NATURAL AND IN-VITRO SELECTED ANTIGENIC VARIANTS OF INFLUENZA-A VIRUS(H2N2)

We provide data on the prevalence of SRH antibody to influenza A/Singa pore/1/57 (H2N2). Approximately 10.3% of sera had antibody to the infl uenza A (H2N2) subtype virus in comparison to the 36.9% of positive se ra to a representative influenza A (H3N2) and 31.5% to influenza A (H1 N1) viruses. The percentage of subjects with antibody constantly decre ased from the older to the younger age groups. Persons born after 1968 were essentially seronegative, whereas subjects born before 1900, and in the decade 1950-1959, showed the highest antibody levels to influe nza A (H2N2) viruses. These age groups also appeared to have 'protecti ve' levels of anti-HA antibody to influenza A (H2N2) virus. An antigen ic variant of A/Singapore/1/57 virus was selected in the laboratory us ing a monoclonal antibody to HA. Serological comparison of the new in vitro variant with the parental virus and two naturally occurring viru ses, namely A/England/12/64 and Tokyo/3/67, showed that certain human sera were able to distinguish the variant, indicating a restricted ant ibody repertoire in these adult and children's sera, providing an expl anation of how such variants could actually arise in nature.