Granulocyte-macrophage colony-stimulating factor (GM-CSF) enhances pulmonary defenses against pneumococcal infections after splenectomy

Background: Splenectomized individuals are at risk for pneumococcal sepsis. Alveolar macrophage bactericidal function is depressed after splenectomy. Granulocyte-macrophage colony stimulating factor (GM-CSF) has pronounced effects on the number and function of macrophages, We hypothesized that GM-CSF treatment could improve alveolar macrophage bactericidal activity against pneumococci, and improve survival with pneumococcal infection. Methods: Two weeks after splenectomy or sham operation, mice were treated with GM-CSF or saline twice daily for varying times. Alveolar macrophages were obtained by bronchopulmonary lavage, and bactericidal activity was measured. Survival was assessed after pneumococcal aerosol challenge. Results: Alveolar macrophage bactericidal activity was improved with GM-CSF treatment in both eusplenic and asplenic mice (p < 0.001), GM-CSF treatment improved survival in both groups (p < 0.001). Conclusions: GM-CSF can augment alveolar macrophage function and provide protection against pneumococcal infections. It may be a useful adjuvant therapy for normal and splenectomized individuals.