Assessment of immunological response to digital dermatitis pathogen derived antigens following induction, recovery, and reinduction

Authors: COATNEY, JOHN - Iowa State University; GORDEN, PATRICK - Iowa State University; SHEARER, JAN - Iowa State University; KRULL, ADAM - Iowa State University; Humphrey, Samuel; Olsen, Steven; PLUMMER, PAUL - University Of Tennessee; Wilson-Welder, Jennifer

Submitted to: Frontiers in Veterinary Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/4/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: Digital dermatitis is a polymicrobial disease causing severe lameness in cattle and other hooved animals. To determine if prior exposure to the disease would create any protection from severe lesion formation on subsequent exposure, a group of Holstien cattle were experimentally inoculated, allowed to develop lesions, the digital dermatitis lesions treated and then after a brief rest, inoculated a second time to induce lesions. Three of the eight previously infected calves were protected or did not develop severe lesions on re-infection. Measurements of humoral or antibody and cell-based immunological responses did not identify differences between protected and non-protected calves other than a general decrease in responsive cells in multiple exposure animals. More study is needed to determine mechanism of protection in repeated exposure and what might be happening at local vs. systemic levels.

Technical Abstract: The ability to reliably induce bovine digital dermatitis (DD) in naive calves provides a unique opportunity to evaluate the immune response of the calves to infection with DD associated organisms when disease is induced, then healed, and subsequently re-induced. Recently weaned dairy calves with a known history of DD naivete were used to assess post-lesion immune responses with minimal immunologic noise and background. Calves infected in a previous induction trial were allowed to heal completely and were then re-induced alongside naïve calves that had served as controls in the previous trial. Previously induced calves were compared with previously naïve calves to assess immune protection due to prior exposure. Serum samples collected prior to induction, at the conclusion of the initial induction, and at the conclusion of the second induction. All feet were photographed and scored by a single blinded observer using a previously described induced lesion scoring system. Humoral and cell-mediated immunity was assessed via serum antibody titer and lymphocyte proliferation analysis. Three of the eight calves that had been infected in the initial induction trial failed to produce lesions consistent with DD in any feet. When feet are the unit of measure rather than calves, in the naïve group 15/26 developed lesions commensurate with DD, while 11/26 did not, while in the previously induced group, 10/25 developed lesions, while 15/25 feet did not. The gd T cell population was found to be in slightly increased in relative numbers in the protected group. Results indicated that digital dermatitis infection, when followed by complete resolution, appeared to provide partial protection against reinfection. Humoral immunity appeared to have no role in the protective immune response, and protected calves had a decreased cell-mediated immune response apart from gd T cells, which appear in greater numbers in the protected group. Further studies are needed to determine mechanisms behind the partial protection of previous exposure and the lack of measurable immunological protection systemically.