engleski

The role of immune system in the control of pandemic influenza infection

The failure in the protective role of the immune system in influenza infection could take place in humans who had no previous humoral and/or cellular immunity to the virus. The severity in clinical presentation could then depend on the capacity of influenza virus to circumvent or even to inhibit different immune mechanisms necessary for successful virus elimination. Mechanisms of innate immunity (interferon, proinflammatory cytokines, chemokines, cells belonging to the innate immunity) present the first line of defense in influenza infection. Infection or vaccination induces adequate humoral immunity to different components of influenza virus: antibodies to hemagglutinin inhibit viral infection while antibodies to neuraminidase inhibit viral spread. In addition to the humoral immunity, T-lymphocytes have very important role in the influenza infection. HLA-I-restricted CD8+ cytotoxic T cells specific for nucleoprotein and matrix antigens of influenza virus are present in the lung of infected individuals and their number correlates with the virus elimination, recovery from the infection as well as the lack of secondary complications. Cellular cytotoxic immunity is often cross-reactive amongst different influenza virus subtypes due to the similarity in their antigens. Helper CD4+ T cells are important for augmentation of humoral and cytotoxic immunity, however, they are considered less important than CD8+ T cells. Current knowledge on immunity to possible pandemic influenza viruses such as H5N1 showed that the immune system in infected individuals is inappropriately activated since they have excessive cytokine secretion (so called cytokine storm), lymphopenia, disturbed CD4/CD8 ratio, and hemophagocytosis. The observed changes in early immune response to pandemic influenza virus could therefore result in lethal outcome due to both lack of pre-existing immunity and time necessary for the development of specific immunity mediated by antibodies and T lymphocytes.

influenza; pandemic; innate immunity; adaptive immunity; vaccine

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