Comparative analysis of two meningococcal immunotyping monoclonal antibodies by resonant mirror biosensor and antibody gene sequencing

Lipooligosaccharide (LOS) is a major surface component of the cell walls of Neisseria meningitidis, which is important for its roles in pathogenesis a nd antigenic variation, as a target for immunological typing, and as a poss ible vaccine component. Although the structures of many antigenic variants have been determined, routine immunological typing of these molecules remai ns problematic. Resonant mirror analysis was combined with gene sequencing to characterize two monoclonal antibodies (MAbs) used in typing panels that were raised against the same LOS immunotype, 13,7,9. The two MAbs (MAb 4A8 -B2 and MAb 9-2-L379) were of the same immunoglobulin subtype, but while MA b 9-2-L379 was more than a 1,000-fold more sensitive in immunotyping assays of both whole meningococcal cells and purified LOS, MAb 4A8-B2 was more sp ecific for immunotype L3,7,9. The differences in sensitivity were a consequ ence of MAb 9-2-L379 having a 44-fold-faster association constant than MAb 4A8-B2. Comparison of the amino acid sequences of the variable chains of th e MAbs revealed that they had very similar heavy chains (81% amino acid seq uence identity) but diverse light chains (54% sequence identity). The diffe rential binding kinetics and specificities observed with these MAbs were pr obably due to differences In the epitopes recognized, and these were probab ly a consequence of the different immunization protocols used in their prod uction.