Leptospiral Outer Membrane Proteins OmpL1 and LipL41 Exhibit Synergistic Immunoprotection

Abstract

New vaccine strategies are needed for prevention of leptospirosis, a widespread human and veterinary disease caused by invasive spirochetes belonging to the genus Leptospira. We have examined the immunoprotective capacity of the leptospiral porin OmpL1 and the leptospiral outer membrane lipoprotein LipL41 in the Golden Syrian hamster model of leptospirosis. Specialized expression plasmids were developed to facilitate expression of leptospiral proteins inEscherichia coli as the membrane-associated proteins OmpL1-M and LipL41-M. Although OmpL1-M expression is highly toxic inE. coli, this was accomplished by using plasmid pMMB66-OmpL1, which has undetectable background expression without induction. LipL41-M expression and processing were enhanced by altering its lipoprotein signal peptidase cleavage site to mimic that of the murein lipoprotein. Active immunization of hamsters with E. coli membrane fractions containing a combination of OmpL1-M and LipL41-M was found to provide significant protection against homologous challenge with Leptospira kirschneri serovar grippotyphosa. At 28 days after intraperitoneal inoculation, survival in animals vaccinated with both proteins was 71% (95% confidence interval [CI], 53 to 89%), compared with only 25% (95% CI, 8 to 42%) in the control group (P < 0.001). On the basis of serological, histological, and microbiological assays, no evidence of infection was found in the vaccinated survivors. The protective effects of immunization with OmpL1-M and LipL41-M were synergistic, since significant levels of protection were not observed in animals immunized with either OmpL1-M or LipL41-M alone. In contrast to immunization with the membrane-associated forms of leptospiral proteins, hamsters immunized with His6-OmpL1 and His6-LipL41 fusion proteins, either alone or in combination, were not protected. These data indicate that the manner in which OmpL1 and LipL41 associates with membranes is an important determinant of immunoprotection.

Outer membrane proteins of pathogenic spirochetes

“…Hence, in this study no vaccine synergy was noted when an outer membrane lipoprotein (LipL32/ Hap-1) and a transmembrane OMP (OmpL1) were administered together. This lends credence to the hypothesis that the synergy observed in the study by Haake et al [185], was a result of a specific interaction between LipL41 and OmpL1. However, the adenovirus-encoded LipL32/Hap-1 and OmpL1 would undoubtedly not contain the post-translational lipid modification and any conformational epitopes, which are likely to be associated with the membrane forms of these proteins, and which were found to be critical for immunoprotection in the study performed by Haake et al [185].…”

“…Co-administration of the surface-exposed leptospiral OMPs OmpL1 and LipL41 was shown to mediate partial synergistic immunoprotection in the hamster model of leptospirosis [185]. In contrast to the vaccine synergism observed between OspA and DbpA [241], neither leptospiral antigen alone was able to elicit protective immunity.…”

Molecular cloning and characterization of a novel leptospiral lipoprotein with OmpA domain

“…This result suggests that leptospiral protein(s) can be candidates for a new vaccine that prevents infection with a broad spectrum of Leptospira . Some outer membrane proteins of Leptospira , lipoproteins LipL32 (also known as Hap1), LipL41 and the porin OmpL1, have been found to be protective immunogens that are conserved among various pathogenic leptospires [3–7].…”

Genetic differences among the LPS biosynthetic loci of serovars of Leptospira interrogans and Leptospira borgpetersenii

“…Furthermore, leptospiral LPS elicits the production of agglutinating, opsonic, protective antibodies in mice, hamsters and humans [2^4]. Even though a protective role for OmpL1 and LipL41 outer membrane proteins in leptospirosis has been reported [5], LPS is considered the main protective antigen identi¢ed thus far in leptospires [6]. There are no data describing the structure of the LPS of Leptospira that would explain the serological diversity in this species.…”