“…One of the suspects for such an agent is a virus because viral infections such as rubella, human parvovirus B19 (B19), cytomegalovirus (CMV), human T cell leukemia virus 1, and HIV often cause an acute onset of polyarthritis (1)(2)(3)(4)(5). Some cases with acute B19 infection are well known to present clinical symptoms resembling RA (1)(2)(3), and the presence of B19 DNA has been demonstrated in autoimmune diseases such as RA, systemic lupus erythematosus, adult-onset Still's disease, and polyarteritis nodosa (6)(7)(8). Although the expression of B19 protein or its isolation from the affected organ is critical to know the role of the virus in vivo, these have remained unelucidated.…”