Immunogenicity of PtpA secreted during Mycobacterium avium ssp. paratuberculosis infection in cattle.

Aims: Mycobacterium avium subsp. paratuberculosis (MAP) is the etiological agent of Johne's disease. To survive within host macrophages, the pathogen secretes a battery of proteins to interfere with the immunological response of the host. One of these proteins is tyrosine phosphate A (PtpA), which has been identified as a secreted protein critical for survival of its close relative M. tuberculosis within infected macrophages. Methods and results: In this study, the immune response to recombinant PtpA used as an antigen was investigated in a cohort of similar to 1000 cows infected with MAP compared to negative control animals using ELISA. The sera from MAP-infected cows had significantly higher levels of antibodies against PtpA when compared to uninfected cows. Conclusions: The data presented here indicate that the antibodies produced against PtpA are sensitive enough to detect infected animals before the appearance of the disease symptoms. Significance and impact of study: The use of PtpA as an antigen can be developed as an early diagnostic test. Moreover, PtpA is a candidate antigen for detection of humoral immune responses in cows infected with MAP.