Eight monoclonal antibodies (MAbs) were prepared against the lipooligo- saccharide (LOS) of group A N. meningitidis strain A1. Two of them reacted with A1 LOS without binding to 12 known LOS antigens by ELISA and dot blot assay. Immuno-blot assay and ELISA inhibition further proved that the two MAbs were specific for the A1 LOS. These results suggest that strain A1 expresses an as yet untyped LOS epitope. Other MAbs bound to some or many of the 12 LOS types.
