SIMPLE DETERMINATION OF POLYSACCHARIDE SPECIFIC ANTIBODIES BY MEANS OF CHEMICALLY-MODIFIED ELISA PLATES

A new ELISA technique using Nunc CovaLink NH microtiter plates has bee n developed to measure anticapsular polysaccharide specific antibodies . Capsular polysaccharide (PS) of Haemophilus influenzae type b (PRP) and pneumococcal antigens types 3, 6, 8, 14, 19, 23 were immobilized o n CovaLink NH. These are modified plates with secondary amino groups b ound to their surface which, in the presence of a water-soluble carbod iimide as coupling reagent, facilitate the direct binding of polysacch arides. We compared the binding characteristics of PS antigens to Cova Link NH and a conventional polystyrene ELISA plate. Checkerboard titra tion of PS antigens between 0.04-30 mu g/ml clearly demonstrated that with Covalink NH optimal binding of a pooled serum from immunized dono rs was achieved for all PS antigens tested at a concentration of 1 mu g/ml, while binding of PS to the conventional plate was rather poor ev en at concentrations of 30 mu g/ml. The CVs for the ELISA ranged from 1.1 to 2.8% for intra-assay comparisons and from 3.6 to 7.3% for inter -assay comparisons. In addition, when PRP-IgG antibodies were determin ed with the CovaLink NH ELISA and compared with the Farr assay an acce ptable correlation (r = 0.89, p < 0.0001) was obtained. The technique described provides a simple end sensitive tool for evaluating specific immunity to PS antigens.