Test of vaccine against Mycoplasma hyosynoviae; induction of specific B-cell memory

Mycoplasma hyosynoviae (Mhs) causes arthritis in swine. As an effective immunoprophylaxis against the disease is not available we attempt to develop one. Twenty-six Mhs-free cross-bred pigs (3 litters) from an infected herd were isolated from 3½ weeks of age. A vaccine containing formalin-inactivated Mhs (strain M60, 300μg/dose) with EMULSIGEN-BCL® (MVP Laboratories) as adjuvant was administered to 13 pigs at 7 and 10 weeks of age. Thirteen placebo pigs received adjuvant in saline. Intra-nasal challenge infection with Mhs was given 3 weeks after boost. Three pigs in the placebo group and one in the vaccine group developed lameness after inoculation (p.i.). At autopsy, 14-21 days p.i., eight vaccinated and 10 placebo pigs had pathological changes in joints. Changes were mostly mild. Before inoculation, a significantly higher level of antigen-specific IFNγ production was measured in the vaccinated group compared to the placebo group in a whole-blood assay. On day 6 p.i. the placebo group had a significantly higher IFNγ level when compared to the vaccinated group. Compared to placebo pigs, all vaccinated pigs had a more potent response in Mhs specific IgG in serum after challenge, with a more rapid onset and higher levels reached before autopsy. The latter results show that the vaccinated pigs have been primed to mount a more rapid specific antibody response after infection. In order to be able to conclude anything on the protective effect of the vaccine against clinical arthritis larger experimental groups are needed.
Keyword: Swine, vaccine, Mycoplasma hyosynoviae, EMULSIGEN, immunology