[Subpopulations of anti-β₂glycoprotein I antibodies with different pathogenic potential: fine specificity against the domains of β₂glycoprotein I].

Objective: Anti-β₂glycoprotein I antibodies (a-β₂GPI) are a laboratory criterion for the antiphospholipid syndrome (APS) and were demonstrated to be involved in the pathogenesis of APS. However, they can also be detected in asymptomatic subjects. It has been suggested that a-β₂GPI against Domain1 (D1) associate with thrombosis, while those recognizing Domain4/5 (D4/5) have been identified in non-thrombotic conditions. We evaluate the specificity of a-β₂GPI in different clinical situations.

Methods: We studied 39 one-year-old healthy children born to mothers with systemic autoimmune diseases (SAD) (15 (38.4%) were born to mothers who were a-β₂GPI positive), 33 children with atopic dermatitis (AD) and 55 patients with APS (50 adults and 5 paediatrics). All subjects were IgG a-β₂GPI positive. IgG a-β₂GPI were performed by homemade ELISA, while IgG a-β₂GPI D1 and D4/5 were tested on research ELISAs containing recombinant β₂GPI domains antigens.

Results: One-year-old children and AD children displayed preferential reactivity for D4/5; patients with APS recognized preferentially D1. We also found a good correlation between a-β₂GPI and D4/5 in one-year-old (r=0.853) and AD children (r=0.879) and between a-β₂GPI and D1 in the APS group (r=0.575). No thrombotic events were recorded in both groups of children.

Conclusions: A-β₂GPI found in non-thrombotic conditions (healthy children born to mothers with SAD and AD children) mostly recognize D4/5, in contrast to the prevalent specificity for D1 in the APS group. The different specificity could at least partially explain the "innocent" profile of a-β₂GPI in children.