Hydrophobic Mycobacterial Antigens Elicit Polyfunctional T Cells in Immunized Cattle: Association With Protection Against Challenge?

Bovine tuberculosis (bTB), caused by , is a chronic disease of cattle with a detrimental impact on food quality and production. Research on bTB vaccines has predominantly been focused on proteinaceous antigens. However, mycobacteria have a thick and intricate lipid outer layer and lipids as well as lipopeptides are important for immune-evasion and virulence. In humans, lipid extracts of have been shown to elicit immune responses effective against . Chloroform-methanol extraction (CME) was applied to BCG to obtain a hydrophobic antigen extract (CMEbcg) containing lipids and lipopeptides. CMEbcg stimulated IFN-γIL-2 and IL-17AIL-22 polyfunctional T cells and elicited T cell responses with a Th1 and Th17 cytokine release profile in both BCG vaccinated and challenged calves. Lipopeptides were shown to be the immunodominant antigens in CMEbcg, stimulating CD4 T cells MHC class II. CMEbcg expanded T cells killed CMEbcg loaded monocytes and the CMEbcg-specific CD3 T cell proliferative response following BCG vaccination was the best predictor for reduced pathology following challenge with . Although the high predictive value of CMEbcg-specific immune responses does not confirm a causal relationship with protection against challenge, when taking into account the antimycobacterial phenotype of CMEbcg-specific T cells (e.g. Th1/Th17 cytokine profile), it is indicative that CMEbcg-specific immune responses could play a functional role in immunity against . Based on these findings we conclude that lipopeptides of are potential novel subunit vaccine candidates and that further studies into the functional characterization of lipopeptide-specific immune responses together with their role in protection against bovine tuberculosis are warranted.