37) (Fig. 3c). To ensure that the decreased adhesion and invasion rate was a consequence of the fact that the Lcl antibodies covered Lcl and was not due to possible side effects of the antibodies, experiments were repeated with XlnC antibodies buy INK 128 of the same isotype as a control. The results obtained with the latter antibodies showed no difference in the adhesion and invasion of host cells compared with nontreated WT cells (Fig. 3d). To further exclude that masking

other adhesion factors caused by steric hindrance of bound antibodies might be the basis of the abovementioned results, Lcl-adhesion assays were performed with immobilized recombinant Lcl protein. Adhesion of the A549, macrophage-like cells and A. castellanii to the immobilized Lcl protein was influenced by preincubation of the protein film with Lcl-specific antibodies. The use of different antibody concentrations GW-572016 molecular weight demonstrated that the adhesion was specifically hindered by Lcl-specific antibodies, in an antibody concentration-dependent manner. The A549 cells showed an adhesion of 21% (P<0.001), 80% and 95% using 20, 2 and 0.2 μg Lcl-specific antibodies, respectively (Fig. 4a). The influence on the macrophage-like cell line was less pronounced, with a decrease of only

25% (P=0.06) using 20 μg of Lcl-specific antibodies (Fig. 4b). In contrast, no effect of antibody treatment was seen for the adhesion of A. castellanii to the immobilized film of Lcl, as similar results were obtained for the negative control (coated BSA) (Fig. 4c). In conclusion, the results of these incubation assays with Lcl-specific antibodies suggest that Lcl plays a role in the adhesion process of L. pneumophila. Coimmunoprecipitation experiments were performed to investigate the presence of possible partners on the host cells that interact with Lcl. The eukaryotic C1qR was suggested

to be a possible interaction partner, because it is involved in the phagocytosis pentoxifylline of microorganisms. This receptor interacts, for example, with the complement factor C1q and lung surfactant A through binding of the collagen-like region of these proteins, resulting in phagocytosis (Hoppe & Reid, 1994; Grubor et al., 2006). Moreover, the C1qR is present on both cell lines that were shown to interact with Lcl. Coimmunoprecipitation experiments using anti-C1qR antibodies and Lcl antibodies indicated an interaction between the Lcl protein of L. pneumophila Philadelphia and the C1qR of the A549 and the U937 cell line (Fig. 5). The previously described adhesion–infection assays were repeated with lung epithelial cells A549 and macrophage cell line U937 using the IPTG-inducible WT/pMMBNlcl, with 19 repeat units, and the WT/pMMBNlcl(14) strain, with 14 repeat units. The WT/pMMBNlcl(14) strain adhered to and invaded the lung epithelial cells significantly better (P=0.02) than WT/pMMBNlcl after 60 min.