Identification of the immunogenic outer membrane protein A antigen of Haemophilus parasuis by a proteomics approach and passive immunization with monoclonal antibodies in mice.

Monoclonal antibodies (MAbs) against Haemophilus parasuis were generated by fusing spleen cells from BALB/c mice immunized with whole bacterial cells with SP2/0 murine myeloma cells. Desirable hybridomas were screened by enzyme-linked immunosorbent assay (ELISA). Neutralizing MAb 1D8 was selected in protection assays. ELISA results demonstrated that 1D8 can react with all 15 serotypes of H. parasuis and field isolate H. parasuis HLJ-018. Passive immunization studies showed that mice inoculated intraperitoneally with 1D8 had significantly reduced prevalence of H. parasuis colonization in the blood, lung, spleen, and liver and had prolonged survival time compared to that of the control group. Furthermore, the passive transfer experiment indicated that MAb 1D8 can protect mice from both homologous and heterologous challenges with H. parasuis. Using two-dimensional gel electrophoresis (2-DE), the immunoreactive protein target for MAb 1D8 was identified. The data presented confirm the protective role of MAb 1D8 and identify OmpA as the target of the protective monoclonal antibody. The data suggest that OmpA is a promising candidate for a subunit vaccine against H. parasuis.