Antigenic glycopolypeptides HA1 and HA2 of influenza virus haemagglutinin. II. Reactivity with rabbit sera against intact virus and purified undissociated haemagglutinin.

Rabbit sera produced against either intact virus or purified undissociated haemagglutinin were examined for reactivity with highly purified haemagglutinin glycopolypeptides. Sensitive radioimmunoassay for 125I-labelled glycopolypeptides revealed antibody reactive with either glycopolypeptide HA1, or glycopolypeptide HA2. Antibodies against the carbohydrate moiety were responsible only for a part of the binding activity. Under the conditions employed, the binding activity for glycopolypeptide HA2 was much stronger than for glycopolypeptide HA1. Competition assays suggested that immune reactivities were due to distinct antibody populations (i.e. with a specifity for glycopolypeptide HA1 and glycopolypeptide HA2, respectively). The immune reactivity to both haemagglutinin constituents, glycopolypeptides HA1 and HA2, was also shown by gel double diffusion. The precipitin line(s) corresponding to glycopolypeptide HA1 was (were) usually more distinct than precipitin line(s) corresponding to glycopolypeptide HA2. The glycopolypeptides HA1 and HA2 showed the reaction of nonidentity in immunodiffusion analysis.