Expression of Cytokine and Chemokine Genes by Human Middle Ear Epithelial Cells Induced by Influenza A Virus andStreptococcus pneumoniaeOpacity Variants

Abstract

Real-time PCR and enzyme-linked immunosorbent assay were used to evaluate the ability of influenza A virus and Streptococcus pneumoniae opacity variants, either alone or in combination, to induce cytokine and chemokine genes in primary cultures of human middle ear epithelial (HMEE) cells. Following treatment with influenza A virus, the induction of gene expression, which occurred in a dose-and time-dependent manner, was strong for macrophage inflammatory protein 1␣ (MIP-1␣) and MIP-1␤; moderate for tumor necrosis factor alpha (TNF-␣), interleukin-6 (IL-6), and IL-8; and weak for IL-1␤ and monocyte chemotactic peptide 1 (MCP-1). Except for TNF-␣, all the gene products were detected in the cell culture supernatants. In contrast, infection of HMEE cells with S. pneumoniae alone induced low levels of mRNA expression of MIP-1␣ and MIP-1␤ and did not significantly induce the transcription of the other cytokines and chemokines examined. However, both S. pneumoniae opacity variants increased mRNA expression of MIP-1␣, MIP-1␤, IL-6, and MCP-1 in HMEE cells activated by a prior influenza A virus infection compared to levels in cells treated with either agent alone. Up-regulation of IL-6, IL-8, and MCP-1 mRNA expression and production by the virus in combination with opaque S. pneumoniae was two-to threefold higher than that induced by the virus combined with the transparent S. pneumoniae variant. These data indicate that the activation of HMEE cells by influenza A virus enhances the induction of cytokine and chemokine gene transcripts by S. pneumoniae and that this effect appears to be most pronounced when S. pneumoniae is in the opaque phase.Streptococcus pneumoniae is the primary bacterial pathogen associated with otitis media (OM), accounting for 30% of the cases of this disease (5). The process whereby S. pneumoniae becomes established in the human nasopharynx and effects the transition from a colonized to a disease state in the middle ear has been the focus of intense investigation for years. S. pneumoniae-induced OM is characterized by the presence of numerous bacteria, inflammatory cells, middle ear effusion, and middle ear epithelial cell injury. It is widely accepted that the middle ear epithelium plays a crucial role, serving as a first line of defense in the interaction with invasive pathogens during OM (25). Innate proinflammatory responses induced in host cells by S. pneumoniae infection that may contribute to the OM pathology include the synthesis and release of cytokines, chemokines, and other inflammatory mediators. Extensive evidence suggests that the middle ear epithelium not only is a physical barrier but also has the potential to synthesize a variety of cytokines, including interleukin-1 (IL-1), IL-6, IL-8, and IL-10, which are recognized as being important local mediators in acute inflammation in various animal models of OM (20,28,33). Activation of host epithelial and endothelial cells by cytokines results in a shift in S. pneumoniae adherence to new receptors, particularly the platelet-activating fa...

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