Legionella pneumophila Selleck Dorsomorphin in the replicative growth phase is not proficient at infecting macrophages or preventing phagolysosome maturation (Byrne & Swanson, 1998; Hammer & Swanson, 1999). Only in the PE-phase do the bacteria acquire the capacity to evade lysosomal degradation. In the E-phase, small vesicles are typically still connected to the cell wall, but released LPS structures were also observed, whereas in the PE-phase, vesicles were profusely released (Helbig et al., 2006b). This explains our data for

inhibitory activity by OMV in the PE-phase and not in the E-phase (Fig. 1). The inhibitory effect of OMV on phagosome maturation is due to the host cell-modulating components inside the vesicles (Helbig et al., 2006a; Galka et al., 2008) and due to its LPS surface structures, respectively, most probably both. The involvement of LPS in L. pneumophila pathogenesis has been under discussion since phase-variable expression of the LPS was found to show a phase-variant mutant (Lüneberg et al., 1998). Our data show for the first time that LPS is an independent

factor for evasion of lysosomal degradation independent of whether it exhibits virulence traits (Fig. 1). LPS fractions <300 kDa obtained in the E-phase significantly delay phagolysosomal maturation 1 h after phagocytosis (P<0.001), likewise obtained in the PE-phase. The LPS of L. pneumophila serogroup 1 exhibits peculiar chemical features,

which may account for its Tofacitinib research buy importance Celecoxib as a bacterial virulence factor (Zähringer et al., 1995). We used Corby strain (MAb 3/1-positive) and its mutant TF 3/1 (MAb 3/1-negative) as the only option to explore the impact of differences in LPS hydrophobicity on the modulation of host cells, because the bacterial genomic equipment differs only in one gene expressing an enzymatically active or a nonactive O-acetyltransferase (Zou et al., 1999; Lück et al., 2001). MAb 3/1 recognizes an epitope associated with the highest degree of O-chain hydrophobicity among serotypes of L. pneumophila (Helbig et al., 1995; Knirel et al., 2001), whereas the mutant possesses, instead of 8-O-acetyl groups, free hydroxyl groups on the legionaminic acid homopolymere. Contrary to our consideration, both LPS types showed similar inhibitory effects (Figs 1 and 2). However, we have no quantitative data on hydrophobicity and its relationship between the dose and the impact on the host cell. Therefore, it cannot be ruled out that the increased hydrophobicity of MAb 3/1-positive LPS has no additional impact on the modulation of phagolysosome maturation caused by the already high degree of hydrophobicity of MAb 3/1-negative LPS.