Original antigenic sin to influenza in rats.

The presumed influenza anamnesis of the human population born before 1956—the year when A(H1NI) influenza viruses came out of circulation—is modelled on sixty male white rats. The model is an essay to clarify why these people demonstrated higher resistance to influenza A(H1N1) during its recurrence in late 1977, compared with young individuals, who obviously contacted this subtype for the first time. The dynamics of anti-influenza antibody formation (assessed by the indirect haemagglutination test, IHT) against different A subtypes used for reimmunizations reflected the status of immunological memory (IM) of the animals. Both humoral and secretory immune systems of the rats showed long lasting IM to influenza A(H1N1) antigens. However, the characteristics of the original antigenic sin (OAS) were manifested only by the humoral immune system. The antibodies against the original A(H1N1) viruses in the group, that received consecutive immunizations with A(H2N2) and A(H3N2) viruses, remained constantly higher than the same antibodies in the group intact to other subtypes, except to A(H1N1). This is an indication, that the OAS might serve as a natural mechanism for the maintenance of a sufficiently high concentration of antibodies, that could provide a secure protection at the time of return of the corresponding influenza viruses. In this respect, two types of manifestations of IM are discussed.