STRUCTURAL REQUIREMENTS OF SYNTHETIC OLIGOSACCHARIDES TO BIND MONOCLONAL-ANTIBODIES AGAINST CHLAMYDIA LIPOPOLYSACCHARIDE

Monoclonal antibodies were generated against a synthetic glycoconjugat e containing the trisaccharide alpha-Kdo-(2-->8)-alpha-Kdo-(2-->4)-alp ha-Kdo (Kdo, 3-deoxy-D-manno-2-octulopyranosonic acid) which represent s the genus-specific epitope of the lipopolysaccharide from the obliga tory intracellular human pathogen Chlamydia. Antibodies of all immunog lobulin G isotypes were obtained and characterized by enzyme immunobin ding and inhibition assays using the immunizing antigen as wed as chem ically synthesized derivatives of the Kdo trisaccharide. The latter co ntained (1) one of the three residues in beta-instead of alpha-linkage , (2) a Kdo residue the carboxyl group of which had been reduced to a CH2OH group (Kdo(C1-red)), or (3) changing the linkage of the terminal Kdo from 2-->8 to 2-->4. Only one compound, namely, ha-Kdo-(2-->8)-al pha-Kdo(C1-red)-(2-->4)-alpha-Kdo exhibited binding to and inhibition of Kdo trisaccharide-specific antibodies, whereas all other compounds were not active, Structural and conformational investigations using NM R spectroscopy at high field on the allyl glycosides of the oligosacch arides 6-12 confirmed the conformational similarities between those st ructures 4, 5, and 10 which were able to bind to the antibodies invest igated.