CCL21 and systemic sclerosis: However, in the Luminex analyses, CCL21 levels were similar in SSc-PAH patients (n=72) compared to SSc patients with no PH (n=107) by RHC (0.56 ± 0.63ng/ml vs. 0.52 ± 0.73ng/ml, p=0.737) (Figure 4B, ii).