COINOCULATION WITH HARTMANNELLA-VERMIFORMIS ENHANCES REPLICATIVE LEGIONELLA-PNEUMOPHILA LUNG INFECTION IN A MURINE MODEL OF LEGIONNAIRES-DISEASE

The effect of inhaled amoebae on the pathogenesis of Legionnaires' dis ease was investigated in vivo. A/J mice, which are susceptible to repl icative Legionella pneumophila infections, were inoculated intratrache ally with L. pneamophila (10(6) bacteria per mouse) or were coinoculat ed with L. pneumophila (10(6) bacteria per mouse) and Hartmannella ver miformis (10(6) amoebae per mouse). The effect of coinoculation with H . vermiformis on bacterial clearance, histopathology, cellular recruit ment into the lung, and intrapulmonary levels of cytokines including g amma interferon and tumor necrosis factor alpha was subsequently asses sed. Coinoculation with H. vermiformis significantly enhanced intrapul monary growth of L. pneumophila in A/J mice. Histopathologic and flow cytometric analysis of lung tissue demonstrated that while A/J mice in oculated with L. pneumophila alone develop multifocal pneumonitis whic h resolves with minimal mortality, mite coinoculated with H. vermiform is develop diffuse pneumonitis which is associated with diminished int rapulmonary recruitment of lymphocytes and mononuclear phagocytic cell s and significant mortality. Furthermore, coinoculation of mice with H . vermiformis resulted in a fourfold enhancement in intrapulmonary lev els of gamma interferon and tumor necrosis factor alpha compared with mice infected with L. pneumophila alone. The effect of H. vermiformis on intrapulmonary growth of L. pneumophila in a resistant host (i.e., BALB/c mice) was subsequently evaluated. While BALB/c mice do not deve lop replicative L. pneumophila infections following inoculation with L . pneumophila alone, there was an eightfold increase in intrapulmonary L. pneumophila in BALB/c mice coinoculated with H. vermiformis. These studies, demonstrating that intrapulmonary amoebae potentiate replica tive L. pneumophila lung infection in both a susceptible and a resista nt host, have significant implications with regard to the potential ro le of protozoa in the pathogenesis of pulmonary diseases due to inhale d pathogens and in the design of strategies to prevent and/or control legionellosis.