Submitted to: Infection and Immunity
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/5/1999
Publication Date: N/A
Interpretive Summary: Johne's disease is a chronic, debilitating intestinal disorder in cattle characterized by diarrhea, reduced feed intake, weight loss and death. Cattle usually become infected as young calves by ingesting feces containing the causative bacteria. However, symptoms of disease do not usually present themselves until the animals reach 3 to 5 years of age or even older. During this time the animal is infected and may be shedding the organism in its feces without showing any clinical signs of disease. In addition to reduced production by these animals through reduced milk production, they also present a potential infective threat to the rest of the herd. Johne's disease is difficult to diagnose and therefore to control. Development of accurate and sensitive diagnostic tests is dependent upon understanding the immune responses of the host animal during infection. In this study, we measured activity of immune cells upon stimulation with various cell activators in noninfected animals and in bot subclinically and clinically infected cows. Results of this study suggest that there is a difference in activity of one population of immune cells during subclinical infection. It is possible that this information will lead to a new method for detection of subclinical paratuberculosis infection.
Technical Abstract: Mycobacterium avium subsp. paratuberculosis infection of cattle results in a chronic granulomatous enteritis. Clinical disease (i.e., with cachexia, diarrhea, and high fecal bacterial counts) is preceded by a lengthy subclinical stage of disease. Immunologic mechanisms associated with progression of infected cattle from subclinical disease are unclear. In this study, a cell proliferation assay in combination with flow cytometry was used to compare peripheral blood lymphocyte responses of cattle with subclinical paratuberculosis to responses of cattle with clinical paratuberculosis. B cells from cattle with subclinical disease proliferated vigorously upon in vitro antigen stimulation with up to 12.4% of the total B cells responding. However, B cells from cattle with clinical disease did not proliferate upon antigen stimulation despite good proliferation to ConA stimulation. In addition, these animals had high percentages of peripheral blood B cells. B cells from non-infected animal did not proliferate upon Mycobacterium avium subsp. paratuberculosis antigen stimulation. Thus, it appears that B cell proliferation is a sensitive indicator of subclinical Johne's disease. Furthermore, induction of peripheral blood B cell antigen-specific unresponsiveness may be associated with progression of cattle from subclinical to clinical Johne's disease.