Functional heterogeneity of anti-endothelial cell antibodies

While it has been claimed that some anti-endothelial cell antibodies (AECA) activate EC, there is also evidence that others trigger apoptosis. To addr ess the issue of whether activation is a prerequisite for AECA-mediated apo ptosis of EC, 23 AECA-positive sera were evaluated for their ability to ind uce activation and/or apoptosis. Activation was defined as an over-expressi on of E-selectin and intercellular adhesion molecule 1. Optical microscopy, annexin V binding, hypoploid cell enumeration, and determination of poly ( ADP-ribose) polymerase cleavage-related products were used to assess apopto sis. Four functional profiles were defined: 10 sera promoted activation and apoptosis (act+/apo+), one was act+/apo-, six act-/apo+, and the remaining six act-/apo-. The reduced membrane expression of thrombomodulin was assoc iated with apoptosis, rather than activation. Caspase-3 was implicated in t he two models of apoptosis, the ratios of several survival proteins to Bax decreased, regardless of the ability of apo+ AECA to activate the cells, wh ile radical oxygen species did not appear to be involved. Furthermore, it o ccurred that macrophages engulfed EC treated with apoptosis-promoting AECA, but not those incubated with AECA that did not induce apoptosis. Hence, AE CA represent an extremely heterogeneous family of autoantibodies, not only because of the variety of their target antigens, but also the subsequent di versity of their effects.