Figure 1.

Wild type (WT) K/BxN serum transfer mice generate synovial neutrophil extracellular traps (NETs). Mice were injected with K/BxN serum on days 0 and 2 and sacrificed on day 5. Synovial cells were flushed from the ankle joint (A) and peripheral blood was collected from the venous plexus of arthritic or healthy mice (B) and stained with antibodies to citrullinated histone H4 and 4',6-diamidino-2-phenylindole (DAPI). Histone citrullination and NETs were readily detectable in the arthritic joints of WT mice, but were not observed in peptidyl arginine deiminase 4 knockout (PAD4 KO) K/BxN mice or WT healthy controls (A). Histone citrullination was present in the peripheral blood of WT K/BxN mice, however, no NET formation was observed. Images were taken at 80× magnification and are representative of at least three independent experiments with two mice per experimental group.