Host defenses against bacterial lower respiratory tract infection.

Bacterial pneumonia continues to be a significant cause of morbidity and mortality worldwide. Recent studies have shown that lung epithelia signal through pattern recognition receptors to initiate the innate immune response. Other mediators of innate immunity against bacterial pneumonia include transepithelial dendritic cells, alveolar macrophages, and innate produces of IL-17. CD4+ T cells and B cells play a key role in eliminating and preventing the development of bacterial pneumonias. B cell development and maturation can be modulated by the lung epithelia through BAFF and APRIL, furthering our current understanding of the role of epithelial cells in the immune response.