Not only are some anti-endothelial cell antibodies (AECA) directed to thus far unidentified cell membrane structures, but some ot them recognize "planted" antigens and possibly ligand-receptor complexes. The functional heterogeneity of AECA is widely acknowledged: part of them activate the complement, mediate antibody-dependent cell cytotoxicity of trigger the production of tissue procoagulant factor. It has also recently been established that a proportion of AECA have the capacity to induce apoptosis of their target cells. In fact, the most direct demonstration of the pathogenicity of AECA is the autoantibody-induced murine model of vasculitis.