Figure 1
The capacity of Salmonella enterica to downregulate MHC expression on the surface of porcine macrophages, Salmonella invasion capacity in macrophages and the effect of opsonization of Salmonella with negative and positive pig serum on intracellular proliferation and on reactive oxygen species (ROS) production. A. The average mean PAMinf/PAMuninf ratios (± standard deviation) measured in the FL-5 channel, 0 h (grey bars) and 24 h (black bars) post inoculation (pi) with Salmonella Typhimurium strain 112910a or its isogenic deletion mutants ΔhilA and ΔssrA/B, and their respective complements ΔhilAc and ΔssrA/Bc. The values were calculated from the ratios obtained from 3 independent experiments and an asterisk refers to a significantly different average mean fluorescence ratio (p ≤ 0.05). PAMinf and PAMuninf: infected and uninfected porcine alveolar macrophages, respectively. MHC I and MHC II: expression of MHC I or MHC II molecules, respectively, in macrophages inoculated with strain 112910a; 112910aNEG: Salmonella Typhimurium strain 112910 opsonized with negative pig serum; 112910aPOS: Salmonella Typhimurium strain 112910 opsonized with pig serum containing Salmonella Typhimurium specific antibodies. B. Salmonella Typhimurium strain 112910a invasion capacity in porcine macrophages after opsonization with negative and positive pig serum. The relative invasiveness of Salmonella Typhimurium hilA deletion mutant (ΔhilA) and its complement (ΔhilAc) was used as an internal control. Salmonella invasiveness was expressed as the percentage relative to the invasion capacity of strain 112910a ± standard deviations. Each bar represents the average of three independent experiments. An asterisk (*) indicates a significantly different invasion capacity compared to strain 112910a (p ≤ 0.05). C. The average 10log CFU of Salmonella Typhimurium strain 112910a that was either not opsonized, opsonized with negative pig serum or opsonized with serum containing Salmonella specific antibodies per mL, recovered from macrophages immediately (grey bars) or 5 h (black bars) post inoculation (pi). Bars with an asterisk represent significant bacterial proliferation at 5 h post inoculation (p ≤ 0.05). D. ROS production of macrophages inoculated with Salmonella Typhimurium strain 112910a that was not opsonized or opsonized with negative or positive pig serum. The ROS production of infected macrophages was expressed relative to the ROS production of phorbol 12-myristate 13-acetate (PMA) treated macrophages (positive control). Each bar represents the average of two independent experiments conducted in triplicate. An asterisk (*) indicates a statistically significant difference in ROS production (p ≤ 0.05)