Oral immunization of rat with chromosomal expression LipL32 in attenuated Salmonella vaccine induces immune respond against pathogenic Leptospira.

PURPOSE: Leptospirosis caused by Leptospira spp. remains a global health problem. Available commercial leptospiral vaccines have shown an ineffective prevention for leptospiral infection. The aim of this study was to develop leptospirosis vaccine using recombinant attenuated Salmonella vaccine (RASV) as a platform. We expected that this vaccine has ability to continuous and strongly stimulate immune systems including protective mucosal, humoral, and cell mediated immunity in rat model.

MATERIALS AND

METHODS

In this study, we engineered RASV, NRSL32 strain containing chromosomal fusion between nucleotides encoding secretion signal of SPI-2 effector protein, SspH2 and gene encoding major pathogenic leptospiral outer membrane lipoprotein, LipL32. Subsequently, our modified RASV was oral vaccination to rat and blood samples were taken for assessment of immune responses.

RESULTS

Our Salmonella NRSL32 strain showed expression and secretion of SspH21-215-LipL32 recombinant protein via SPI-2 T3SS. After oral administration of NRSL32 strain to rats, significant titers of total immunoglobulin G (IgG) and immunoglobulin A against rLipL32 were observed in long period up to 77 days after vaccination. The stimulated antibody showed ability to specific bind with LipL32 protein on surface of pathogenic Leptospira spp. Additionally, the balance level of IgG2a/IgG1 ratio and level of interferon-γ and interleukin-4 secretion were detected.

CONCLUSION

The results showed that our RASV platform with chromosomal expression elicited effective immune responses to leptospiral antigen. Moreover, this platform was capable for simultaneous stimulation of Th1 and Th2-biased responses. Further investigation is necessary study of protective efficacy against leptospiral infection in animal models.