Louis, MO). Bacterial BB-94 Necrostatin-1 ic50 strains L. pneumophila serogroup 1 strain AA100jm [39] is a spontaneous streptomycin-resistant mutant of strain 130b, which is virulent in guinea pigs, macrophages, and amoebae. The avirulent

dotO mutant was constructed by random transposon mutagenesis, as described previously [39]. This mutation results in severe defects in intracellular growth and evasion of the endocytic pathway [40]. The Corby flaA mutant derived from the wild-type Corby is defective in flagellin [41]. L. pneumophila strains were grown at 35°C in a humidified incubator on either buffered charcoal-yeast extract-agar medium supplemented with α-ketoglutarate (BCYE-α) or in buffered yeast extract broth supplemented with α-ketoglutarate (BYE-α). The flaA mutant was grown in an environment similar to those used for other VX-680 mw strains, but in the presence of 20 μg/ml kanamycin. Heat-killed bacteria were prepared by heating the bacterial suspension at 56°C for 30 min or at 100°C for 1 h. Bacterial inactivation was achieved by treatment with paraformaldehyde (4%, 15 min followed by three washes in phosphate-buffered saline; PBS). Both types of treated suspensions were confirmed to contain no viable bacteria by plating them on BCYE-α agar. Cell culture Human T cells (Jurkat) were

maintained in RPMI 1640 medium containing 10% fetal bovine serum (FBS), 100 U/ml penicillin G, and 100 μg/ml streptomycin. Human peripheral blood mononuclear cells (PBMC) were Florfenicol isolated from peripheral blood of healthy donors using Ficoll-Hypaque gradients. PBMC were then further purified using positive selection with immunomagnetic beads specific for CD4 (Miltenyi Biotec, Auburn,

CA). On the day of the experiment, cells were refed with fresh antibiotic-free medium and cocultured with L. pneumophila for the time intervals indicated below. Infection of T cells and intracellular growth kinetics experiments Jurkat or CD4+ T cells seeded in plates were inoculated with either AA100jm or dotO mutant and either Corby or flaA mutant at an MOI of 100. In some experiments, heat-killed or paraformaldehyde-fixed bacteria were inoculated in the same manner. At 2 h after infection, cells were centrifuged and the supernatant was discarded. Cells were washed three times with PBS and resuspended in fresh RPMI 1640 medium containing 100 μg/ml gentamycin for 2 h. The cells were washed three times again with PBS and were further incubated with fresh medium. The infected cells and supernatant in each well were harvested at the indicated time intervals by washing the wells three times with sterilized distilled water. These bacterial suspensions were diluted in sterilized water and plated in known volume onto BCYE-α agar. The numbers of CFU in infected cells were counted at the indicated time points after infection.