BACKGROUND: Lipopolysaccharides (LPS) are complex, amphipathic biomolecules that constitute the major surface component of Gram-negative bacteria. Leptospira, unlike other human-pathogenic spirochetes, produce LPS, which is fundamental to the taxonomy of the genus, involved in host-adaption and also the target of diagnostic antibodies. Despite its significance, little is known of Leptospira LPS composition and carbohydrate structure among different serovars. RESULTS: LPS from Leptospira interrogans serovar Copenhageni strain L1-130, a pathogenic species, and L. licerasiae serovar Varillal strain VAR 010, an intermediately pathogenic species, were studied. LPS prepared from aqueous and phenol phases were analyzed separately. L. interrogans serovar Copenhageni has additional sugars not found in L. licerasiae serovar Varillal, including fucose (2.7%), a high amount of GlcNAc (12.3%), and two different types of dideoxy HexNAc. SDS-PAGE indicated that L. interrogans serovar Copenhageni LPS had a far higher molecular weight and complexity than that of L. licerasiae serovar Varillal. Chemical composition showed that L. interrogans serovar Copenhageni LPS has an extended O-antigenic polysaccharide consisting of sugars, not present in L. licerasiae serovar Varillal. Arabinose, xylose, mannose, galactose and L-glycero-D-mannoheptose were detected in both the species. Fatty acid analysis by gas chromatography-mass spectrometry (GC-MS) showed the presence of hydroxypalmitate (3-OH-C16:0) only in L. interrogans serovar Copenhageni. Negative staining electron microscopic examination of LPS showed different filamentous morphologies in L. interrogans serovar Copenhageni vs. L. licerasiae serovar Varillal. CONCLUSIONS: This comparative biochemical analysis of pathogenic and intermediately pathogenic Leptospira LPS reveals important carbohydrate and lipid differences that underlie future work in understanding the mechanisms of host-adaptation, pathogenicity and vaccine development in leptospirosis.

A vaccine to prevent the transmission of malaria parasites from infected humans to mosquitoes is an important component for the elimination of malaria in the 21st century, yet it remains neglected as a priority of malaria vaccine development. The lead candidate for Plasmodium falciparum transmission-blocking vaccine development, Pfs25, is a sexual stage surface protein that has been produced for vaccine testing in a variety of heterologous expression systems. Any realistic malaria vaccine will need to optimize proper folding balanced against cost of production, yield, and potentially reactogenic contaminants. Here Chlamydomonas reinhardtii microalga-produced recombinant Pfs25 protein was formulated with four different human-compatible adjuvants (alum, Toll-like receptor 4 [TLR-4] agonist glucopyranosal lipid A [GLA] plus alum, squalene-oil-in-water emulsion, and GLA plus squalene-oil-in-water emulsion) and compared for their ability to induce malaria transmission-blocking antibodies. Alga-produced recombinant Pfs25 plus GLA plus squalene-oil-in-water adjuvant induced the highest titer and avidity in IgG antibodies, measured using alga-produced recombinant Pfs25 as the enzyme-linked immunosorbent assay (ELISA) antigen. These antibodies specifically reacted with the surface of P. falciparum macrogametes and zygotes and effectively prevented parasites from developing within the mosquito vector in standard membrane feeding assays. Alga-produced Pfs25 in combination with a human-compatible adjuvant composed of a TLR-4 agonist in a squalene-oil-in-water emulsion is an attractive new vaccine candidate that merits head-to-head comparison with other modalities of vaccine production and administration.