1. 3. Results Application of IFN-  and IFN-  significantly reduced IL-6 and IL-8 expression both in CVB3 infected and mock infected myocardial fibroblasts. Moreover, MCP-1 expression was increased by high concentrations of IFN-  (1000 IU/ml). The reduction of IL-8 expression by IFN-  was concentration-dependent. For example, IL-8 concentrations were reduced to 508 pg/ml (SD 70) by 100 IU/ml IFN- , and to 109 pg/ml (SD 28) by 1000 IU/ml IFN-  (untreated controls: 1063 pg/ml (SD 299)). By contrast, IFN-  had no significant effect on IL- 6, IL-8, and MCP-1 expression. As interferons have antiproliferative activities, which are related to a general reduction of protein synthesis in many cell lines, we investigated whether the reduction of IL-8 expression by IFN-  is caused by “non-specific” antiproliferative effects. However, antiproliferative effects of IFN-  on human myocardial fibroblasts were very low (<30% with 1000 IU/ml) indicating that the suppression IL-8 expression is specific and not related to cytotoxicity. Suppression of interleukin 8 expression: an indirect antiviral activity of interferon-  and interferon- , but not interferon-  in coxsackievirus B3 infected human myocardial fibroblasts A. Heim, S. Weiss, S. Zeuke Institut für Virologie, Medizinische Hochschule Hannover, 30623 Hannover ahei@virologie.mh-hannover.de 1. Background Interferon  (IFN-  ) has a more than 120-fold higher antiviral activity than the closely related type-I interferon-  (IFN-  ) in human myocardial fibroblasts infected with coxsackievirus B3 (CVB3) [Heim et al., 1996], whereas in most cell/virus systems the antiviral activities of IFN-  and IFN-  are almost identical. Moreover, the “immune” interferon-  (IFN-  ) is also highly active against CVB3 replication in human myocardial fibroblasts. CVB3 replication induces interleukin 6 (IL-6) and interleukin 8 (IL-8) expression in cultures of human myocardial fibroblasts [Heim et al. 2000], and suppresses the expression of monocyte chemoattractant protein-1 (MCP-1). As IL-8 stimulates enterovirus replication [Khabar et al., 1997], we investigated whether the higher antiviral activity of IFN-  (and IFN-  compared to IFN-  may be caused by autocrine “immunomodulating” effects, e.g. a suppression of IL-8 expression by IFN-  and IFN- . 2. Material and Methods Human myocardial fibroblasts were treated for 9 days with either IFN- , IFN-  or IFN-  (0, 10, 100, and 1000 IU/ml), and concentrations of IL-6, IL-8 and MCP-1 were measured in culture supernatants by enzyme-linked immunoassays. In addition, IL-8 mRNA concentrations were determined by quantitative reverse transcription/ polymerase chain reaction (qPCR) using competitive internal standards (IS). All samples were diluted to equal concentrations of a house- keeping gene (GAPDH) before performing IL-6 and IL-8 qPCR. In order to evaluate the antiviral effects of a reduction of “autocrine” IL-8, CVB3 infected myocardial fibroblasts were treated with a monoclonal antibody (MAB) neutralizing IL-8, and virus yields were quantified by plaque-assays. Furthermore, antiproliferative effects of the three interferons were evaluated by EZ4U staining Moreover, IFN-  reduced IL-8 mRNA concen- trations in human myocardial fibroblasts. As all samples were prediluted to equal concentrations of GAPDH (a "house-keeping gene") mRNA, a specific reduction of IL-8 mRNA can be concluded. CVB3 infected human myocardial fibroblasts were incubated with an IL-8 neutralizing monoclonal antibody to determine the contribution of IL-8 reduction to the high antiviral activity of IFN-  and IFN-  eutralization of IL-8 resulted in a significant, but minor antiviral effect compared to the antiviral effects of IFN-  and IFN-  4. Conclusions In contrast to IFN- , IFN-  has ”immuno- modulating” properties (e.g. IL-8 suppression) similar to the type II interferon (IFN-  ) in human myocardial fibroblasts. These activities contribute to the high antienteroviral activity of IFN- , and may be useful in the treatment of enteroviral heart disease. However, the reduction of IL-8 expression is not sufficient to explain the 120-fold higher antiviral activity of IFN-  compared to IFN- . Recently discovered differences in the activation of JAK-1 kinase by IFN-  and IFN-  may also contribute to the high antiviral activity of IFN-  [Grumbach 1999]. 5. 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