Anti-β₂-glycoprotein I IgG antibodies from 1-year-old healthy children born to mothers with systemic autoimmune diseases preferentially target domain 4/5: might it be the reason for their 'innocent' profile?

BACKGROUND: Anti-β₂-glycoprotein-I (anti-β₂GPI) were demonstrated to be pathogenic in the antiphospholipid syndrome (APS). However, they can be detected in patients with no features of APS, especially those affected by systemic autoimmune diseases (SAD), and so in healthy children. It has been suggested that anti-β₂GPI against domain 1 (D1) associate with thrombosis, while those recognising domain 4/5 (D4/5) are present in non-thrombotic conditions.

OBJECTIVE: To evaluate the fine specificity of anti-β₂GPI in adults and infants.

METHODS: Three groups were examined-group A: 57 1-year-old healthy children born to mothers with SAD; group B: 33 children with atopic dermatitis; group C: 64 patients with APS.

SUBJECTS: were selected based on positive anti-β₂GPI IgG results. Serum samples were tested for anti-β₂GPI IgG D1 and D4/5 using research ELISAs containing recombinant β₂GPI domain antigens.

RESULTS: Children (A and B) displayed preferential IgG reactivity for D4/5, whereas patients with APS were mainly positive for D1. No thrombotic events were recorded in groups A and B.

CONCLUSIONS: The specificity for D4/5 suggests that anti-β₂GPI IgG production in children born to mothers with SAD is a process neither linked to systemic autoimmunity nor related to the maternal autoantibody status. This unusual fine specificity might, at least partially, account for the 'innocent' profile of such antibodies.