iC3b-opsonized apoptotic cells mediate a distinct anti-inflammatory response and transcriptional NF-kappaB-dependent blockade.
In recent years, it has become apparent that the removal of apoptotic cells by macrophages and DC is not only noninflammatory, but also immune-inhibitory, in most although not all circumstances. Complement may be involved in the uptake of apoptotic cells via direct binding of bridging factors in some physiological circumstances, by opsonization and engagement of the complement receptors. In the current study, we use a complement-dependent system of apoptotic cell clearance by human-derived macrophages and DC. Using a luciferase reporter gene and measuring immune response to non-opsonic zymosan, we show that iC3b-apoptotic cells induce NF-kappaB inhibition in response to zymosan and LPS at the nuclear translocation, transcriptional and post-transcriptional levels, leading to profound inhibition of proinflammatory cytokines. In addition, interaction with iC3b-opsonized apoptotic cells is characterized by macrophage secretion of IL-10 and lack of TGF-beta secretion. In conclusion, in cells with iC3b receptors, opsonized apoptotic cells mediate a distinct anti-inflammatory response and transcriptional NF-kappaB-dependent blockage.