Immunological characteristics of the glycolipid antigen of Leptospira interrogans serovar lai

Advances & challenges in leptospiral vaccine development

Considerable progress has been made in the field of leptospiral vaccines development since its first use as a killed vaccine in guinea pigs. Despite the fact that the immunity conferred is restricted to serovars with closely related lipopolysaccharide antigen, certain vaccines have remained useful, especially in endemic regions, for the protection of high-risk individuals. Other conventional vaccines such as the live-attenuated vaccine and lipopolysaccharide (LPS) vaccine have not gained popularity due to the reactive response that follows their administration and the lack of understanding of the pathogenesis of leptospirosis. With the recent breakthrough and availability of complete genome sequences of Leptospira, development of novel vaccine including recombinant protein vaccine using reverse vaccinology approaches has yielded encouraging results. However, factors hindering the development of effective leptospiral vaccines include variation in serovar distribution from region to region, establishment of renal carrier status following vaccination and determination of the dose and endpoint titres acceptable as definitive indicators of protective immunity. In this review, advancements and progress made in LPS-based vaccines, killed- and live-attenuated vaccines, recombinant peptide vaccines and DNA vaccines against leptospirosis are highlighted.

Protein typing of major outer membrane lipoproteins from Chinese pathogenic Leptospira spp. and characterization of their immunogenicity

Leptospirosis, caused by different Leptospira species, is one of the most widespread zoonotic infections worldwide. Here we expressed three major leptospiral lipoproteins and examined their immunogenicity. All the pathogenic Leptospira strains tested possess the lipL21, lipL32 and lipL41 genes, but the latter two can be further divided into different gene types (lipL32-1, lipL32-2, lipL41-1, lipL41-2). Microscopic agglutination test revealed that rLipLs antisera had extensive cross-immunoagglutination among the 178 leptospiral strains in which rLipL32-1 contributed the highest agglutination titer. The rLipLs-based ELISAs established in this study demonstrated that in the sera of 385 leptospirosis patients infected with different serovars of Leptospira interrogans, rLipL32-1 had the highest positive rates for IgG and IgM (89.4-98.7%), followed by the IgG/IgM positive rates of rLipL21 (87.0-96.1%) and rLipL32-2 (86.5-96.9%), while the two rLipL41s presented the lowest IgG/IgM positive rates (69.9-83.9%). The immunoprotective levels in guinea pigs of rLipL32-1 (58.3% and 66.7%) were the highest, compared to those of the other rLipLs (25.0-58.3%). Multiple different rLipLs would increase immunoprotective levels (from 58.3% and 66.7% to 83.3% and 91.7%). The data suggest that all the rLipLs are the genus-specific superficial antigens of pathogenic Leptospira species and should be considered in designing universal vaccines against leptospirosis.

Leptospirosis vaccines

Leptospirosis is a serious infection disease caused by pathogenic strains of the Leptospira spirochetes, which affects not only humans but also animals. It has long been expected to find an effective vaccine to prevent leptospirosis through immunization of high risk humans or animals. Although some leptospirosis vaccines have been obtained, the vaccination is relatively unsuccessful in clinical application despite decades of research and millions of dollars spent. In this review, the recent advancements of recombinant outer membrane protein (OMP) vaccines, lipopolysaccharide (LPS) vaccines, inactivated vaccines, attenuated vaccines and DNA vaccines against leptospirosis are reviewed. A comparison of these vaccines may lead to development of new potential methods to combat leptospirosis and facilitate the leptospirosis vaccine research. Moreover, a vaccine ontology database was built for the scientists working on the leptospirosis vaccines as a starting tool.

Serological analysis of human leptospirosis in the Philippines

Leptospirosis in the Philippines is an underrepresented disease. To achieve an accurate means of serodiagnosis, we demonstrated antibodies to the prevalent Leptospira serovars in sera of 71 patients from three major hospitals in Manila by the microscopic agglutination test and Western blot analysis. Sera of 53 patients contained antibody against 8 serovars poi, tarassovi, manilae, pyrogenes, australis, grippotyphosa, javanica, and autumnalis.

