All treatments were carried out for 18 h in a 5% CO2 atmosphere. Determination of macrophage viability Following treatments with either the recombinant SspA or bacterial cells, cell viability was evaluated with an MTT (3-[4,5-diethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) test performed according to the manufacturer’s protocol (Roche Diagnostics, Mannheim, Germany). Determination of selleck screening library cytokine secretion Commercial enzyme-linked immunosorbent assay (ELISA) kits (R&D Systems, Minneapolis, MN, USA) were used to quantify IL-1β, IL-6, TNF-α, CCL5, and CXCL8 concentrations in the cell-free culture supernatants according to the manufacturer’s protocols. The
absorbance at 450 nm was read using a microplate reader with the wavelength correction set at 550 nm. The rated sensitivities of the commercial ELISA kits were 3.9 pg/ml for IL-1β, 9.3 pg/ml for IL-6, 15.6 Talazoparib clinical trial pg/ml for TNF-α and CCL5, and 31.2 pg/ml for CXCL8. Determination of cytokine degradation Degradation of IL-6, CXCL8, and CCL5 by the recombinant
SspA was assessed by ELISA. Briefly, recombinant cytokines (300 pg/ml of IL-6, selleck products 250 pg/ml of CXCL8, or 500 pg/ml of CCL5,) were incubated with the recombinant SspA at concentrations ranging from 0.26 to 16.5 μg/ml for 4 h. Following incubation, residual cytokines were quantified by ELISA as described above. Effect of kinase inhibitors on cytokine secretion Specific kinase inhibitors (Calbiochem, Mississauga, ON, Canada) used at the optimal concentration recommended by the manufacturer (0.0625 μM) were added to macrophages Chlormezanone 2 h prior to being treated with the recombinant SspA (0.33 μg/ml) for 18 h. The inhibitors SB203580 [p38 mitogen-activated kinase (p38MAPK) inhibitor], UO126 [mitogen-activated extracellular kinase 1, 2 (MEK 1, 2) inhibitor] and JNK inhibitor II [c-JUN N-terminal kinase (JNK) inhibitor], were evaluated for their effect on IL-6, CXCL8, and CCL5 secretion by macrophages.
Statistical analysis All treatments and cytokine determination were performed in triplicate and the means ± standard derivations were calculated. Differences were analyzed for statistical significance using the Student’s t-test and were considered significant at P < 0.01. Results Prior to determine the capacity of the recombinant SspA of S. suis to induce an inflammatory response in PMA-differentiated U937 macrophages, its effect on cell viability was evaluated. The MTT test revealed that macrophage viability was not significantly reduced (less than 20%) by a treatment with the recombinant SspA at a concentration of up to 33 μg/ml. As reported in Figure 1A-C, a significant dose-dependent secretion of all three pro-inflammatory cytokines IL-1β, IL-6 and TNF-α was observed following stimulation of macrophages with the recombinant SspA. More specifically, treatment of macrophages with SspA at 0.33 μg/ml resulted in a 2-fold, 55-fold and 7-fold increase of IL-1β, IL-6 and TNF-α levels, respectively.