Elevated Anti–Annexin V Antibody Levels in Antiphospholipid Syndrome and Their Involvement in Antiphospholipid Antibody Specificities

To clarify the involvement of annexin V (ANX) in antiphospholipid antibody (APA) specificities, we studied antiANX antibodies (aANX) using 2 kinds of enzyme-linked immunosorbent assay plates (plain and gamma-irradiated) and anti-beta 2-glycoprotein I antibodies (a-beta 2GPI) in 53 patients with antiphospholipid syndrome (APS). The incidence of aANX IgG-positive results in the autoimmune APS group was significantly higher than that of healthy control subjects. However, we could not demonstrate a significantly higher incidence in the infection- or drug-induced group. Nor could we find an increased incidence of IgM isotype. When the 2 plates were compared, the discrepancies of positivity were demonstrated in both isotypes. We speculated that these discrepancies between the plate surfaces were attributed to the altered antigenicity of ANX. Although positivity of a-beta 2GPI was associated significantly with clinical manifestations, no significant associations were demonstrated between the incidence of aANX-positive results and clinical manifestations. We inferred that the involvement of aANX in the pathogenic mechanism of APS is unlikely.