Control of immunologically crossreactive leptospiral infection by administration of lipopolysaccharides from a nonpathogenic strain of Leptospira biflexa

In our previous paper (Matsuo, K., Isogai, E., and Araki, Y., Carbohydr. Res., 328: 517-524, 2000), antigenic polysaccharides obtained from the lipopolysaccharide (LPS) fraction of a nonpathogenic leptospira, Leptospira biflexa patoc Patoc I, are shown to be broadly crossreactable with most rabbit antisera elicited by immunization with various pathogenic leptospires. The result led us to test a protective effect of the same LPS in a hamster model system by heterologously challenging with a pathogenic leptospira, L. interrogans manilae UP-MMG. Firstly, a similarity in the antigenic epitopes of L. biflexa and L. interrogans was confirmed by the following assays. In the microscopic agglutination test (MAT), a hamster antiserum elicited by immunization with the L. biflexa-LPS preparation was shown to agglutinate cells of L. interrogans. Contrarily, in the enzyme-linked immunosorbent assay (ELISA), the L. biflexa-LPS preparation was shown to crossreact with a hamster antiserum elicited by immunization with whole cells of L. interrogans. These results suggest that the same or closely related antigens may be present on the cell surfaces of both L. biflexa patoc Patoc I and L. interrogans manilae UP-MMG. Furthermore, in a protective assay, the prior administration of a L. biflexa-LPS preparation resulted in raising a protective response in hamsters against challenge by L. interrogans without any side effect. The protective effect was strongly dependent on the dose amounts and/or administration times of L. biflexa-LPS. Thus, L. biflexa-LPS preparations can use as a potent vaccine against leptospirosis caused by various leptospires.

Evidence of cross-protection within Leptospira interrogans in an experimental model

Killed whole-cell preparations were used as bacterins against leptospirosis. As this type of protection is considered to be serogroup-specific, several serogroups were added to the usual vaccines, and the most pathogenic serovar was chosen for each group. Different leptospire extracts were evaluated for their protective capacity against acute lethal leptospirosis in gerbils (Meriones unguiculatus). Total extracts induced complete protection against homologous challenges and partial protection against heterologous challenges. LPS fractions protected against homologous but not heterologous challenges, whereas protein extract induced significant protection against both types of challenge. Thus, cross-protection within L. interrogans was related to the protein extract.

Immunochemical characteristics and localization on cells of protective antigen (PAg) prepared from Leptospira interrogans serovar lai

Immuno-electron microscopic methods revealed that the protective antigen (PAg) of Leptospira interrogans serovar lai exists on the outer envelope sheathing the leptospiral cell body. PAg lost its protective activity after treatment by hydrolysis with 2 M formic acid at 100 C for 2 hr, or oxidation with periodate at 4 C for 40 hr. The antigenic oligosaccharide fraction was further purified from the hydrolyzed PAg by immunoaffinity column coupled with protective monoclonal antibody, LW2, and by gel filtration of HPLC. The antigenic oligosaccharide fraction contained two unknown sugars and 4-O-methylmannose (molar ratio 3:5:1). These findings suggested that these sugars are components of an antigenic determinant contributing to the protective immunity against serovar lai infection.

Reactivity of neuroborreliosis patients (Lyme disease) to cardiolipin and gangliosides

A subset of patients (50%) with neuroborreliosis (Lyme disease) showed IgG reactivity to cardiolipin in solid phase ELISA. In addition, a subset of patients with neuroborreliosis (29%) and syphilis (59%) had IgM reactivity to gangliosides with a Gal(beta 1-3) GalNac terminal sequence (GM1, GD1b, and asialo GM1). Anti-ganglioside IgM antibodies were significantly more frequent in these two groups of patients compared to patients with cutaneous and articular Lyme disease, primary antiphospholipid syndrome, systemic lupus erythematosus and normal controls. Correlative evidence and adsorption experiments indicated that antibodies to cardiolipin had separate specificities from those directed against the gangliosides. IgM antibodies to Gal(beta 1-3) GalNac gangliosides appeared to have similar specificities since these were positively correlated and inhibitable by cross adsorption assays. Given the clinical associations of patients with neuroborreliosis and syphilis with IgM reactivity to gangliosides sharing the Gal(beta 1-3) GalNac terminus, we suggest that these antibodies could represent a response to injury in neurological disease or a cross reactive event caused by spirochetes.

