Adjuvant Synergy: Alum and chlorogenic acid enhance Th1 responses and survival in a Salmonella typhimurium challenge model

Alum adjuvants do not induce Th1 responses with killed microorganisms, although Th1 responses are crucial for defending against intracellular microbes. Chlorogenic acid (CGA) can shift immune responses from Th2 toward Th1. This study assessed the benefits of combining CGA with alum on cellular and humoral immunity following immunization with a heat-killed preparation of Salmonella typhimurium (HKST). Male Balb/c mice received two doses of the HKST vaccine, with or without alum, CGA, or both, administered two weeks apart. Immune responses and protection against S. typhimurium were evaluated two weeks after the final dose.The alum and CGA combination enhanced the HKST vaccine's ability to stimulate lymphocyte proliferation, delayed-type hypersensitivity reactions, and antibody titers, and alter the ratio of IgG2a/IgG in favor of IgG2a. These findings correlated with a shift toward a Th1 immune response and improved protective immunity against S. typhimurium. Also, the group receiving the combined adjuvant had a longer survival rate following exposure to the acute dose of S. typhimurium and had a lower bacterial load in the liver when exposed to the subacute dose of S. typhimurium compared to other immunization protocols. Overall,the combined alum and CGA significantly boosted cellular and humoral immunity following HKST immunization.