During infection, the functional status of the innate immune system is tightly regulated. Although signals resulting in activation have been well characterized, counterregulative mechanisms are poorly understood. Suppressor of cytokine signaling (SOCS) proteins have been characterized as cytokine-inducible negative regulators of Janus kinase/STAT signaling in cells of hemopoietic origin. To analyze whether SOCS proteins could also be induced by pathogen-derived stimuli, we investigated the induction of SOCS-1 and SOCS-3 after triggering of macrophage cell lines, bone marrow-derived dendritic cells, and peritoneal macrophages with CpG-DNA. In this study, we show that CpG-DNA, but not GpC-DNA, induces expression of mRNA for SOCS-1 and SOCS-3 in vitro and in vivo. SOCS mRNA expression could be blocked by chloroquine and was independent of protein synthesis. Inhibitors of the mitogen-activated protein kinase pathway triggered by CpG-DNA were able to impede induction of SOCS mRNA. CpG-DNA triggered synthesis of SOCS proteins that could be detected by Western blotting. SOCS proteins were functional because they inhibited IFN-γ as well as IL-6- and GM-CSF-induced phosphorylation of STAT proteins. Furthermore, IFN-γ-induced up-regulation of MHC class II molecules was also prevented. The same effects could be achieved by overexpression of SOCS-1. Hence, the results indicate a substantial cross-talk between signal pathways within cells. They provide evidence for regulative mechanisms of Janus kinase/STAT signaling after triggering Toll-like receptor signal pathways.

Staphylococcus aureus is one of the most significant pathogens causing nosocomial and community-acquired infections. Among the secreted staphylococcal virulence factors, there is a growing list of enterotoxins which can induce gastroenteric syndrome and toxic shock syndrome. Here, we developed a real-time fluorescence PCR assay (TaqMan PCR) for the detection of genes encoding staphylococcal enterotoxins A, B, C1, and D (SEA, SEB, SEC1, and SED) of S. aureus as well as the mecA gene encoding methicillin resistance and the femB gene as a specific genomic marker for S. aureus. SEA to SED were selected because they are the four classically described enterotoxins of S. aureus and because they were detected by latex agglutination. In order to evaluate the reliability of TaqMan PCR, we investigated 93 isolates of S. aureus derived from patients at our hospital over 5 months and compared the results with data obtained by a commerciall available reversed passive latex agglutination assay (SET-RPLA) for these isolates. Thirteen enterotoxin genes were detected by TaqMan PCR; however, no proteins expressed by these genes were detected by SET-RPLA. As a result, more isolates of S. aureus (n ‫؍‬ 44) were found positive by TaqMan PCR for one or more enterotoxin genes than by SET-RPLA for the respective proteins expressed by these genes (n ‫؍‬ 40). We conclude that TaqMan PCR is more sensitive because it offers the possibility for determining enterotoxins on a genotypic basis. Additionally, the assay allows the parallel detection of genes for SEA to SED and methicillin resistance in S. aureus. Furthermore, real-time PCR is well suited for screening large numbers of samples at the same time, allowing rapid, reliable, efficient, and cost-saving routine laboratory diagnosis.

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