IL-8 release from human neutrophils by the respiratory syncytial virus is independent of viral replication.

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Elevated interleukin-8 levels and a massive accumulation of neutrophils (PMN) are the hallmark of a variety of severe lung diseases. The respiratory syncytial virus (RSV), an important respiratory pathogen, induces interleukin-8 (IL-8) release from human PMN, however, the mechanism is as yet unknown. We analyzed the role of virus uptake, intracellular virus replication, virus attachment, and of virus capsid proteins for the induction of IL-8 (protein + mRNA) in human PMN. Cell supernatants were analyzed for IL-8 release via enzyme-linked immunosorbent assay; cell pellets were analyzed for IL-8-specific mRNA expression and for RSV-specific genomic and RSV-specific mRNA by reverse transcriptase-polymerase chain reaction. Stimulation of human PMN with viable, heat-inactivated, or UV-inactivated RSV [at a multiplicity of infection (m.o.i.) from 0.01 up to 10] induced IL-8 production (protein + mRNA) to a similar degree. Maximal IL-8 release was observed at a m.o.i. of 5-10 after 18-24 h. RSV-specific genomic RNA was present inside PMN up to 24 h independent of whether viable or inactivated RSV was used. Withdrawal of extracellular viable or inactivated (heat, UV) RSV after infection of PMN (2 h) abolished IL-8 mRNA expression and IL-8 release; the intracellular persistence of RSV lasted for up to 24 h. Stimulation of human PMN with purified RSV G-protein, a major capsid protein, in a concentration range from 0.1 up to 2.5 microg/5 X 10(5) PMN resulted in an increased IL-8 release from human PMN but to a significantly lesser degree compared with the intact RSV. RSV G-protein concentration above 1 microg inhibited the RSV-induced IL-8 release by up to 90%. Our data contribute to the understanding of the pathomechanisms leading to IL-8 release from human PMN.