Protective activity of antisera against isolates of Borrelia burgdorferi from various geographical origins

Antisera from rabbits immunized with two Japanese strains of Borrelia burgdorferi, HP3 an isolate from Ixodes persulcatus and HO14 an isolate from I. ovatus, or the European strain P/Bi isolated from human cerebrospinal fluid (CSF) did not passively protect hamsters from challenge with the infectious strain 297, a North American isolate from patient CSF. Antisera to strains 297 and B31, a North American isolate from I. dammini, however, provided protective effect to challenge with strain 297. Immune mice sera in the presence of homologous B. burgdorferi antigen induced the production of oxygen intermediates from mouse peritoneal exudate cells. Heterologous B. burgdorferi antigen had no effect. These results suggest that antigenic properties of Japanese strains are different from those of North American and European isolates.

Immunological properties of Borrelia burgdorferi isolated from the Ixodes ovatus in Shizuoka, Japan

Three strains of spirochetes (IKA1 to 3) were isolated from the midgut of Ixodes ovatus collected in the Ikawa region of the northern part of Shizuoka, Japan. These isolates had eight flagella, and their size and other morphological features were similar to Borrelia burgdorferi. They showed similar motility and reacted with monoclonal antibody (MAb) H9724 against borrelial flagella and with MAb H5332 against the outer surface protein A. These strains showed similar SDS-PAGE profiles to that of B. burgdorferi strain B31 and P/Bi isolated in the U.S.A. and Europe, respectively. Immunoblot with Lyme disease patient serum showed positive reactions with the flagella (41 Kilodalton, kDa), protein C (20 to 22 kDa), and outer surface protein A (29 kDa) of the isolates. Immunological properties, morphological characteristics, and epidemiological features revealed that these isolates were B. burgdorferi.

Antigenic properties of Borrelia burgdorferi isolated from Ixodes ovatus and Ixodes persulcatus in Hokkaido, Japan

Spirochete strains HP3 and HO14, isolated from Ixodes persulcatus and I. ovatus in Hokkaido in 1989, were the first isolates of Borrelia burgdorferi, the etiological agent of Lyme disease, to be recognized in Japan. Antigenic properties of the Japanese strains were compared with those of the strains isolated in the United States (B31 and 297) and Europe (IRS, P/Gau, P/Bi, 2/B45, and 3/B56) by Western blotting (immunoblotting), by using monoclonal antibodies (MAbs) against strains B31 and P/Bi. The Japanese strains reacted with MAb U40 against the 41-kDa antigen. MAb E34a31 against Osp A reacted with all the strains tested except for strain HP3. Furthermore, MAb U31b against Osp A reacted with all the American and European strains but did not react with the Japanese strains. When MAbs against Osp B were used, MAb E34b reacted only with European strains and MAb U34b reacted only with the American strains. However, neither showed reactivity to two Japanese strains. MAb E60 against 60-kDa antigen reacted with all the U.S. and European strains and strain HP3 but did not react with Japanese strain HO14. These results indicate that the antigenicity of the Japanese strains isolated from two species of ixodid ticks is different from that of the strains isolated in the United States and Europe. It is suggested that the Japanese strains are much more suitable than the U.S. or European strains as the antigen source for the serodiagnosis of Lyme disease in Japan.

Characterization of outer membrane and secreted proteins of Leptospira interrogans serovar pomona

Outer membrane and secreted proteins were isolated from Leptospira interrogans serovar pomona and characterized by sodium dodecyl sulfate polyacrylamide gel electrophoresis, immunoblot and radioimmunoprecipitation techniques. The L. interrogans outer membranes were extracted with Triton X-114 and contained several proteins. The major cellular protein with a molecular mass of 31 kDa was associated exclusively with the L. interrogans outer membrane. Using a whole cell immunoprecipitation method, five hydrophobic, Triton X-114 extractable proteins (22, 26, 31, 36 and 42 kDa) were exposed on the surface of L. interrogans. The 31 kDa protein was heat labile and was a potent antigen in animals experimentally infected with L. interrogans serovar pomona. Several proteins were secreted by L. interrogans including a 60 kDa protein tentatively identified as the L. interrogans hemolysin.

