Opsonic capacity of monoclonal antibodies anti-Vta8 and VtaA9 as determined in opsophagocytosis assay. Phagocytosis-resistant strain PC4-6P (gray bars) was incubated with monoclonal antibodies 69C6, 95F4 and 80H8, against VtaA8 and VtaA9, to allow opsonization of the bacteria. The opsonic capacity of these antibodies was then evaluated in an opsonophagocytosis assay with porcine alveolar macrophages (PAM). Opsonization with a rabbit anti-H. parasuis serum was included as a positive control. Also, two phagocytosis-susceptible strains, SW114 and F9 (black bars), were included in the assay. MO indicates non-infected macrophages (white bar). The results show the mean of the percentage of PAM with associated bacteria from triplicate wells, and the error bars are the standard deviation. For strain SW114 the error bar is too small to be seen. Significant differences were detected between the phagocytosis after PC4-6P opsonization with 69C6, 95F4 and rabbit anti-H. parasuis compared to the non-opsonized PC4-6P (Student t-test, p < 0.001). Monoclonal 80H8 demonstrated no opsonic capacity.