Previous studies using selective STAT inhibitors have demonstrated that the TSLP-mediated type 2 response of CD4 + T cells is driven mainly by STAT6 phosphorylation (Figure ). To assess whether the IL-13 reduction by HS and dPGS10 was due to diminished TSLP-TSLPR interaction, we investigated the phosphorylation state of STAT6. A decrease in STAT6 phosphorylation would be expected in the event of reduced IL-13 release caused by TSLP inhibition. The quantification of STAT6 phosphorylation by western blot shows a significant reduction (p < 0.05) of the phosphorylation state when adding dPGS10 (Figure ) and a less pronounced reduction of the phosphorylation state when adding HS. The dPGS10-mediated pSTAT6 reduction is in line with the observed strong binding to TSLP. A possible explanation for the less pronounced pSTAT6 reduction by HS could be that it requires long periods of time to interact strongly enough with TSLP, and then forms highly stable complexes that cause the observed potent reduction of IL-13 after 36 h. This slow but highly stable complex formation was also observed in SPR studies. Here, the ka was relatively weak, but the kd was comparable to that of the polyglycerol sulfates (see Table ). Thus, the brief 20-minute incubation time in the investigation of STAT6 phosphorylation may not have been long enough to enable fully realized HS-TSLP interaction.