Impact of adjuvants on innate and adaptive immune responses to Lawsonia intracellularis antigens in pigs when administered via the intradermal route

The purpose of this study was to evaluate how the immune response to recombinant antigens is impacted by formulation with a panel of Montanide adjuvants Montanide IMS 1313 VG NST (M1313), Montanide ISA 660 VG (M660) and Montanide Gel 02 (MGel02) administered intradermally (ID) to pigs in combination with four antigens - FliC, ClpP, GroEL and YopN (Ag), which were previously found to be immunogenic when administered to pigs via the intramuscular route. M660, MGel02 and M1313 plus Ag formulations induced significantly elevated serum anti-ClpP IgG, anti-GroEL or anti-FliC IgG titres relative to pigs administered their respective adjuvants alone. Further, M660, MGel02, and M1313 plus Ag formulations contributed to significantly elevated anti-ClpP IgG, and anti-FliC IgG titres in serum, over time. No significant mucosal IgA titers were detected. Pigs administered the ID subunit vaccine formulated with M660 showed significantly elevated antigen-specific IFNγ secretion, a marker of a strong cell-mediated immune response, but these animals also developed lesions at the site of injection accompanied by evidence of significant suppurative inflammation. In a second study, histological analysis after 7 days or 24 h showed significantly increased granuloma formation, cellular recruitment, suppurative inflammation and necrosis, with reduced evidence of these pathologies in response to M660 alone. The tissue site reactions showed significantly elevated IL-1β, but not IL-6 or IFNγ, protein expression. Further, results showed significantly elevated CXCL2 gene expression between 24 h and 7 days, but not differential expression of NLRP3 or MSR1 genes, despite these genes being known to contribute to elevated IL-1β secretion and the associated pathology. The elevated expression of CXCL2 expression observed in the M660 + Ag group shows agreement with the neutrophil infiltration observed in the histopathology, which is consistent with neutrophil recruitment and involvement. These studies indicate that M660 + Ag contribute to humoral and cell-mediated immunity, but reduced doses should be assessed to ensure immunity without site reactions.