Rabbit antibodies to ovine submaxillary mucin. detection, specificity and cross-reactivity

A newly developed passive hemagglutination inhibition technique was used to show that at least 2 families of antibodies are generated after immunization of rabbits with ovine submaxillary mucin (OSM)§ in homogeneous form. OSM-specific antibodies were non-precipitating in agar and liquid phase, easily detectable by a passive hemagglutination technique, and directed primarily to the carbohydrate side chain. In the case of subcutaneous immunization with OSM emulsified in complete Freund's adjuvant, the immunodominant determinants were the disaccharide prosthetic group (NAN-galNAc-protein) and a desialized moiety (galNAc-protein) which comprises about 14% of total prosthetic groups in OSM as isolated. Modest changes in the terminal sialic acid were associated with reduced interaction with anti-OSM sera. By contrast, intravenous immunization with OSM coupled to red blood cells elicited an additional family of antibodies with specificity for apo-protein. Explanations for this switch in specificity are considered.