Preparation of lentinan-calcium carbonate microspheres and their application as vaccine adjuvants

Adjuvants improve vaccine potency by enhancing immunogenicity and sustaining long-term immune responses. Lentinan (LNT), a beta-1,3-glucohexaose with beta-1,6-branches, is extracted from the mushroom Lentinus edodes and functions as an effective immunostimulatory drug. Previous studies have demonstrated the adjuvant activity of calcium carbonate (CaCO3) microspheres as well as their use as antigen delivery systems. In this study, we successfully loaded CaCO3 microspheres with LNT and evaluated their physicochemical characteristics prior to the adsorption of ovalbumin. Our experimental results demonstrated that LNT-CaCO3 significantly enhanced lymphocyte proliferation, and boosted the frequency of CD69 + B cells and the ratio of CD4+ to CD8 + T cells in spleen lymphocytes. Moreover, LNT-CaCO3 unexpectedly induced the secretion of IgG and Th-associated cytokines (IL-2, IL-4, IFN-gamma, and TNF-alpha) in immunized mice. Therefore, LNT-CaCO3 microspheres induce robust cellular and humoral immune responses and have potential utility as vaccine delivery systems.