We report here the expression of β₂-GPI mRNA by cell types involved in the pathophysiology of the anti-phospholipid syndrome (APS), i.e. endothelial cells as a target of autoantibodies in the APS, astrocytes and neurones involved in APS of the central nervous system (CNS). Lymphocytes were also included in the study, as it has been demonstrated that patients with systemic lupus erythematosus-associated CNS diseases have serum anti-lymphocyte antibodies cross-reacting with brain antigens, and intrathecally synthesized anti-neurone antibodies. Reverse transcriptase-polymerase chain reaction followed by restriction enzyme digestion of the product obtained demonstrated the presence of β₂-GPI mRNA in all cell types here tested, cultured both in presence and absence of fetal calf serum. In both culture conditions, the same cell types were immunoreactive to an anti-β₂-GPI MoAb, as determined by indirect immunofluorescence technique. Taken together, these results indicate a direct cell synthesis of β₂-GPI, suggesting an antigenic function of β₂-GPI in the APS, including the CNS disease that occurs in this syndrome.