CTSS and rheumatoid arthritis: There are already excellent reagents for the determination of caspase 1 activity and although historically it has been challenging to develop selective reagents towards CTSS, many recent studies have highlighted new generation ABPs and substrates that may overcome such bottlenecks [46, 47], and indeed already applied to assess CTSS activity levels in the serum of rheumatoid arthritis and osteoarthritis patients to stratify disease states [48].