text: Discussion
  Animal models of sepsis and myocardial injury suggest that a beta-1-->3-D-glucan like GP mediates its protective mechanisms, in part, via a rapid shift from NFkappaB- to PI3K-signaling [22,37]. Our study provides novel evidence that downstream of recognition and signaling pro-inflammatory transcription factor binding and cytokine expression of human leukocytes is switched to an anti-inflammatory phenotype by GP. 
  We confirmed and extended previous results [13-16] indicating that, in the absence of other stimuli, beta-1-->3-D-glucans induced binding of NFkappaB-, NFIL-6- and NFAT-mers to cytokine promoters. Because of the multiple band shifts observed for NFAT binding (Fig. 1A), one could speculate that there is activation of several different NFAT isoforms, probably derived from alternative splicing [38]. Interestingly, the GP-induced transcription factor binding transformed only into a very limited cytokine response, namely IL-8 and IL-1RA (Fig. 3B). Hence, our data are in aggreement with the few reports describing a beta-1-->3-D-glucan-mediated IL-8 [6,16,19] and IL-1RA production [17]. In addition, our EMSA/supershift and immunoblotting results demonstrated a GP-mediated predominant binding of NFkappaB p65 and to a lesser extent of p50 to a kappaB consensus site of the IL-8 promoter (Figs. 1A, 2). Results by Schulte and colleagues [28] pointed to an induction of IL-8 transcription depending on activation via an NFkappaB p65/65 homodimer, rather than via p65/50 heterodimers, which might be the case for the GP-mediated IL-8 transcription. A GP-mediated IL-8 transcription based upon a cooperation between transactivated NFkappaB p65 and NFIL-6 [13,39] or NFATc2 dimer binding to the IL-8kappaB site [38] seems also possible. The IL-8kappaB consensus site exhibits a preferentially p65 binding half site and thus differs from the kappaB half site described for TNFalpha and IL-1beta [27,40], supporting the idea of regulating NFkappaB binding through combinatorial associations of the subunits and the specific sequence of the decameric kappaB motif [41,42]. Unlike LPS or TSST-1, we found that GP did not induce IL-1beta, but it strongly induced IL-1RA, suggesting an immediate anti-inflammatory potential of GP. Analysing the IL-1RA promoter [34], we discovered four new binding sites (Fig. 8): an NFkappaB3 site (between -100 and -130), an NFkappaB consensus site (-266 and -280), another NFkappaB2/3 site (-288 and -302) and a more distal NFATP2/3 site (-471 and -490). Our data indicated that GP leads to production of IL-1RA primarily via induction of NFATP2/3 and NFIL-6 DNA binding, which might be due to differences in the binding motif or the composition of the activated transcription factors (NFAT) between the IFNgamma, IL-6 and IL-1RA promoter. The differential decrease of NFkappaB, NFAT and NFIL-6 binding to sites in the IL-1RA promoter as well as of IL-1RA mRNA and protein induced by selective inhibitors prior to GP treatment might suggest that these steps are linked to each other and necessary for induction of IL-1RA (Fig. 7). Regarding cellular sources, both, monocytes as well as neutrophils have been reported to produce IL-1RA [32]. Flow cytometric experiments seemed to confirm that monocytes and neutrophils were able to produce IL-8 just as IL-1RA in response to GP (data not shown). This GP-induced cytokine profile was substantially more restricted than that of LPS or TSST-1, which is likely due to differences in recognition and signaling between LPS, TSST-1 and GP. Recognition of LPS is mainly mediated through Toll-like receptor 4 and subsequent signaling via the NFkappaB pathway, leading to expression of pro-inflammatory mediators like TNFalpha [43]. A bacterial superantigen like TSST-1 acts through binding to MHC-II molecules and subsequently the T cell receptor, leading to release of mainly IFNgamma and TNFalpha, the latter via both, PI3K and p38 mitogen-activated kinase signaling [44,45]. Altogether, the induction of the neutrophil-attracting IL-8 and the anti-inflammatory IL-1RA by fungal carbohydrates (GP) may well fit to a benign PAMP response, mounting defensive mechanisms against a possible microbial attack. 
