Use of serological and mucosal immune responses to Mycoplasma hyopneumoniae antigens P97R1, P46 and P36 in the diagnosis of infection.

Currently available ELISAs used to diagnose Mycoplasma hyopneumoniae infection in pigs have high specificity but low sensitivity. To develop more sensitive assays, the kinetics of specific serum IgG and respiratory mucosal sIgA responses against three M. hyopneumoniae antigens, namely, P97R1 (an adhesin protein), P46 (a membrane protein), and P36 (a cytosolic protein), were characterised over 133 days following experimental infection. Immunoglobulin G against the three proteins remained at high concentrations from 28 to 133 days post-infection (dpi), although IgG against P97R1 was detected earlier and was more reactive than the other two antigens under assessment. Mucosal sIgA appeared earlier than serum IgG but did not persist as long; sIgA concentrations against P97R1 were the highest. Seroconversion was detected 2 weeks earlier with the P97R1-based ELISA than with a commercially available ELISA. On analysis of serum samples from five pig farms that did not use a M. hyopneumoniae vaccine, the P97R1-based IgG ELISA demonstrated a 73.6% coincidence rate with the commercial kit. Moreover, this more specific P97R1-based ELISA detected more positive samples than the commercial kit (52.8% vs. 39.2%). It was concluded that the systemic immune response to M. hyopneumoniae infection in pigs was delayed in onset but persistent whereas the mucosal response developed more rapidly but was less sustained. The P97R1 antigen was identified as a suitable serological marker for diagnosing M. hyopneumoniae infection in pigs, particularly early stage infection.