Cellular and humoral immune responsiveness to inactivated Leptospira interrogans in dogs vaccinated with a tetravalent Leptospira vaccine.

Vaccination is commonly used to protect dogs against leptospirosis, however, memory immune responses induced by canine Leptospira vaccines have not been studied. In the present study, antibody and T cell mediated responses were assessed in dogs before and 2 weeks after annual revaccination with a commercial tetravalent Leptospira vaccine containing serogroups Canicola and Australis. Vaccination significantly increased average log2 IgG titers from 6.50 to 8.41 in year 1, from 5.99 to 7.32 in year 2, from 5.32 to 8.32 in year 3 and from 5.32 to 7.82 in year 4. The CXCL-10 levels, induced by in vitro stimulation of PBMC with Canicola and Australis, respectively, significantly increased from 1039.05 pg/ml and 1037.38 pg/ml before vaccination to 2547.73 pg/ml and 2730.38 pg/ml after vaccination. IFN-γ levels increased from 85.60 pg/ml and 178.13 pg/ml before vaccination to 538.62 pg/ml and 210.97 pg/ml after vaccination. The percentage of proliferating CD4+ T cells in response to respective Leptospira strains significantly increased from 1.43 % and 1.25 % before vaccination to 24.11 % and 14.64 % after vaccination. Similar responses were also found in the CD8+ T cell subset. Vaccination also significantly enhanced the percentages of central memory CD4+ T cells from 12 % to 26.97 % and 27.65 %, central memory CD8+ T cells from 3 % to 9.47 % and 7.55 %, and effector CD8+ T cells from 3 % to 7.6 % and 6.42 %, as defined by the expression of CD45RA and CD62L, following stimulation with Canicola and Australis, respectively. Lastly, enhanced expression of the activation marker CD25 on T cells after vaccination was found. Together, our results show that next to IgG responses, also T cell responses are induced in dogs upon annual revaccination with a tetravalent Leptospira vaccine, potentially contributing to protection.