It is characteristic for virus infections that monocytes/macrophages and lymphocytes infiltrate infected tissue while neutrophils are absent. To understand the mechanisms selectively attracting mononuclear cells in viral diseases, we examined in an influenza A virus model the expression and regulation of chemokines as candidate molecules responsible for the immigration of leukocytes into inflamed tissue. After influenza A virus infection of human monocytes, a rapid expression of the mononuclear cell attracting CC-chemokine genes MIP-1, MCP-1, and RANTES occurred which was followed by the release of chemokine proteins. In striking contrast to CC-chemokines, the expression of the prototype neutrophil CXC-chemoattractants IL-8 and GRO-alpha was completely suppressed after influenza A infection. The release of other neutrophil chemotactic factors was excluded by microchemotaxis assays. These results suggest that the virus-specific induction of mononuclear cell-attracting chemokines accounts for the preferential influx of mononuclear leukocytes into virus-infected tissue.

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