LEGIONELLA-PNEUMOPHILA REPLICATES WITHIN RAT ALVEOLAR EPITHELIAL-CELLS

Legionella pneumophila replicates in the distal pulmonary airspace, ca using legionnaires' pneumonia. Legionella organisms replicate within a lveolar macrophages and recruited blood monocytes; however, when these cells are activated, they become potent inhibitors of L. pneumophila proliferation. L. pneumophila may replicate in other cells and thereby avoid the host defenses of macrophages. Experiments demonstrated that L. pneumophila replicate within primary cultures of rat pulmonary alv eolar epithelial cells. Double-label immunofluorescent and electron mi croscopy demonstrated L. pneumophila within epithelial cells. Replicat ion of L. pneumophila required similar numbers of alveolar epithelial cells or alveolar macrophages, required viable epithelial cells, and t ook place intracellularly. While replication of L. pneumophila occurre d in both serum-free and serum-containing media, it was enhanced in th e presence of serum. Pulmonary alveolar epithelial cells may represent an alternative site for replication of Legionella species in the term inal airspace and thus clarify some previously unexplained aspects of the pathogenesis of legionnaires' disease.