Assessment of immune responses in mice after intranasal immunization using outer membrane vesicles derived from 3 different Gram-negative pathogens

Bacterial outer membrane vesicles (OMVs) were released from the cell surface of Gram-negative bacteria during normal bacterial growth. OMVs contained a wide range of virulence factors and antigens such as LPS and outer membrane proteins. We have already reported strong immunogenicity of OMVs of a periodontal pathogen Porphyromonas gingivalis in an intranasal vaccine mouse model. In the present study, we aimed to compare the immune responses against three different OMVs derived from Escherichia coli, Neisseria meningitidis as well as P. gingivalis. BALB/c mice were intranasally immunized twice by 1 μg of OMVs with Poly(I:C) adjuvant. Serum, nasal wash, saliva, and feces specimens were collected two week after 2^nd immunization and analyzed using whole-cell ELISA. Pathogen-specific IgG in sera were successfully elicited in all pathogen OMV models. OMVs of all tested pathogens could also elicit pathogen-specific s-IgA at mucosal surfaces of whole body. In addition, IgG subtype analysis revealed that IgG1 is predominant in P. gingivalis model, while IgG2a is predominant in E. coli and N. meningitidis models. The findings suggest that P. gingivalis OMV vaccine enhances type 2 immunity, in good agreement with the clinical observation that type 2 immunity is predominantly active in periodontal tissues of periodontitis patients. In conclusion, we suggest the general applicability of the intranasal immunization model for eliciting both systemic and mucosal immune responses against pathogens irrespective to the species type, although the type of immunity vary due to the type of OMVs.