Cutting Edge: Differential Effect of Apoptotic Versus Necrotic Tumor Cells on Macrophage Antitumor Activities

Abstract

Macrophages (Mφ) play essential roles both in tumor defense and normal tissue homeostasis by removal of transformed as well as damaged and disintegrating cells. Whereas tissue necrosis is known to provoke inflammatory responses, removal of apoptotic cells has been assumed to be immunologically inert. We now show that while Mφ exposure to necrotized tumor cells causes pronounced stimulation of Mφ antitumor activity, exposure of Mφ to apoptotic tumor cells in contrast results in impairment of Mφ-mediated tumor defense and even support of tumor cell growth. Given the fact that apoptosis is a consequence of various cancer treatment modalities, this may lead to a suppression of local antitumor reactions and thus actually counteract endogenous immune-mediated tumor defense mechanisms.