0.05),and no significant relationship were observed between the A? autoantibody and the severity of dementia or the natural course.TAPIR positive plasma showed a stronger immunoaffinity with monomeric and dimeric A?40 and FA? than with monomeric A?42,but a weak immunoaffinity with dimeric A?42.Conclusions Naturally existing plasma antibodies to A? might not be an useful biomarker for AD diagnosis,and could not affect clinical signs and natural progress of AD.