Early RNA synthesis in influenza virus-infected cells

Biological activities of 'noninfectious' influenza A virus particles

Only a small fraction of influenza A virus (IAV) particles within a viral population register as infectious by traditional infectivity assays. Despite constituting the most abundant product of influenza infection, the role that the 'noninfectious' particle fraction plays in the biology of the virus has largely been ignored. This review shines a light on this oft-ignored population by highlighting studies, both old and new, that describe the unique biological activities of these particles, and discussing what this population can tell us about the biology of IAV evolution and disease.

Biological characteristics of a cold-adapted influenza A virus mutation residing on a polymerase gene

The biological function of a cold-adapted (ca) mutation residing on the PB2 gene of an influenza A/Ann Arbor/6/60 (A/AA/6/60) ca variant virus in the viral replication cycle at 25 degrees C was studied. The viral polypeptide synthesis of A/AA/6/60 ca variant at 25 degrees C was evident approximately 6 hours earlier than the wild type (wt) virus and yielded twice as many products. The quantitative analysis of viral complementary RNA (cRNA), synthesized in the presence of cycloheximide, revealed that A/AA/6/60 ca variant and a single gene reassortant that contains only the PB2 gene of the ca variant with remaining genes of the wt virus produced equal amount of cRNA at 25 degrees and 33 degrees C, which was an amount approximately four fold greater than the wt virus' cRNA synthesized at 25 degrees C. These results strongly suggest that the ca mutation residing on the PB2 gene of A/AA/6/60 ca variant affects the messenger RNA synthesis at 25 degrees C in the primary transcription.

Mechanism of host defense suppression induced by viral infection: mode of action of inosiplex as an antiviral agent

The mechanism of influenza virus (INFV)-induced immunosuppression and the mode of inosiplex action against INFV infection were studied. INFV suppressed both anti-lipopolysaccharide and anti-sheep erythrocyte antibody production in mice. INFV infection caused viral mRNA synthesis and increased total RNA synthesis in lymphocytes, but total mRNA synthesis was decreased. The translational ability of INFV-infected lymphocytes was also suppressed. Thus, INFV seemed to cause suppression of both mRNA synthesis and the translational ability of lymphocytes, resulting in suppression of lymphocyte functions. Inosiplex potentiated antibody production against sheep erythrocytes but not against lipopolysaccharide in normal and INFV-infected mice. Adamantanamine did not produce such a potentiating effect. The lymphocytes obtained from INFV-immunized and inosiplex-treated mice conferred resistance against INFV infection. This resistance was partially inhibited by anti-Thy 1.2 antibody treatment of the lymphocytes. In an adoptive cell transfer system, inosiplex treatment of T-cell donors potentiated antibody production when a non-immunosuppressive carrier (human serum albumin) was used. When an immunosuppressive carrier (INFV) was used, inosiplex treatment of either B-cell donors or T-cell donors increased antibody production. Direct introduction of inosiplex into lymphocytes by a cell fusion technique stimulated anti-sheep erythrocyte antibody production more effectively than the addition of inosiplex to cultures. Inosiplex increased total RNA and total mRNA syntheses in phytohemagglutinin-treated lymphocytes. In INFV-infected lymphocytes, inosiplex decreased syntheses of total RNA, total mRNA, and viral mRNA and restored translational ability. From these results, we concluded that inosiplex penetrates into lymphocytes and suppresses viral RNA synthesis and that it supports lymphocyte functions by promoting RNA synthesis and translational ability, both of which are necessary for hosts.