PRTN3 and rheumatoid arthritis: Based on an evident ACPA cross-reactivity between citrullinated host proteins and EBV-citrullinated peptides, which not only entail citrullinated EBV proteins but also other virus proteins and host proteins, antibody cross-reactivity between ACPAs and citrullinated proteins appears, at first glance, to relate to cross-reactivity between infectious non-self and self-tissue antigens associated with RA, but it does not appear to be the cause of RA; hence, the role of molecular mimicry in the onset of RA is not supported.