Rapid and strong induction of apoptosis in human Eosinophils by Anti-CD30 mAb-coated microspheres and phagocytosis by macrophages

Background: Eosinophils represent a potential therapeutic target in allergic diseases. We previously reported that two clones of anti-CD30 mAbs (HRS-4 and Ber-H8) induced extremely rapid and intense apoptosis in human eosinophils in vitro, but only when the mAbs were immobilized on plates [Matsumoto K, J Immunol 2004;172:2186]. As the initial step towards clinical application of these anti-CD30 mAbs in the treatment of allergic diseases, we made an attempt to clarify two issues; first, whether or not anti-CD30 mAb-coated microspheres can efficiently induce apoptosis in human eosinophils, and second, whether or not these apoptotic eosinophils can be phagocytosed by macrophages without the release of granular proteins. Methods: Purified human eosinophils were treated with anti-CD30 mAb-coated polystyrene microspheres (diameter, 1.44 μm). Apoptosis was determined by annexin V-binding. For the phagocytosis assay, eosinophils were co-cultured with monocyte-derived human macrophages or PMA-pretreated U-937 cells. Phagocytosis was determined by light microscopy and by the eosinophil-derived neurotoxin (EDN) concentration in the supernatant. Results: Anti-CD30 mAb-coated, but not control lgG1-coated microspheres significantly reduced eosinophil survival in a dose-dependent manner. Marked phagocytosis of the apoptotic eosinophils by macrophages was also observed when the eosinophils were treated with anti-CD30 mAb-coated microspheres. The apoptotic eosinophils released large amounts of EDN in the absence of macrophages; however, the EDN levels were significantly decreased when the eosinophils were co-cultured with macrophages. Conclusions: Anti-CD30 mAb-coated microspheres are capable of inducing rapid and strong apoptosis in human eosinophils. Furthermore, the apoptotic eosinophils were also phagocytosed by macrophages with minimal release of the granular proteins.