  Potentially even more relevant than the specific cytokine panel induced by GP, we found that, in the presence of other stimuli (LPS or TSST-1), GP ameliorated their pro-inflammatory immune reactions, similar to the effects in murine models of sepsis and inflammation [21-24]. Mainly, GP altered the TSST-1-induced IL-1beta/IL-1RA ratio from a pro- to an anti-inflammatory profile via down-regulation of IL-1beta and IL-6, at the same time there was a synergistic up-regulation of IL-1RA. In part, this change may be caused by GP-mediated modulations of the TSST-1 induced binding of NFkappaB, NFIL-6 and NFAT to known and up to now unknown sites within the IL-8 and IL-1RA promoter instead of the TNFalpha, IL-1beta, IL-6 or IFNgamma promoter. Accordingly, we found that the TSST-1-induced binding of NFkappaB to sites from the TNFalpha promoter negatively correlated with the GP-mediated enhancement of the TSST-1-induced IL-1RA production (r = -0.88; p < 0.01; data not shown in detail). Of the four examined NFkappaB sites from the IL-1RA promoter, mostly the TSST-1- and LPS-induced binding to the NFkappaB3 and the TSST-1-induced binding to the new NFkappaB consensus site seemed to be increased by GP. So, while we observed a GP-mediated down-regulation of the LPS- and the TSST-1-induced NFkappaB binding to sites of the TNFalpha promoter, there was an up-regulation to NFkappaB3 and NFkappaB consensus sites of the IL-1RA promoter. These seemingly contradictory data could be explained by differences in either NFkappaB subunits or conserved nucleotides (#1, 2, 3, 10) within the decameric NFkappaB binding motif between the TNFalpha and the IL-1RA promoter (for NFkappaB3 the IL-1RA motif contains a T on position 10 instead of the conserved C in the TNFalpha motif, see Table 1), probably leading to differences in binding [41,42]. Despite the location of the new NFkappaB consensus site (-266 and -280) in the inhibitory element (-250 and -294) of the IL-1RA promoter [30], we observed no inhibition. On the other side, we found an inhibitory NFkappaB2/3 site (-288 and -302) towards the end of the inhibitory element, demonstrating down-regulations of the LPS- and TSST-1-induced binding, which could not be altered by GP. In our opinion, this site may therefore represent at least a part of the previoulsy described inhibitory element [30]. The GP-modulated increase in TSST-1-induced binding to the new NFkappaB3 and NFkappaB consensus site, the NFIL-6 site [32] as well as to the novel NFATP2/3 site may explain the synergistic up-regulation of the TSST-1-induced IL-1RA production. We think that this GP-modulated activation of transcription was reflected by the decrease of the IL-1beta/IL-1RA ratio following GP + TSST-1 (Fig. 6). In this context, it has been postulated that in vitro a 100fold excess of IL-1RA over IL-1beta might control the biological effects of IL-1 [46,47]. Since, in fact, the IL-1beta/IL-1RA ratio following GP + TSST-1 is partially less than 0.01, it is not unreasonable to assume that IL-1beta bioactivity is inactivated in our system. Indeed, GP reduced the TSST-1-induced, IL-1-dependent IL-2 production of murine EL-4 cells (data not shown in detail). 
  The weaker modulating effects of GP on the LPS-induced immune response observed in this study, may be attributed to delicately balanced differences in signaling pathways between LPS and TSST-1 [43-45]. TSST-1 has been shown to use the PI3K pathway for signaling [44] and this effect may be sustained by GP treatment [22,37]. It has been demonstrated that in septic/LPS-adapted leukocytes the PI3K pathway selectively controls sIL-1RA but not IL-1beta production [48]. Signaling via PI3K has been reported to be involved in the activation of NFAT in T cells [49]. Activation of NFkappaB can also take place via PI3K [50], which may offer an explanation for a difference in signaling between GP (PI3K) and LPS (mitogen-activated kinase signaling). This idea may be supported by another study showing that despite the use of similar PRR, LPS and peptidoglycan activated the IL-1RA gene through different mechanisms/DNA-binding proteins and acted synergistically in combination, suggestive of signals which are not equivalent in all parts [51]. 
  