The structural basis of serological specificity in Shigella flexneri O-antigens

The presence of anti-LPS antibodies and human serum activity against Proteus mirabilis S/R forms in correlation with TLR4 (Thr399Ile) gene polymorphism in rheumatoid arthritis

OBJECTIVES

Proteus mirabilis strains are human pathogens responsible for urinary tract infections, which may also be involved in rheumatoid arthritis (RA).

DESIGN AND METHODS

We determined whether the binding site of anti-LPS antibodies on the O-polysaccharide part of P. mirabilis LPS correlates with the level of TLR4 (Thr399Ile) gene polymorphism in the sera of RA patients. We investigated the deposition of C3d and C5b complement components on the P. mirabilis LPS. The ELISA method used in this study was optimized with LAL test and laser interferometry.

RESULTS

Depending on LPS P. mirabilis used in these studies, the amount of antibodies in RA patients sera varied. We did not observe a correlation between anti-LPS antibodies binding and the level of TLR4 (Thr399Ile) gene polymorphism. We found that the lower complement components deposition by O49 in contrast to O9 LPS correlates with its reduced sensitivities to human complement-mediated killing.

CONCLUSION

The immunological response against P. mirabilis LPS might play a role in rheumatoid arthritis.

Optimization of virulence functions through glucosylation of Shigella LPS

Shigella, the leading cause of bacillary dysentery, uses a type III secretion system (TTSS) to inject proteins into human cells, leading to bacterial invasion and a vigorous inflammatory response. The bacterium is protected against the response by the O antigen of lipopolysaccharide (LPS) on its surface. We show that bacteriophage-encoded glucosylation of Shigella O antigen, the basis of different serotypes, shortens the LPS molecule by around half. This enhances TTSS function without compromising the protective properties of the LPS. Thus, LPS glucosylation promotes bacterial invasion and evasion of innate immunity, which may have contributed to the emergence of serotype diversity in Shigella.

Bactericidal activity of normal cord serum (NCS) against Gram-negative rods with sialic acid-containing lipopolysaccharides (LPS)

Sialic acids, that are important constituents of animal tissue glycoconjugates, are also present in antigens of some bacterial strains. Capsular polysaccharides with sialic acid have been extensively studied whereas little is known on lipopolysaccharides which contain sialic acid. The susceptibility of Gram-negative strains with sialic acid-containing lipopolysaccharides to the bactericidal action of the sera of newborns was examined. The strains investigated showed variable sensitivity to the bactericidal action of normal cord serum.