Comparison of protective effects with tetra-valent glycolipid antigens and whole cell-inactivated vaccine in experimental infection of Leptospira

The protective antigens (PAgs), glycolipid substance, were extracted from Leptospira interrogans serovars autumnalis, hebdomadis, australis and copenhageni, which were considered as main causal serovars of human leptospirosis in Japan, with chloroform-methanol-water (1:2:0.8, [vol/vol/vol]) solution. The tetra-valent formalin-inactivated leptospiral vaccine (Weil's disease and Akiyami combined vaccine) composed of the four serovars mentioned are used as vaccine to protect human from leptospiral infection in Japan. The protective effect, agglutinating antibody-inducing activity and opsonin-inducing activity of tetra-valent PAgs were compared with those of vaccines now in use, which were supplied by two companies, Takeda Chemical Industries, Ltd., and Denka-Seiken Co., in Japan. The tetra-valent PAgs which contained 10 micrograms of each PAg protected hamsters and cyclophosphamide-treated mice from lethal infection of serovar copenhageni and induced agglutinating antibodies against the four serovars in the same degrees as vaccines. These results suggested that the tetra-valent PAgs might be useful as a component vaccine against leptospiral infection instead of formalized whole cells vaccines for human.

Changes in the surface of Leptospira interrogans serovar grippotyphosa during in vitro cultivation

Surface components of virulent and attenuated Leptospira interrogans serovar grippotyphosa were compared by using Triton X-114 solubilization and phase partitioning, immunoprecipitation of intact organisms, and freeze-fracture electron microscopy. Removal of the leptospiral outer membrane by using 0.1% Triton X-114 was demonstrated by whole-mount electron microscopy and by essentially complete solubilization of a lipopolysaccharidelike substance (LLS) from the outer membrane. Triton X-114 (0.1%) did not solubilize subsurface proteins, such as endoflagellar filaments or penicillin-binding proteins, which are markers for the periplasmic space and inner membrane, respectively. Triton X-114 solubilized material from both the virulent and attenuated strains, which partitioned into the hydrophobic, detergent phase, contained LLS and major proteins of 41 and 44 kDa, which were also immunoprecipitable from intact organisms. The virulent strain contained greater amounts of an LLS component with an apparent molecular mass of 30 kDa (R(f) = 0.57), whereas the attenuated strain contained larger amounts of an LLS component with an apparent molecular mass of 20 kDa (R(f) = 0.74). Differences in protein components between virulent and attenuated organisms were also detected; whereas the 41- and 44-kDa proteins were immunoprecipitated in equal amounts from both the virulent and attenuated strains, a 33-kDa protein was immunoprecipitated in significantly greater amounts from the attenuated strain. Quantitation of outer membrane particle density by freeze-fracture electron microscopy showed that both strains had a low transmembrane outer membrane protein content compared with that of typical gram-negative bacteria. The virulent and attenuated strains had 443 and 990 particles (P less than 0.000001) per micron, respectively, in the concave outer membrane fracture face. These findings suggest that in vitro cultivation of L. interrogans is accompanied by quantitative and qualitative changes in both LLS and outer membrane-associated proteins.

Biological activities and endotoxic activities of protective antigens (PAgs) of Leptospira interrogans

