Ability of temperature-sensitive mutants of the recombinant influenza S/N (H2N1) virus to induce immunity to parental (H0N1 and H2N2) viruses.

The behavior in mice of two thermosensitive (ts) mutants (denoted ts217 and ts700) of the recombinant influenza virus S/N (H2N1) was studied. The parental thermoresistant (tr) virus and both of the mutants were capable of inducing protection against pneumotropic A/Singapore (H2N2) and A/WS (H0N1) challenge viruses. Immunity against the Singapore virus, with which the S/N virus shared the hemagglutinin, developed earlier than against the WS virus, with which the S/N virus shared the neuraminidase. The tr and ts217 viruses were immunologically more active than the ts700 virus. The first two viruses grew markedly better in mouse lungs than did the latter. In the course of ts217 virus replication in vivo, revertants capable of growing at 39 degrees C appeared readily. On the other hand, the ts700 virus proved to be genetically stable. These data seem to provide evidence of a linkage between the stability of the ts phenotype, reproductive capacity in mouse lungs, and immunogenicity in the viruses examined.