Paratuberculosis is a chronic granulomatous inflammation of the small intestine of cattle and other ruminants, caused by infection with Mycobacterium avium ssp. paratuberculosis(MAP). The disease can be found in ruminant herds worldwide, causing substantial economic losses at farm level due to premature culling and production losses. We have documented previously that mycobacterial heat-shock proteins (Hsp) are dominant antigens in various stages of bovine paratuberculosis. Especially the 70 kD Hsp (Hsp70) induces cell mediated responses in natural infection. Furthermore, recombinant MAP Hsp70 has been shown to be a successful subunit vaccine against bovine paratuberculosis. Surprisingly the main hallmark of vaccination induced immunity was antibody production rather than T cell immunity.

To explore the immunological mechanisms of induction of early cellular responses at the local draining lymphnodes within days after vaccination we adopted a murine model. Balb/c mice were vaccinated with Hsp70 and DDA adjuvant (Hsp70/DDA), comparable to the cattle vaccine. OVA/DDA was used as a control treatment. BrdU incorporation was measured by flowcytometry 4 and 7 days after vaccination with either vaccine. In addition lymph node cells and splenocytes were restimulated in vitro to address the functional differentiation of the immune response as measured by in vitro restimulation and antibody production.

Enhanced BrdU incorporation was observed in draining lymphnodes of mice that were immunized with Hsp70 compared to OVA treated mice 7 days after immunization. No differences in BrdU incorporation were observed in non-draining lymphnodes or at day 4 after immunization. Cellular proliferation following in vitro restimulation at 7 days after vaccination indicated equal responses against OVA and Hsp70. In addition, in vitro B cell restimulation showed an enhanced antigen specific B cells response in the draining lymph nodes only after Hsp70 vaccination at day 7, whereas B cells isolated from OVA treated mice did not produce significant amounts of antibodies in an antigen specific fashion.

Similar to the immunization outcome in cattle in the murine model there is a preferential activation of B cell activity following subcutaneous Hsp70/DDA vaccination. Therefore, the murine model presented in this study offers a convenient means to study the mechanism leading to this immuneresponse bias which is opposite to Hsp70 immune responses in natural infection and yet confers protective immunity to paratuberculosis.