Receptor antagonists reduced interleukin 8 and chemokine (C-C motif) ligand 18 secretion, inhibiting effects are not additive. (A) Interleukin 8 (IL-8) and (B) chemokine (C-C motif) ligand 18 (CCL18) concentrations in the supernatants of peripheral blood mononuclear cells (PBMCs) from healthy donors after 8 hours of in vitro stimulation by immunoglobulin G of systemic sclerosis patients (SSc-IgG) after pretreatment with either the angiotensin II receptor type 1 blocker valsartan (Val) or the endothelin receptor type A blocker sitaxsentan (Sit), measured by enzyme-linked immunosorbent assay (ELISA) and normalized to the corresponding sample without any antagonist representing 100%. Data are derived from one experiment done with 26 SSc-IgG. Simultaneous blocking with both antagonists did not improve the inhibiting effects: (C) IL-8 and (D) CCL18 concentrations in the supernatants of PBMCs from three healthy donors after 8 hours of in vitro stimulation by SSc-IgG after pretreatment with valsartan (Val) or sitaxsentan (Sit) or both (Val + Sit) measured by ELISA and normalized to the corresponding samples without any antagonist representing 100%. Data derived from three independent experiments done with pooled IgG from thirteen SSc patients. Statistical analysis was done by Wilcoxon matched-pairs test. Medians (A and B) and medians with range (C and D) are shown. ***P < 0.001.