THE IMMUNOGENICITY OF REASSORTANTS OF THE COLD-ADAPTED INFLUENZA-A MASTER STRAIN A ANN ARBOR/6/60 IS DETERMINED BY BOTH THE GENES FOR COLD-ADAPTATION AND THE HEMAGGLUTININ GENE/

Two surface antigen segregants were prepared by co-infection of chicke n embryo kidney cell cultures with reassortants of the cold-adapted in fluenza A master strain A/Ann Arbor/6/60-ca (H2N2) possessing the surf ace antigens of A/Queensland/6/72 (H3N2) and A/Hong Kong/123/77 (H1N1) and other genes that were common to the master strain. The segregants were shown by serological tests to possess H3N1 and H1N2 surface anti gens but it was not possible to determine the presence of H1 or N1 gen es by single-stranded RNA polyacrylamide gel electrophoresis. The immu nogenic properties of A/Queensland/6/72-ca and H3N1 segregant CR6/35/2 /9 were compared by immunising mice intranasally with graded doses of each virus twice at an interval of 3 weeks and then challenging with t he wild-type A/Queensland/6/72 (H3N2). Clearance of the challenge viru s occurred in mice immunised with the same vaccinating dose, indicatin g that the immunogenicity of both the ca H3N2 and H3N1 viruses was ide ntical and similar findings were obtained for mice immunised with A/Ho ng Kong/123/77-ca and the H1N2 segregant CR6/35/1/19 and challenged wi th the wild-type A/Hong Kong/123/77. Therefore, there appears to be a good correlation between immunogenicity and the inheritance of the hae magglutinin gene.