Differential systemic antibody responses to Mycoplasma synoviae MSPA variants after vaccination and/ or field challenge

Mycoplasma synoviae has a major immunodominant surface protein VlhA (variable lipoprotein and haemagglutinin) which undergoes post-translational cleavage to form two separate proteins, MSPA and MSPB. Both these proteins are targets of the host immune response undergo high frequency antigenic variation and are thought to contribute to the pathogenesis of M. synoviae infection. In order to assess variation of MSPA in response to vaccination and/ or field challenge host systemic humoral responses after inoculation with M. synoviae strain 86079/7NS (7NS), vaccine strain MS-H and/or field strain 94011/v-18d (v-18d) were evaluated against eight variable regions of MSPA derived from M. synoviae type strain WVU-1853. At 21 days post-infection, chickens inoculated with 7NS had significantly higher antibody levels against MSPA B3 and B4 compared to those inoculated with the vaccine strain MS-H. Also, at 21 days post-challenge, chickens which had been inoculated with the MS-H vaccine strain prior to challenge had significantly lower antibody responses against MSPA C2 compared to those which had not been. This suggests that variants of MSPA are differentially expressed after vaccination and/ or challenge and antibodies against these variants may be strain dependent. The results of this study have implications for the differentiation of serological responses after M. synoviae vaccination and field challenge.