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Abstract
The wide variety of pathogenic Leptospira serovars and the weak protection offered by the available vaccines encourage the search for protective immunogens against leptospirosis. We found that the secretin GspD of the type II secretion system (T2S) of Leptospira interrogans serovar Canicola was highly conserved amongst pathogenic serovars and was expressed in vivo during infection, as shown by immunohistochemistry. Convalescent sera of hamsters, dogs, and cows showed the presence of IgG antibodies, recognizing a recombinant version of this protein expressed in Escherichia coli (rGspDLC) in Western blot assays. In a pilot vaccination study, a group of eight hamsters was immunized on days zero and 14 with 50 µg of rGspDLC mixed with Freund’s incomplete adjuvant (FIA). On day 28 of the study, 1,000 LD50 (Lethal Dose 50%) of a virulent strain of Leptospira interrogans serovar Canicola (LOCaS46) were inoculated by an intraoral submucosal route (IOSM). Seventy-five percent protection against disease (p = 0.017573, Fisher’s exact test) and 50% protection against infection were observed in this group of vaccinated hamsters. In contrast, 85% of non-vaccinated hamsters died six to nine days after the challenge. These results suggest the potential usefulness of the T2S secretin GspD of Leptospira as a protective recombinant vaccine against leptospirosis.
Highlights
Leptospirosis is a neglected and widespread zoonosis caused by the pathogenic species of Leptospira.Humans are accidental hosts who acquire the infection always from an animal source
The rGspDLC protein was purified by Ni-affinity chromatography and concentrated by size exclusion up to 1 mg/mL using 30 kDa Amicon filter columns (MilliporeTM), and an estimated 60 to
Antiserum obtained from rabbits immunized four times with a suspension of the heat-inactivated L. interrogans serovar Canicola strain LOCaS46 reached a 1:12,800 antibody titer in the Vaccines 2020, 8, x FOR PEER REVIEW
Summary
Leptospirosis is a neglected and widespread zoonosis caused by the pathogenic species of Leptospira.Humans are accidental hosts who acquire the infection always from an animal source. Rodents are considered as the main source of infection to human populations in rural and suburban areas with poor sanitary conditions [1,2]. Available vaccines consist of cell suspensions of inactivated leptospires (bacterins), which have proved to be partially protective and limited to specific Leptospira serovars and not eliciting a long-lasting immunity. Immunity obtained with such a kind of vaccine is directed mainly towards leptospiral lipopolysaccharide (LPS), this being the main reason for their limited protection against disease caused by the specific serovars, those included in the bacterins formulation [5,6].
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