Introduction.

Bovine paratuberculosis is caused by infection of young calves with Mycobacterium paratuberculosis, and results in chronic granulomatous infection of the ileum. The aim of the present study was to perform a longitudinal follow up of immunological and microbiological parameters of calves experimentally infected in the first month of life.

Materials and methods.

White blood cell counts and differentiation were done on whole blood samples. PBMC were isolated from blood samples of 20 experimentally infected calves and 10 uninfected control animals. The PBMC were phenotyped by flow cytometry using a panel of 8 monoclonal antibodies. Lymphoproliferation assays, with a panel of 6 mycobacterial antigens were used for evaluating T cell function. Fecal culture was performed to aqcuire data on the mycobacterial load.

Results and conclusion.

The results obtained during the first 3 years of infection indicated that minor responses in the PBMC population of infected calves can be detected within 3 months after infection, followed by an exponentially rise 1 year post infection to reach a plateau. By the end of the third year, the indications of a decrease in cell mediated immune responses became evident. The immunophenotyping of the PBMC showed differences in the gamma-delta T cell and B-cell frequencies between the infected and the control group. Comparisons of lymphocyte stimulation and bacterial load in the infected group indicated a dose-response relationship. Definite conclusions on whether the observed immunological responses are the correlates of protective immunity awaits completion of this ongoing study.