Anti-β<SUB>2</SUB>-glycoprotein I antibodies in children with atopic dermatitis

β₂-Glycoprotein I (β₂GPI) appears to be the major antigen for antiphospholipid antibodies (aPL) in patients with antiphospholipid syndrome (APS). In early infancy, virtually all children initiate transient immune response to non-pathogenic nutritional antigens, which fails to terminate in children with atopic diseases. To examine the possibility that a prolonged immune response to β₂GPI could also spread to the human protein, antibodies against human β₂GPI (anti-β₂GPI) were determined in 93 randomly selected children with different allergic diseases. A high frequency (42%) of IgG anti-β₂GPI was found in children with atopic dermatitis (AD), but not in those with other allergic diseases. Anti-β₂GPI in children with AD were exclusively of the IgG1 subclass and bound to bovine β₂GPI as well, but not to either β₂GPI combined with the phospholipid cardiolipin. The epitopes were identified in domain V of β₂GPI and the antibody binding was abolished upon the specific proteolytic cleavage of the phospholipid-binding C-terminal loop in domain V of β₂GPI. These results indicated that the epitopes for anti-β₂GPI in children with AD most likely resided in close vicinity of the phospholipid-binding site of β₂GPI. The epitopic difference from anti-β₂GPI in APS may explain presumed non-thrombogenicity of anti-β₂GPI in children with AD.