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

Vaccines against leptospirosis

Vaccines against leptospirosis followed within a year of the first isolation of Leptospira, with the first use of a killed whole cell bacterin vaccine in guinea pigs published in 1916. Since then, bacterin vaccines have been used in humans, cattle, swine, and dogs and remain the only vaccines licensed at the present time. The immunity elicited is restricted to serovars with related lipopolysaccharide (LPS) antigen. Likewise, vaccines based on LPS antigens have clearly demonstrated protection in animal models, which is also at best serogroup specific. The advent of leptospiral genome sequences has allowed a reverse vaccinology approach for vaccine development. However, the use of inadequate challenge doses and inappropriate statistical analysis invalidates many of the claims of protection with recombinant proteins.

Characterization of a lipopolysaccharide mutant of Leptospira derived by growth in the presence of an anti-lipopolysaccharide monoclonal antibody

A lipopolysaccharide mutant of Leptospira interrogans (LaiMut) was obtained by growth in the presence of an agglutinating monoclonal antibody (mAb) against lipopolysaccharide. Agglutination reactions with anti-lipopolysaccharide mAbs and polyclonal antibodies showed that LaiMut had lost some serogroup Icterohaemorrhagiae agglutinating epitopes. However, LaiMut displayed an increased reactivity to antisera against related serogroups, suggesting that the disruption of some lipopolysaccharide epitopes resulted in greater exposure to cross-reactive epitopes, not accessible to antibodies in the wild type (LaiWT). Comparison of the nucleotide sequences of the lipopolysaccharide loci of LaiMut and Lai wild type (LaiWT) strains showed an inframe stop mutation in the gene encoding undecaprenyl-galactosyltransferase, a protein that provides a fundamental and nonredundant function essential for lipopolysaccharide biosynthesis. Despite this, the biosynthesis of lipopolysaccharide agglutinating antigens was not abolished by the mutation. Based on the phenotype of LaiMut and analysis of the domain structure of the undecaprenyl-galactosyltransferase in relation to the mutation, we propose that the mutation results in the expression of two functional proteins in place of the undecaprenyl-galactosyltransferase. We hypothesize that the loss of coordination of the coupled function afforded by the intact dual function protein present in the parent strain results in an inefficient production of lipopolysaccharide in LaiMut.

Review paper: Host-pathogen interactions in the kidney during chronic leptospirosis

Pathogenic species of Leptospira cause leptospirosis, a global zoonotic disease. Leptospira colonize renal tubules of chronically infected maintenance hosts, from where they are shed in urine to the environment and survive in suitable moist conditions. Transmission of disease to new hosts is facilitated by contact with contaminated urine or water sources, because Leptospira can penetrate broken skin or mucosal surfaces of new hosts. Infection of new hosts may be asymptomatic, as with chronically infected maintenance hosts, or may result in an acute disease process in which clinical signs can include fever, jaundice, renal failure, and pulmonary hemorrhage. Those factors that determine if an animal will suffer an acute or a chronic infection are not fully understood but include host animal species, infecting serovar, and infecting dose. During chronic infection, renal colonization and leptospiruria persist despite cellular and humoral responses by the host. Tubulointerstitial nephritis is the most common lesion associated with chronic infection, and this may progress to fibrosis and subsequent renal failure. This review aims to address how Leptospira cause tubulointerstitial nephritis during chronic leptospirosis and to summarize the mechanisms by which Leptospira might evade host immune responses during chronic colonization of the renal tubule.

Changes in lipopolysaccharide O antigen distinguish acute versus chronic Leptospira interrogans infections

Leptospirosis is the most geographically widespread zoonotic disease in the world. A severe pulmonary form of leptospirosis (SPFL) is being recognized with increased frequency. We have reported that human SPFL isolates of Leptospira cause acute lethal infection with prominent pulmonary hemorrhage in guinea pigs. We have found that the same SPFL strains cause asymptomatic infection and chronic renal shedding in rats, where infection is restricted to the renal tubules. To address the antigenic composition of host tissue-derived Leptospira (HTL), motile leptospires were purified from guinea pig liver by centrifugation on Percoll density gradients and compared to Percoll-purified in vitro-cultivated Leptospira (IVCL). The lipopolysaccharide O antigen (Oag) content of guinea pig liver-derived HTL was markedly reduced compared to that of IVCL, as demonstrated both by immunoblotting with a monoclonal antibody that was serovar specific for Oag and by periodate-silver staining. Confocal microscopy of HTL in guinea pig liver and kidney with the Oag-specific monoclonal antibody provided further evidence that diminution of the Oag content occurred in situ during lethal infection. In contrast, the Oag content of HTL in chronically infected rat renal tubules was indistinguishable from that of IVCL. These findings suggest that there may be regulation of Oag synthesis by Leptospira specific to the animal host infected. The hypothesis that the Oag content is related to whether lethal infection or chronic renal tubular colonization occurs remains to be tested.

Leptospirosis

Leptospirosis is a worldwide zoonotic infection with a much greater incidence in tropical regions and has now been identified as one of the emerging infectious diseases. The epidemiology of leptospirosis has been modified by changes in animal husbandry, climate, and human behavior. Resurgent interest in leptospirosis has resulted from large outbreaks that have received significant publicity. The development of simpler, rapid assays for diagnosis has been based largely on the recognition that early initiation of antibiotic therapy is important in acute disease but also on the need for assays which can be used more widely. In this review, the complex taxonomy of leptospires, previously based on serology and recently modified by a genotypic classification, is discussed, and the clinical and epidemiological value of molecular diagnosis and typing is also evaluated.

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.

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.