The biological and endotoxic activities of protective antigens (PAgs) prepared by the chloroform-methanol-water method from Leptospira interrogans serovars lai, copenhageni and canicola were examined. The PAg preparations did not show a local Shwartzman reaction in the rabbits at doses of 100 micrograms and 50 micrograms/site and lethal toxicity to galactosamine-sensitized mice at the dose of 12.5 micrograms to 50 micrograms/mouse. PAgs exhibited a weak cytotoxic action on peritoneal exudate macrophages of C3H/HeJ and C3H/HeN mice at the dose of 500 micrograms/ml in vitro, but did not show cytotoxicity for BHK-21 cells kidney cells of the Syrian hamster, CHO-K1, ovary cells of the Chinese hamster, and CHL, lung cells of the Chinese hamster, at doses of 5 and 500 micrograms/ml. Gelation activity in the Limulus test was only observed at PAg concentrations over 100 ng/ml, which dose was 10,000 times that of lipopolysaccharide (LPS) of Escherichia coli O55:B5. Furthermore, an adjuvant activity of PAgs was not observed in the production of anti-sheep red blood cell antibody in mice. Mitotic conversion of spleen cells from C3H/HeJ and C3H/HeN mice was observed by the addition of PAgs in vitro. These results indicated that the biological properties of PAgs were different from those of LPS prepared from gram-negative enterobacteria, that PAgs had no endotoxic activity and that the biological safety of PAgs as vaccine was proved.

Heat stability of protective antigen of Leptospira interrogans serovar lai

Protective antigen (PAg; glycolipid antigen; molecular size, 23 to 30 kilodaltons), the serogroup-specific antigen partially purified from leptospiral cells, is one of the most important protective antigens. The heat stability of PAg was compared with that of whole-cell (WC) antigen by using sodium dodecyl sulfate-polyacrylamide gel electrophoresis, immunoblotting, protective activity, opsonin-inducing activity, agglutinating antibody-inducing activity, and an inhibition test in an enzyme-linked immunosorbent assay. A band of 23 to 30 kilodaltons of PAg, which was seen in untreated PAg and WC, shifted to a position with a molecular size of ca. 20 kilodaltons after heat treatment of PAg at 80 degrees C for 30 min and WC at 100 degrees C for 30 min. In the enzyme-linked immunosorbent assay inhibition test with monoclonal antibody LW2 and a sonicated antigen of WC, the inhibition rate of PAg and WC to sonicated WC was reduced by heat treatment at 80 degrees C for 30 min and at 100 degrees C for 30 min, respectively. Agglutinating antibody-inducing activities and opsonin-inducing activities of PAg and WC in mice were reduced by heat treatment under the same conditions; these activities were assayed by a microscopic agglutination test and by chemical luminescence response in serum from immunized mice, respectively. Protective activity of heated PAg and heated WC in cyclophosphamide-pretreated mice agreed with the results of immunogenicity in mice. These results indicate that the Leptospira PAg is one of the important protective antigens and is altered by heat treatment at 80 degrees C. Furthermore, the immunogenicity and antigenicity of the PAg present in WC are more stable than that of the extracted PAg, and the coexistence of other cellular components with PAg might protect and stabilize PAg from the heat treatment.

Immunological reactivity and passive protective activity of monoclonal antibodies against protective antigen (PAg) of Leptospira interrogans serovar lai

Monoclonal antibody (MAb) AG1 against the protective antigen (PAg) was produced and characterized. It had been extracted from Leptospira interrogans serovar lai by the chloroform-methanol-water method and was of glycolipid nature (23-30Kd). The fact that the PAg was a serogroup-specific antigen was shown by MAb AG1, because MAb AG1 agglutinated serovars of serogroup Icterohaemorrhagiae. Purified MAb LW2 and LW3 which are agglutinating antibodies of serovar lai and AG1 passively protected hamsters from leptospiral infection. Induction of the reactive oxygen intermediates by MAbs from peritoneal exudate macrophages of mice were observed in the chemical luminescence assay and the MAbs reacted with the PAg in the dot enzyme-linked immunosorbent assay. However, MAb LW4a against the genus-specific antigen present in the sub-surface of leptospiral cells did not show protective and reactive-oxygen-inducing activities; they reacted with the non-protective glycolipid antigen of low molecular weight (Fr I, 10-15Kd) in the dot enzyme-linked immunosorbent assay. These results indicated that anti-PAg antibody exhibited opsonic activity against Leptospira and the production of reactive oxygens by macrophages led to leptospiricidal action as one of the defence mechanisms of the host against leptospiral infection. However, the antibody against the genus-specific glycolipid antigen may not be important for protection against leptospiral infection.