The invention provides an isolated peptide containing a motif that binds antiphospholipid antibodies (aPLA) and that is recognized by CD4+ T cells that are able to induce production of antiphospholipid antibodies (aPLA). The present invention further provides methods for detection of aPLA and CD4+ T cells able to induce production of aPLA. The present invention also provides methods for treating the antiphospholipid syndrome (APS).