Antibodies against the N-terminal domain of annexin A2 in antiphospholipid syndrome

Annexin A2 (ANXA2, an endothelial cell receptor for plasminogen and tissue plasminogen activator) has been identified as a new autoantigen in antiphospholipid syndrome (APS). The aim of the present study was to evaluate the presence of antibodies against the N-terminal domain of annexin A2 (ANXA2) in primary APS (PAPS). By using a synthetic peptide corresponding to the 31 N-terminal amino acids of ANXA2 (ANXA2N31) as an antigen, we performed an enzyme-linked immunosorbent assay (ELISA) to measure anti-ANXA2N31 IgG and IgM antibodies in the serum of PAPS patients (n = 19), systemic lupus erythematosus (SLE) patients (n = 50) and healthy blood donors (n = 106). We did not find any statistically differences between the three groups in terms of IgG and IgM anti-ANXA2N31 titres. Elevated IgG anti-ANXA2N31 titres were not observed in the serum of PAPS or SLE patients who had previously tested positive for anti-ANXA2 antibodies. Thus, the ANXA2 N-terminal domain does not appear to be the target antigen for anti-ANXA2 antibodies in APS.