OBJECTIVETo explore the important role of the terminal residues containing sialic acid (SA) in Campylobacter jejuni (CJ) lipopolysaccharide (LPS) as the critical antigen to induce nerve damage, and also to identify immunopathological evidence for the hypothesis of molecular mimicry and cross-immunity between CJ LPS and gangliosides.

METHODSA mutant of Pen O:19 CJ with neuB1 gene inactivated and LPS outer core terminal residues losing SA was to be constructed. PCR and RT-PCR were used to confirm the mutant. Capability of CJ LPS binding to cholera toxin B subunit (CTB) was tested. Guinea pigs were systematically immunized with LPS of the wild and the mutant strains, respectively. Titers of anti-LPS and anti-ganglioside GM(1) IgG antibodies in sera of immunized guinea pigs were detected by ELISA. Pathological study for sciatic nerves of both Guinea pigs either immunized systematically or perineural injection with their immunized serum was finished.

RESULTS(1) The mutant of CJ O:19 strain with inactivated neuB1 gene was successfully constructed and lost transcriptional activity of neuB1 gene in the mutant strain was confirmed by PCR and RT-PCR. SA was well demonstrated by both acidic ninhydrin reaction and periodate-resorcinol reaction in the LPS of wild strain but not in the mutant LPS; (2) Compared with the titers before immunization, the titers of anti-GM(1) IgG antibody increased in sera of guinea pigs immunized with LPS of the wild strain. However there were no detectable anti-GM(1) IgG antibody in sera of the animals immunized with mutant LPS and PBS. (3) The incidence of pathological fibers of sciatic nerves in wild CJ LPS group (17.3%) was significantly higher than the mutant CJ LPS group (chi(2) = 125, P < 0.01); the difference between the mutant CJ LPS group and control group was not statistically significant (chi(2) = 1.633, P > 0.05). (4) After perineural injection with immunized serum, the incidence of pathological fibers of sciatic nerves in wild strain group (67.8%) was also significantly higher than the incidence of mutant group (P < 0.01).

CONCLUSIONA mutant of CJ O:19 strain neuB1 gene inactivated and SA component of terminal structure of LPS lost was successfully constructed. And it no longer expressed SA component which is the normal terminal structure of LPS in wild strain. The capability of the wild strain to induce increased titers of anti-GM(1) antibody and immune-mediated nerve damage was simultaneously lost for the mutant strain. It could be a strong immunopathologic evidence to identify the molecular mimicry hypothesis between CJ LPS and ganglioside epitope in nerve on the pathogenesis of CJ related GBS. The terminal residues containing SA should be as the basic GM1-like structure in CJ LPS.