Structural Studies of Shigella flexneri O‐Antigens

The structures of the O‐antigens of all known serotypes and subserotypes of Shigella flexneri have been reinvestigated. The results support the assumption that these antigens are composed of a basic tetrasaccharide repeating unit (1), to which α‐D‐glucopyranosyl and/or O‐acetyl groups are attached at different positions. The immunological determinants responsible for O‐factors I, II, IV, V and 7,8 contain α‐D‐glucopyranosyl groups, the locations of which have been determined. O‐Factor 6 is due to O‐acetyl groups, linked to O‐2 of the 3‐substituted α‐L‐rhamnopyranosyl residue in unit 1 and O‐factor III seems to be due to the same groups. The chemical natures of the determinants responsible for O‐factors 4 and 3, 4 are still obscure. The structural studies indicate that the immunological classification of Sh. flexneri serotypes and subserotypes, as regards these O‐factors, may need revision.