Interaction of mAb to angiotensin-converting enzyme (ACE) with antigen in vitro and in vivo: antibody targeting to the lung induces ACE antigenic modulation.

We previously described that mAb to angiotensin-converting enzyme (ACE), mAb 9B9, accumulates in the rat lungs after systemic injection. In the present work we have documented that mAb 9B9 cross-reacts with human, monkey, rat, cat and hamster ACE, while other ACE antibodies did not cross-react with the rat, cat and hamster enzyme. Anti-ACE mAb 3A5 and I2H5 inhibit human ACE in vitro, while mAb 9B9 does not inhibit ACE activity. Radiolabeled mAb 9B9, but not other antibodies, accumulates selectively in rat, cat and hamster lungs after systemic administration. No accumulation of mAb 9B9 has been observed in hamster kidney, while hamster kidney ACE activity is higher than that in the lung. mAb 9B9 does not induce complement-mediated injury to cultured endothelial cells. No pathological changes were detected in organs of animals after mAb 9B9 injection (10-100 mg/kg). However, injection of these amounts of mAb 9B9 leads to a decrease in ACE activity in the lung homogenates and an increase in serum. In cultured human endothelial cells treatment with mAb 9B9 increases ACE activity in cell medium and decreases in cell lysates. Therefore, while mAb 9B9 does not kill endothelial cells, at high dose it may induce ACE shedding from the cell. The results obtained support the potential of anti-ACE mAb 9B9 for targeting to the lung and for investigations of the pulmonary endothelium.