Antigenic glycopolypeptides HA1 and HA2 of influenza virus haemagglutinin. IV. Immunogenic properties of separated haemagglutinin glycopolypeptides.

Highly purified haemagglutinin glycopolypeptides HA1 and HA2 were effective in eliciting an antibody response. HA2 had a markedly greater immunogenic potential than HA1. In gel double immunodiffusion, sera from rabbits immunized with HA2 produced more distinct precipitin lines than sera obtained by immunization with HA1. Both kinds of rabbit sera gave precipitation with homologous antigen and with bromelain-released and purified haemagglutinin (B-HA). In radioimmunoassay, sera from rabbits immunized with HA2 revealed considerable titres for 125I-labelled HA2 binding and reacted preferentially with 125I-labelled HA2. In general, sera from rabbits immunized with HA1 exhibited low titres for 125I-labelled HA1 binding: usually they reacted also with 125I-labelled B-HA and 125I-labelled HA2. Only rabbits injected with a few doses of HA1 at short intervals revealed preferential binding for 125I-labelled HA1. Glycopolypeptides HA1 and HA2 failed to induce haemagglutination-inhibiting and virus neutralizing antibodies in rabbits.