Humoral and cellular immune responses in cattle upon Clostridium chauvoei vaccination and challenge

Abstract

Introduction: Clostridium chauvoei is the causative agent of blackleg, a severe disease in cattle. Vaccination reduces disease incidence but the immune mechanisms that underlie vaccine-induced protection remain poorly understood, particularly the role of cellular immunity. In this study we characterized the humoral and cellular immune responses induced by a polyclostridial vaccine and assessed their correlation with protection against a C. chauvoei challenge. Methods: Eleven six month old Hereford calves, seronegative for anti C. chauvoei antibodies, were randomized into vaccinated (n=8) and control (n=3) groups. Vaccinated animals received two doses of the vaccine at days 0 and 42 days. All animals were intramuscularly challenged with C. chauvoei spores (8,000 LD50) at day 69 post vaccination and monitored for clinical outcomes. Blood samples were collected at pre-vaccination and pre- and post-challenge. Humoral responses were quantified by specific in-house developed ELISA. Cytokine gene expression was measured in whole-blood (RT-qPCR for IFN g, TNF a, TGF b1, IL 4, IL 17A, IL 12B, IL 10) upon antigenic stimulation. Results: While vaccination protected cattle upon challenge and all animals survived, unvaccinated controls developed severe disease and died. Vaccination induced a strong specific antibody response although with inter-individual variationaswell as a specific cytokine profile characterized by increased expression of IFN-g, TGF-b1, and IL-4. Post-challenge, IFN-g and IL-12B expression declined in vaccinated animals, but TGF-b1 persisted. High pre challenge IgG, IFN-g, and TGF-b1 were associated with protection, whereas increased IL-12B post-challenge was associated with disease severity. Discussion: These findings demonstrate a coordinated interplay between humoral and cellular immune responses in vaccine-induced protection, with IFN-g emerging as a potential biomarker in conjunction with antibody titre. The study provides a deeper further understanding on the immune mechanisms underlying vaccine-mediated protection against C. chauvoei and shall be relevant for the development of more effective vaccines.