[ODP-179] Effect of eggshell-derived hydroxyapatite on mucosal vaccine using bacterial vesicles
The mRNA vaccines in intramuscular injection have been used to prevent COVID-19. However, to prevent the infection completely, induction of mucosal immunity is indispensable. Thus, we evaluated the nano-size hydroxyapatite (HA) derived from eggshells (EHA) as a mucosal adjuvant to develop effective mucosal vaccine. We nasally immunized mice with vesicles from Streptococcus mutans UA159 as model antigens together with the EHA or polyriboinosinic polyribocytidylic acid [poly(I-C)]. The second, third, fourth, and fifth immunization were performed 3, 5, 7, and 9 weeks after the first immunization, respectively. Nasal immunization of vesicles and 1 μg of EHA increased vesicle-specific plasma IgG as compared with those of mice given vesicle alone after third immunization; however, two groups showed similar IgG responses after fifth immunization. Mice given vesicle and 100 μg of EHA increased vesicle-specific salivary IgA after third immunization at levels similar to positive control group given the vesicles and poly I-C, although there were not advantages using EHA after fifth immunization. These results suggest that EHA has adjuvanticity in immunization less than 4 times. Further, although the effective dose of the EHA in the induction of systemic IgG and mucosal IgA responses were different, the EHA preferentially enhances mucosal immunity in response to S. mutans vesicles.