(a) HEK293T cell cultures were treated with 50μM of Abcc1 inhibitor MK571 or the diluted carrier (DMSO) for 16hr. Collected supernatant was used at a 1:10 dilution in a bioassay based on the transwell migration of P2RY8+ WEHI cells towards CXCL12. Control wells contained CXCL12, CXCL12 + DMSO, or CXCL12 + 5μM MK571. (b) Activated, purified splenic B cells from Abcc1−/− and control (Abcc1+/+ and +/− littermate) mice were incubated for 72hrs, after which the supernatant was collected and measured for GGG by LC-MS/MS (n= 14 control, n=11 Abcc1−/−). Data are pooled from (b) or representative of (a) three (b) experiments. P-values determined by unpaired two-tailed Student’s t-test (a,b). *P<0.05, **P<0.01, ***P<0.001, ****P<0.0001. Graphs depict mean with s.d. and points represent (a) technical or (b) biological replicates.