Fig. 4

a–e IHC staining for CD31 on ST of patients with naïve or MTX-IR PsA and Ab^neg RA patients. Example photos of CD31 (DAB) staining of ST biopsies from patients with naïve (a) or MTX-IR (b) PsA and with naïve (c) or MTX-IR (d) Ab^neg RA (magnification × 20 and magnification × 40 in the corresponding inset). Thin black arrows indicate CD31⁺ vessels (brown) in the corresponding inset. e Synovial CD31⁺ vessel count in PsA and Ab^neg RA patients divided by treatment regimen; *p = 0.01, naïve vs MTX-IR PsA patients; *p < 0.001, naïve vs MTX-IR Ab^neg RA patients. IHC immunohistochemistry, PsA psoriatic arthritis, RA rheumatoid arthritis, Ab autoantibody, MTX-IR methotrexate inadequately responder, CD cluster designation