Early production of IL-17 protects against acute pulmonary<i>Pseudomonas aeruginosa</i>infection in mice

Interleukin-17 (IL-17) is involved in protection against extracellular bacteria. However, IL-17 is likely to be deleterious to a host with chronic pulmonary Pseudomonas aeruginosa infection. The role of IL-17 during acute pulmonary P. aeruginosa infection remains unknown. Here, we evaluated the role that IL-17 plays in acute pulmonary P. aeruginosa infection and the source of the interleukin. The production of IL-17 increased rapidly after acute pulmonary P. aeruginosa infection in mice. We subsequently examined the role of IL-17 in acute infection and found 100 times more bacteria in the bronchoalveolar lavage fluid of mice treated with an IL-17-neutralizing antibody compared with the IgG(2a) -treated mice after 16 h of infection. The main infiltrating cells in the anti-IL-17-treated mice were lymphocytes rather than neutrophils. Consistently, more tissue damage and pathological changes in the lung were observed in the anti-IL-17-treated mice. We also found that Th17 cells are one of the sources of IL-17. We conclude that the early production of IL-17 plays a protective role during acute pulmonary P. aeruginosa infection in mice and that Th17 cells are one of the sources of IL-17 during acute pulmonary P. aeruginosa infection. Altogether, IL-17 and Th17 cells contribute to the pathogenesis of acute pulmonary P. aeruginosa infection in vivo.