3). Similar to the murine experiments, 5% of human PBMC added to the upper transwell compartment crossed the HBMEC layer in 12 h migration experiments as compared to an average of 15% when the barrier only consisted

of the coated porous membrane (n=12, not shown). In line with the murine experiments, the proportion of Treg among CD4+ T cells was significantly higher within the fraction of PBMC that had crossed HBMEC than among the initial PBMC sample added to the upper compartment, the latter approximating the Treg blood frequencies of healthy donors (HD) (n=10, Fig. 3: %Foxp3+ among CD4+ T cells, mean±SD: 3.32±1.36%, range 1.83–6.03% (blood) versus 11.31±5.07%, range 2.81–19.39% (migrated)). Similarly, in vitro HIF-1�� pathway simulation with IFN-γ and TNF-α did not significantly alter the migratory superiority of Treg (14.14±5.29%, range 5.48–22.56% migrated Foxp3+ among CD4+ T cells). Again, check details as seen in the murine experiments, when migrating across porous membranes in the absence of HBMEC, Treg consistently accumulated within the migrated CD4+ compartment as well, but to a lower and non-significant extent (6.16±2.3%, range 3.16–10.51% migrated Foxp3+ among CD4+ T cells). Taken together, under basal, non-inflammatory conditions, human Foxp3 Treg migrate through porous membranes and brain endothelium at higher rates than their non-regulatory counterparts. We further speculated that the enhanced migratory propensity of Treg might contribute to the equilibrium

in tissue immune surveillance under physiological conditions. To further investigate this concept, we tested the migratory potential of Treg derived from RR-MS patients, which have been reported to be dysfunctional by several groups. To date, Treg dysfunctionality has been attributed to their suppressive, antiproliferative capacity in vitro, which has been

shown to be reduced in MS 19. Whether migratory abilities are affected and could therefore contribute to the disturbed immune cell homeostasis in the CNS as well has been elusive so far. Of note, the antiproliferative function Methocarbamol of Treg from HD has been shown to decline with age 19. To exclude potential differences due to an alleged general deterioration of Treg function with age, we matched age and sex of patients and controls. Strikingly, Treg from untreated patients with RR-MS in stable phases of the disease did not accumulate among migrated CD4+ T cells under non-inflammatory conditions, exhibiting transmigratory rates comparable to their non-regulatory counterparts (n=12, Fig. 4A: %Foxp3+ among CD4+ T cells, mean±SD: 3.27±1.54%, range 1.4 to 7.4% (blood) versus 5.11±2.62%, range 2.48–10.96% (migrated)). No significant differences in blood frequencies of CD4+Foxp3+ T cells were observed between HD and patients with RR-MS, which is in accordance to previous reports 14. As expected, administration of inflammatory cytokines to the endothelium significantly increased the proportion of migrated Treg (12.52±4.84%, range 6.87–21.