Abstract

Background: Pneumococcal pneumonia is characterized by a high recruitment of neutrophils and excessive lung damage. Several reports have shown that besides their role in acute inflammation, neutrophils may also display anti-inflammatory properties. Data obtained in our laboratory show that neutrophils produce IL-10 during pneumococcal pneumonia. However, the relevance of these IL-10- producing neutrophils in response to Streptococcus pneumoniae infection remains unknown. Objective: 1. To determine the role of IL-10–producing neutrophils during pneumococcal pneumonia. 2.To evaluate whether S. pneumoniae directly induces the IL-10 production in neutrophils. Methods: C57BL/6 wild type (WT) and IL-10-/- mice (the latter highly susceptible to S. pneumoniae infection), were intranasally transferred with WT or IL-10-/- neutrophils. 24 h later, mice were infected with 3x107 S. pneumoniae CFUs. Lung infiltration and bacterial loads were evaluated after 1 day postinfection and a 10 days survival curve was performed. Further, neutrophils isolated from mouse bone marrow cells were exposed to S. pneumoniae molecular patterns and after 24 h post treatment the amount of IL-10 secreted to culture supernatants was evaluated by ELISA. Results: The adoptive transfer of neutrophils improved IL-10-/- mice survival rate. In contrast, WT mice transferred with WT cells showed an increased clinical score and decreased survival. Furthermore, S. pneumoniae molecular patterns showed to be enough to induce high levels of IL-10 production in neutrophils. Conclusions. Our data show that neutrophils play a critical role during S. pneumoniae lung infection and suggest that IL-10 production by these cells, induced by bacteria, is crucial in disease outcome.