CD46 Plays a Key Role in Tailoring Innate Immune Recognition of Apoptotic and Necrotic Cells

Kristina Elward,Mark Griffiths,Masashi Mizuno,Claire L Harris,Jim W Neal,B Paul Morgan,Philippe Gasque

doi:10.1074/jbc.m506579200

Abstract

Complement is the canonical innate immune system involved in host defense and tissue repair with the clearance of cell debris. In contrast to the robust armory mounted against microbial nonself-pathogens, complement is selectively activated on altered self (i.e. apoptotic and necrotic cells) to instruct the safe demise by poorly characterized mechanisms. Our data shed new light on the role of complement C1q in sensing nucleic acids (NA) rapidly exposed on apoptotic Jurkat T cell membranes and in driving C3 opsonization but without the lytic membrane attack complex. DNA/RNase-treated apoptotic cells failed to activate complement. We found that several other apoptotic cell models, including senescent keratinocytes, ionophore-treated sperm cells, and CMK-derived platelets, stained for cleaved caspase 3 were rapidly losing the key complement regulator CD46. CD46 from nuclear and membrane stores was found to cluster into blebs and shed into microparticles together with NA, phosphatidylserine, C1q, and factor H. Classical and alternative pathways of complement were involved in the recognition of H2O2-treated necrotic cells. Membrane attack complex was detected on necrotic cells possibly as a result of CD46 and CD59 shedding into soluble forms. Our data highlight a novel and universal paradigm whereby the complement innate immune system is using two synergistic strategies with the recognition of altered self-NA and missing self-CD46 signals to instruct and tailor the efficient removal of apoptotic and necrotic cells in immunoprivileged sites.

Highlights

Selective innate immune recognition is established essentially according to particular molecular patterns (i.e. apoptotic cell-associated molecular patterns (ACAMPs),2 pathogenic protein-associated molec
The best characterized example of the marker of self is the recognition of the major histocompatibility complex class I molecules by various inhibitory receptors expressed on natural killer (NK) cells [22]
When the camptothecin-treated cells were analyzed by FACS, we clearly identified three distinct cell populations as follows: viable cells, cells stained with propidium iodide (PI) but not with annexin V, and cells stained with PI and annexin V

Summary

Introduction

Selective innate immune recognition is established essentially according to particular molecular patterns (i.e. apoptotic cell-associated molecular patterns (ACAMPs), pathogenic protein-associated molec-. C1q was first shown to bind to antigen-antibody complexes, but it is increasingly evident that C1q multimeric structure is key to the selective recognition of apoptotic cells, toxic amyloid fibrils, and the pathogenic prion agent by mechanisms that remain poorly understood (10 –18) These events will lead to the opsonization of the target with C1q, C4, and C3 opsonins recognized by macrophages bearing complement pattern-recognition receptors such as CR1, CR3, and CR4 (where CR indicates complement receptor) [7, 19, 20]. Innate immune recognition is based on recognition of molecular markers specific for self to prevent uncontrolled phagocytosis [3] These markers are gene products expressed only on the surface of normal uninfected cells of the host but not on microbial cells. Complement plays a critical role in the scavenging of toxic cell debris for safe and efficient removal by phagocytes before

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Conclusion