MX1 and viral infectious disease: Since the theory of viral infection first proposed by Benjamin Landing in 1974, several viruses, including cytomegalovirus (CMV), have been reported to be related to the pathogenesis of BA [8, 9]; however, myxovirus resistance protein 1, the evidence of a preceding viral infection, could be found even in the absence of viral material, thus indicating that the virus infection detected may just be a coincidental prior event, and neither epidemiological investigations nor in vivo virological tests of BA patients confirm a certain virus that causes BA [10, 11].