Study of the Immune Response Induced by an Attenuated Strain of Corynebacterium pseudotuberculosis in Sheep Reared Under Extensive System

Caseous Lymphadenitis (CL) is an infectious chronic disease that affects sheep and goats, worldwide distribution, caused by Corynebacterium pseudotuberculosis which leads to formation of granulomas in superficial lymph nodes and some internal organs. A naturally attenuated strain of C. pseudotuberculosis, called T1was recently isolated, showing considerable promise as likely immunogen in initial tests in mice and goats. To test this strain in sheep, twenty animals were divided into five experimental groups were inoculated with C. pseudotuberculosis T1 line into two separate doses, 2 x 105 and 2 x 107 CFU, and two groups received a booster after two months. The control group was inoculated only with saline. The animals were challenged with a wild strain of C. pseudotuberculosis, and then necropsied. An ELISA for identification of specific IgG, and IFN-γ dosage for evaluating the cellular response was used. The animals immunized with a dose 2 x 107 CFU had increased antibody production than the other groups before challenge, and this difference was not statistically significant. The IFN-γ in all groups were low before challenge with a virulent strain, but it was statistically higher after challenge in the groups inoculated with 2 x 105 CFU. The animals inoculated with the attenuated bacteria present number and injury pattern similar to those of the control group animals. The attenuated strain of C. pseudotuberculosis T1 has not shown a satisfactory induce immunoprotection in these animals against a challenge with a wild strain of C. pseudotuberculosis in sheep when tested in the field.