We repeated the above experiments with wild-type mice and two modifications: (1) incubating macrophages with human sera pooled from ACPA+ or ACPA- RA subjects instead of anti-citH4 antibody and (2) permeabilization after incubation with sera, instead of before, to better mimic the endogenous biology as opposed to the goal of detecting histone citrullination in all cells. Here, PRTN3 is linked to rheumatoid arthritis.