Figure 4.

Synovial fluid tryptase-6 aligns with active serine proteinases from PsA, OA and RA patients. Tryptase-6 was detected by western blot analysis of individual SF samples from PsA, OA and RA patients (A). In parallel, trypsin-like serine proteinase activity was identified in SF samples from the same individuals after covalent labelling with a biotinylated ABP probe for trypsin-like serine proteinases in the presence or absence of the trypsin inhibitor, STI (4 µg/ml), and visualization by western blot detection using streptavidin-HRP (B). An ABP-labelled band at the predicted molecular weight of active tryptase-6 (~25 KDa), for which labelling was reduced in the presence of STI was observed (arrow, B). A column-based antibody affinity chromatography procedure was used to isolate tryptase-6 from PsA SF samples (n=2). The activity of the isolated enzyme and its identity were confirmed by its ability to cleave the substrate, VPR-AMC, and by western blot detection with a tryptase-6 antibody, respectively (C).