The trehalose glycolipid C18Brar promotes antibody and T-cell immune responses to <i>Mannheimia haemolytica</i> and <i>Mycoplasma ovipneumoniae</i> whole cell antigens in sheep

Bronchopneumonia is a common respiratory disease in livestock. <i>Mannheimia haemolytica</i> is considered the main causative pathogen leading to lung damage in sheep, with <i>Mycoplasma ovipneumoniae</i> and ParaInfluenza virus type 3, combined with adverse physical and physiological stress, being predisposing factors. A balance of humoral and cellular immunity is thought to be important for protection against developing respiratory disease. In the current study, we compared the ability of the trehalose glycolipid adjuvant C18Brar (C18-alkylated brartemicin analogue) and three commercially available adjuvant systems <i>i</i>.<i>e</i>., Quil-A, Emulsigen-D, and a combination of Quil-A and aluminium hydroxide gel, to stimulate antibody and cellular immune responses to antigens from inactivated whole cells of <i>M</i>. <i>haemolytica</i> and <i>M</i>. <i>ovipneumoniae</i> in sheep. C18Brar and Emulsigen-D induced the strongest antigen-specific antibody responses to both <i>M</i>. <i>haemolytica</i> and <i>M</i>. <i>ovipneumoniae</i>, while C18Brar and Quil-A promoted the strongest antigen-specific IL-17A responses. The expression of genes with known immune functions was determined in antigen-stimulated blood cultures using Nanostring nCounter technology. The expression levels of <i>CD40</i>, <i>IL22</i>, <i>TGFB1</i>, and <i>IL2RA</i> were upregulated in antigen-stimulated blood cultures from animals vaccinated with C18Brar, which is consistent with T-cell activation. Collectively, the results demonstrate that C18Brar can promote both antibody and cellular responses, notably Th17 immune responses in a ruminant species.