IGG SUBCLASS RESPONSE TO HUMAN PARVOVIRUS B19 INFECTION

Background: IgG antibodies are essential to immunity against human par vovirus B19 and can neutralize infection both in bone marrow cell cult ures infected in vitro and in chronically infected immunosuppressed in dividuals. Objectives: To assess the levels and response kinetics of I gG subclasses towards individual structural proteins of human parvovir us B19. Study design: Subclasses of IgG for capsid proteins VP1 or VP2 were quantified by EIA using monoclonal antibodies in 30 acutely infe cted and 30 convalescent patients, as well as in 32 remotely infected and 20 non-infected controls. Results: In all groups of seropositive i ndividuals the predominant subclass for either structural protein was IgG1. Subclass IgG3 was associated with acute infection. By contrast, IgG4 appeared months after infection, and occurred specifically toward s VPI. The ratio of VP1-specific subclasses IgG3 and IgG4 provided a d iagnostic test for recent infection with a specificity of 98% and a se nsitivity of 97%. Conclusions: Comparative measurement of VP1-specific IgG3 and lgG4 is useful in diagnosis. The IgG4 results point to long- term expression of immunologically active VP1 and to T-cell help of T( h)2 type for B-cells recognizing VP1.