FIG. 1.

Binding to solid-phase adipic dihydrazide derivative of OAc-positive polysaccharide, which is known to express both OAc-positive and OAc-negative epitopes. Sera were tested in the presence of a 10-μg/ml concentration of soluble OAc-positive (gray bars) or OAc-negative (striped bars) meningococcal group C polysaccharide or, as a negative control, group Y polysaccharide (open bars) (solid bars, no polysaccharide). The control MAb 706 is known to recognize an epitope on OAc-negative polysaccharide, but its binding is inhibited by both OAc-negative and -positive group C polysaccharides because of nonstoichiometric OAc. MAb 735 preferentially binds OAc-positive polysaccharide. The inhibition observed in the ELISA is consistent with this binding specificity. Human serum 2C from an adult immunized with the Baxter group C conjugate vaccine prepared from OAc-negative polysaccharide is completely inhibited by OAc-negative polysaccharide.