LEGIONELLA-PNEUMOPHILA INFECTION IN INTRATRACHEALLY INOCULATED T-CELL-DEPLETED OR T-CELL-NONDEPLETED A J MICE/

The inflammatory response and influence of T cell depletion on the pat hogenesis of an experimental Legionella infection were studied, A/J mi ce were infected with 10(6) CFU of Legionella pneumophila intratrachea lly, With this dose all infected animals survived the infection and ba cteria were cleared from lung, spleen, liver, and kidney within 10 to 11 days, leaving no residual changes in the affected organs. Inflammat ory cells were recruited into the lung on the second day of infection, reaching a maximum on the third day and filling out predominantly the interstitial areas. During the first 3 days after inoculation, mainly macrophages, B cells, NK cells, and large mononuclear cells of an unk nown phenotype were attracted into the lung interstitium, whereas T ly mphocytes infiltrated subsequently. During the early phase of infectio n, serum concentrations of IFN-gamma, TNF-alpha, IL-1 beta, IL-4, and IL-6 but not IL-2 increased dramatically, The cytokine secretion decre ased on the third day after infection although bacteria were still pre sent in the lung or even disseminated in different organs. Successful clearance of bacteria from the lung was not observed before recruitmen t of T cells into the lung, in mice depleted of both CD4(+) and CD8(+) T cells, control of infection was impaired and lethality of infection increased. Depletion of either subset left residual antibacterial mec hanisms, which, however, were not sufficient to clear the Legionella a s rapidly as in undepleted mice.