Table 3. Brain extracellular/arterial plasma ratios.
| Cytokine | In vitro relative recovery (%) | Calculated relative recovery (%) | Median [brain extracellular]/[arterial plasma] ratio | Median [microdialysate]/[arterial plasma] ratio |
|---|---|---|---|---|
| EGF | 55.9 | 0.69*** | 0.38 | |
| Eotaxin | 54.1 | 0.39*** | 0.21 | |
| FGF2 | 46.5 | 1.29*** | 0.60 | |
| Flt3 lig | 46.2 | 1.91 | 0.88 | |
| Fractalkine | 54.0 | 1.77*** | 0.96 | |
| G-CSF | 45.2 | 3.61*** | 1.63 | |
| GM-CSF | 48.7 | 0.21*** | 0.10 | |
| GRO | 54.6 | 0.50*** | 0.27 | |
| IFNα2 | 44.8 | 0.83** | 0.37 | |
| IFNγ | 46.9 | 0.63* | 0.30 | |
| IL1α | 48.0 | 3.87*** | 1.86 | |
| IL1β | 38.4 | 2.01** | 0.77 | |
| IL1ra | 38.4 | 3.55*** | 1.36 | |
| IL2 | 52.8 | 0.35*** | 0.19 | |
| IL3 | 28.6 | 5.64*** | 2.73 | |
| IL4 | 56.7 | 1.06** | 0.60 | |
| IL5 | 39.0 | 8.26 | 3.22 | |
| IL6 | 25.5 | 35.75*** | 9.12 | |
| IL7 | 46.3 | 1.91** | 0.89 | |
| IL8 | 73.4 | 20.30*** | 14.90 | |
| IL9 | 49.2 | 0.09*** | 0.04 | |
| IL10 | 8.7 | 2.75*** | 0.24 | |
| IL12p40 | 27.0 | 1.91*** | 0.52 | |
| IL12p70 | 1.3 | 35.49*** | 0.44 | |
| IL13 | 50.5 | 2.12*** | 1.07 | |
| IL15 | 49.2 | 1.00** | 0.49 | |
| IL17 | 43.7 | 0.23*** | 0.10 | |
| IP10 | 54.0 | 11.81*** | 6.37 | |
| MCP1 | 53.9 | 11.33** | 6.10 | |
| MCP3 | 53.5 | 3.94*** | 2.11 | |
| MDC | 54.4 | 0.06*** | 0.03 | |
| MIP1α | 55.6 | 2.81*** | 1.56 | |
| MIP1β | 50.1 | 2.51*** | 1.26 | |
| PDGF-AA | 36.8 | 2.53*** | 0.93 | |
| PDGF-AAAB | 39.9 | 0.01*** | 0.00 | |
| RANTES | 54.6 | 0.05*** | 0.03 | |
| sCD40L | 45.8 | 0.27** | 0.12 | |
| sIL2R | 34.7 | 0.27*** | 0.09 | |
| TGFα | 56.5 | 2.18*** | 1.23 | |
| TNF | 31.2 | 0.46*** | 0.14 | |
| TNFβ | 13.4 | 1.30 | 0.18 | |
| VEGF | 4.2 | 8.16*** | 0.34 |
EGF, epidermal growth factor; G-CSF, granulocyte colony-stimulating factor; GM-CSF, granulocyte macrophage colony-stimulating factor; IFN, interferon; IL, interleukin; RR, relative recovery; TGF, transforming growth factor; TNF, tumour necrosis factor; VEGF, vascular endothelial growth factor; HAS, human albumin solution; FGF2, basic fibroblast growth factor; Flt3 lig, Fms-related tyrosine kinase 3 ligand; IP10, chemokine CXC motif ligand 10; MCP, monocyte chemoattractant protein; MDC, macrophage derived chemoattractant; MIP, monocyte inflammatory protein; PDGF, platelet derived growth factor; sIL2R, soluble interleukin 2 receptor; sCD40L, soluble CD40 ligand.
The 3.5% HAS microdialysis catheter concentrations have been used to calculate a ratio of microdialysate to arterial plasma ratio. As this does not take into account the fact that the microdialysis sample recovers only a fraction of the true extracellular concentration, we have also quoted the estimated brain extracellular/arterial plasma ratio. We have used our previous in vitro measurements of RR (Helmy et al, 2009) where available, and for those cytokines where there is no published data for RR, we have estimated the RR based on apparent molecular weight (Supplementary figure 4). This provides the best estimate for RR available from previously published data; however, we have also included the uncorrected median microdialysate/arterial plasma concentration ratio for transparency. The brain extracelluar/arterial concentration ratio was only calculated for those samples that were taken concurrently and the median quoted for this distribution. The Wilcoxon signed rank test (two-tailed) was used to determine whether there was a statistical difference between the plasma and estimated brain extracellular concentration. The stars in the median [brain extracellular]/[arterial plasma] ratio indicate the level of significance (*P<0.05, **P<0.001, ***P<0.0001). The ‘raw' median [microdialysate]/[arterial plasma] ratio has also been included to show that even without a correction for RR, many of the cytokines have a several-fold higher concentration in microdialysate than in arterial plasma. The square brackets are used to denote concentrations throughout.