infection in man is associated with chronic gastritis and peptic ulcer disease. The virulence factors of the species are still under investigation. Among these, the lipopolysaccharide (LPS) is a potential pathogenic factor of the micro-organism, whose biological activity can be estimated by immunological parameters. The aim of this study was to determine the ability of pure LPS extracted from clinical isolates of to induce mitogenicity, secretion of tumour necrosis factor-alpha (TNF-α), and spleen growth in a murine model. Rough and smooth LPS from were used as controls. The results showed that, like the control LPS, all extracts of LPS induced mitogenic activity, stimulated synthesis of TNF-α and induced spleen growth, although the effects produced by the majority of the LPS samples analysed were less intensive than those produced by the LPS. The immunological parameters analysed allowed the detection of two types of LPS: one of low biological activity and one of high biological activity. The most active LPS was extracted from strains isolated from patients with increased mucous damage associated with epithelial regeneration. Surprisingly, these strains were negative and belonged to a low virulence genotype according to gene (s1bm2 and s2m2). The results suggest the need to re-evaluate the role of the LPS as a virulence factor for some strains of .


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