One important feature of influenza A/H5N1 immunopathogenesis is the appearance of hypercytokinemia (cytokine storm) which is characterized by the extreme production and secretion of large numbers and excessive levels of pro-inflammatory cytokines. H5N1 targets specific host cells, i.e., bronchiolar cells, macrophages and type 2 alveolar pneumocytes. These cells, but not those in the tracheal or the upper path of the respiratory tract, express the α2-3 sialic acid receptors, the binding site for H5-hemagglutinin. It has been reported that H5N1 infection induced the production of TNF-α, IP-10, IL-6 and IFN-β in human alveolar and bronchial cells. Recent data, however, suggest that H5N1 can also induce cytokine release via an infection-independent mechanism. This study aimed to investigate the mechanism by which H5N1 triggers expression of cytokines/ chemokines in the respiratory epithelium. Expression of the mRNAs of interest in 16HBE14o cells treated with inactivated-H5N1 was analyzed by quantitative RT-PCR. Our results showed that the inactivated-H5N1 increased mRNA expression of IL-6 and IL-8 but not of TNF-α, RANTES and IP-10. Since cytochalasin D treatment, which disrupts actin cytoskeleton and, hence, inhibits endocytotic uptake of the virus, had no effect on the effect of the inactivated-H5N1 on cytokines mRNA expression, this effect of H5N1 did not require the presence of the virus particles in the cytosol. Cytokines production can, therefore, be initiated by an interaction between H5N1 capsule and surface membrane of the respiratory epithelial cells. The underlying mechanism by which H5N1 generates this infection-independent effect on cytokine production is currently under investigation.