Role of attraction and danger signals in the uptake of apoptotic and necrotic cells and its immunological outcome

Abstract

In healthy multicellular organisms dying cells-apoptotic as well as necrotic ones-are swiftly engulfed either by phagocytosis-competent neighbouring cells or by professional phagocytes. The process of dying cell removal with special regard to the key players and the molecular mechanisms involved in this scenario as well as the postprandial reactions of the phagocyte and the immunological outcome is a rapidly evolving field of scientific interest. During the last years numerous studies have led to a detailed understanding of the interaction site between the dying cell and the phagocyte, which today is called the phagocytic synapse, and the current concept that apoptotic cell removal leads to an anti-inflammatory whereas necrotic cell removal stimulates a pro-inflammatory phagocyte reaction. Conversely, our knowledge about the soluble factors released from dying cells is very limited, although meanwhile it is generally accepted that not only the dying cell itself but also the substances, which are liberated during cell death, contribute to the process of dying cell removal as well as to its immunological outcome. Here, we intend to summarize the current knowledge about attraction and danger signals of apoptotic and necrotic cells, their function as chemoattractants in phagocyte recruitment, additional effects on the immune system, and the receptors, which are engaged in this scenario. © 2009 Springer Netherlands.