In the current study, we have analyzed sera from RA patients for ACPA responses against peptides mimicking the endogenously citrullinated epitopes, in the form of citrullinated peptides generated in vitro, and also investigated if these epitopes could be employed to target purified anti-CCP2 immunoglobulin G (IgG) molecules. The gene discussed is PRTN3; the disease is rheumatoid arthritis.