STRUCTURALLY DEFINED EPITOPES OF HAEMOPHILUS-DUCREYI LIPOOLIGOSACCHARIDES RECOGNIZED BY MONOCLONAL-ANTIBODIES

By use of enzyme-linked immunosorbent assay and immunoblotting techniq ues, the migration patterns and binding epitopes of lipooligosaccharid es (LOS) from 10 Haemophilus ducreyi strains were investigated with tw o monoclonal antibodies (MAbs), MAHD6 and MAHD7, raised against LOS fr om H. ducreyi ITM 2665, Closely related LOS, with defined structures, from Haemophilus influenzae, Bordetella pertussis, Aeromonas spp,, and synthetic glycoproteins were also included in the analyses, The MAbs bound to conserved epitopes of LOS exposed on the surface of H. ducrey i. The MAb MAHD6 reacted with 8 of the 10 LOS from H. ducreyi but,vith none of the other Haemophilus or Bordetella spp, with structurally de fined LOS. It is suggested that MAb MAHD6 binds to a LOS epitope (-DD- Hepp-1-->beta-D-Glcp-). This LOS epitope is not present in the hexasac charide structure of LOS from H. ducreyi ITM 4747 (E. K. H. Schweda, A . C. Sundstrom, L. M. Eriksson, J. A. Jonasson, and A. A. Lindberg, J. Biol. Chem. 269:12040-12048, 1994). Because MAb MAHD6 reacts with the epitope mentioned above, it also discriminates between the two LOS st ructures, the hexasaccharide group and the nonasaccharide group, of H. ducreyi strains, MAb MAHD7 recognizes the common conserved inner core region of the LOS because it reacts with all H. ducreyi strains and w ith LOS with minor components in the inner core epitope structure, Rab bit polyclonal sera raised against the LOS from strains CCUG 4438 and CCUG 7470 were tested with the 10 LOS from the H. ducreyi strains. The antiserum to CCUG 7470 reacted with all H. ducreyi strains as did MAb MAHD7, whereas the antiserum to CCUG 4438 reacted with only its homol ogous strain and strain ITM 4747. Also, the LOSs of our reference stra ins CCUG 4438 and CCUG 7470 were structurally analysed by use of sugar analyses and electrospray ionization-mass spectrometry. The hexasacch aride and nonasaccharide structures obtained from LOS of strains CCUG 4438 and CCUG 7470 were identical to the described LOS structures from H. ducreyi ITM 4747 and ITM 2665, respectively, In conclusion, the MA b MAHD6 recognizes an epitope present in the nonasaccharide LOS group, whereas the MAb MAHD7 recognizes a conserved epitope on LOS of H. duc reyi, which is present in all strains of H. ducreyi tested. Two major groups of oligosaccharides were distinguished by their LOS structures and the reactivity of monoclonal as well as polyclonal antibodies. The majority of H. ducreyi strains possess a nonasaccharide structure of LOS.