2, and granulocyte colony-stimulating factor (G-CSF); augmented polymorphonuclear leukocyte recruitment; and enhanced bacterial clearance and survival after challenge with K. pneumoniae. However, simultaneous treatment with AdIL-17 provided no survival benefit after intranasal K. pneumoniae challenge. These data show that IL-17 may have a role in priming for enhanced chemokine and G-CSF production in the context of lung infection and that optimally timed gene therapy with IL-17 may augment host defense against bacterial pneumonia.

Certain cytokines that are produced in liver may act as growth factors to facilitate wound healing and, hence, may influence liver regeneration. However, this hypothesis has not been directly tested. To determine whether the cytokine response evoked by partial hepatectomy (PH) modulates the process of liver regeneration, adult male rats were injected intraperitoneally with either goat polyclonal antibodies to rat tumor necrosis factor (TNF; 15 micrograms/g body wt) or an equal amount of goat anti-rat immunoglobulin G 1 h before PH. Animals were killed at 12, 24, 48, or 72 h post-PH, 1 h after injection with [3H]thymidine. Serum TNF levels were measured with the L929 cytotoxicity assay, titers of antibody to TNF were determined by enzyme-linked immunoabsorbent assay, and interleukin-6 (IL-6) concentrations were measured by B9 cell bioassay. Liver regeneration was assessed by [3H]thymidine incorporation into hepatic DNA and by immunohistochemical evidence of proliferating cell nuclear antigen (PCNA) expression. Antibodies to TNF were detected in treated rats but not in controls. Titers were highest at 12 h and progressively fell. Although TNF was never detected in serum, treatment with anti-TNF pre-PH significantly inhibited increases in serum IL-6 concentration post-PH. Anti-TNF pretreatment also inhibited [3H]thymidine incorporation into DNA, as well as expression of PCNA by both hepatocytes and liver nonparenchymal cells. These data indicate that TNF positively modulates liver regeneration after PH.

After liver injury, remaining hepatocytes proliferate to regenerate the liver. Although the precise mechanisms that initiate and localize regeneration are unknown, local induction of c-jun is a critical, early step in the response. Treatment of rats with antibodies to tumor necrosis factor-alpha (TNF-alpha), a mediator of liver injury, inhibits regenerative induction of jun nuclear kinase activity and nuclear c-jun expression and alters the DNA binding activity of the c-jun transcription factor, AP-1, in liver. Pretreatment with anti-TNF antibodies does not affect pulmonary or renal c-jun expression or AP-1 binding activity post-partial hepatectomy. In primary hepatocyte cultures, TNF-alpha directly promotes the proliferative actions of mitogens, supporting in vivo evidence that it sensitizes hepatocytes to mitogens. Thus local release of TNF may act in a paracrine fashion to initiate regeneration in the injured liver by promoting induction of critical growth-related genes, such as c-jun.