Elsevier

Clinical Immunology

Volume 112, Issue 2, August 2004, Pages 175-182
Clinical Immunology

Apoptosis, subcellular particles, and autoimmunity

https://doi.org/10.1016/j.clim.2004.02.017Get rights and content

Abstract

Firm evidence links the process of apoptosis to the induction of autoimmune disease. However, questions remain regarding the precise interactions of dying cells with the immune system. Genetic analyses indicate that deficiencies in serum proteins or receptors that mediate clearance of apoptotic cells increase the risk of autoimmunity. Moreover, administration of apoptotic cells to naive animals elicits transient autoimmune responses. Because known autoantigens are covalently modified and redistributed to cell surface blebs during the execution stage of apoptosis, increasing attention is being directed at this stage of programmed cell death, and researchers have identified a variety of autoantigens that are sequestered within blebs. However, blebs are merely a transition stage toward the complete cellular fragmentation, as blebs quickly convert into apoptotic bodies, subcellular particles (SCPs) of heterogeneous size, surface composition, and cargo. Because certain types of subcellular particles represent packets of highly enriched autoantigens, we propose that they are relevant to our understanding of autoimmunity.

Introduction

In an account of the seminal experiments that lead to the discovery of apoptosis as the genetically programmed pathway of cell death, Kerr [1] describes the initial observation of apoptotic bodies, subcellular particles (SCPs) resulting from cellular condensation and fragmentation. Microscopy of histologic preparations of ischemic liver, basal cell carcinoma, and adrenal glands in neonate animals consistently revealed small, round particles suggesting a mode of cell death that was distinct from necrosis [2]. The ultrastructural features of such SCPs allowed the investigators to conclude that SCPs are the final products of a process that begins with the condensation of nuclear chromatin and the aggregation of chromatin against the nuclear envelope. Subsequently, the nuclear envelope constricts in several locations to generate nuclear fragments that independently move to the cell surface and form surface protrusions, later called blebs [3]. The blebs separate from the remainder of the cell and cause membrane-bound SCPs containing nuclear fragments or remnants of the cytoplasm. These particles are taken up by surrounding cells and specialized phagocytes [2].

In light of the enormous impact that the initial description of apoptosis had on biology, it is important to recognize that several years earlier, apoptotic bodies were observed to play a unique role as protagonists in the disease process of systemic lupus erythematous (SLE). Microscopic examination of bone marrow biopsies from SLE patients consistently revealed polymorphonuclear leukocytes that had ingested fragments of apoptotic nuclei from other cells [4]. These unusual cells containing additional nuclei beside their own were called LE cells and were recognized as reliable diagnostic markers for SLE. Soon thereafter, it became clear that a factor from SLE sera was required to allow phagocytosis of SCPs containing apoptotic nuclear fragments. Kanai et al. [5] isolated an antibody to a conformational epitope composed of DNA and histones that could mediate the uptake of nuclear fragments by phagocytes. Other researchers identified LE cells in aspirates taken from synovial fluids, cerebrospinal fluids, and pleural effusions of SLE patients [6]. However, despite the conceptual advance that the discovery of the LE cell provided for our understanding of SLE, relatively few studies explored the possible connection between the release of nuclear fragments in apoptosis and the induction of autoantibodies to nucleoprotein antigens.

Section snippets

Molecular mechanisms of apoptotic cell clearance

Apoptotic cell clearance depends on specific phagocyte receptors and serum proteins that facilitate apoptotic cell recognition. Separate, yet complementary pathways contribute toward the recognition of cells in early versus late stages of apoptosis [7], [8], [9].

Among the earliest signs of apoptosis is the cell surface exposure of phosphatidylserine, a phospholipid that remains confined to the inner plasma membrane in most viable cells [10]. The identification of phosphatidylserine as one of

Tissue-specific clearance mechanisms

Depending on the location where cell death occurs, clearance of apoptotic cells may be accomplished in different ways. Important variables include the rate of cell turnover, the type of cell that undergoes apoptosis, the type of phagocyte that ingests the dying cell, the receptor(s) used for apoptotic cell recognition, and the stage of apoptosis at which the apoptotic cell is recognized and engulfed. For example, Kupffer cells of the liver [45] and macrophages of the splenic red pulp [46]

Defective clearance and autoimmunity

Efficient and complete clearance of apoptotic remnants is crucial for the avoidance of autoimmunity. This was demonstrated by the increased prevalence of autoimmune responses in individuals with decreased function of C1q or C4 complement components [39]. In fact, homozygous deficiency of C1q represents the greatest known single risk factor for SLE [54]. The production of autoantibodies and incidence of glomerulonephritis that characterize human complement deficiencies have been reproduced in

Late stages of apoptosis and the induction of autoimmunity

How can the idea that apoptotic cells induce autoimmunity be reconciled with the fact that apoptosis is a necessary and ubiquitous feature of tissue homeostasis in multicellular organisms? One important consideration is that apoptosis is a progressive chain of events in which an initiating signal is transmitted through a network of specialized enzymes [75] until, over time, nearly all cellular contents have been modified in unique ways. Many cellular components are cleaved by caspases and as a

Synopsis of research from the authors' laboratory

Our work has explored the circumstances that lead to the induction of systemic autoimmune responses to nuclear antigens [82], [83]. Nuclear antigens are packaged within large apoptotic blebs that cause SCPs containing tightly packed DNA and are bound by remnants of the nuclear envelope. We have considered the possibility that nuclear antigens derived from apoptotic cells can initiate and sustain an autoimmune response [74], [82]. Antibodies from mouse models of SLE and APS may be particularly

Prospects for the future

Research exploring the relationship between apoptosis and the induction of autoimmunity is rapidly gaining momentum. Within the near future, conclusive proof for the role of apoptosis in providing autoantigenic stimuli will be provided. Soon, even greater efforts will be marshaled to explore the precise molecular connections between the effects of apoptotic modifications in different tissues and the induction of disease-specific autoantibodies. In addition, we anticipate that defects in

Acknowledgements

We thank Dr. Marc Monestier for the kind gift of the purified FC3 antibody and Mr. Tim Higgins, senior illustrator, for graphical arts. The research in the authors' laboratory was supported by the NIAID (AI054938), an institutional grant from the University of Tennessee Health Sciences Center, the Center of Excellence in Structural Biology, the Center of Excellence for Diseases of Connective Tissue, and the UT Rheumatic Disease Research Core Center of the National Institutes of Health.

References (86)

  • G.J Arlaud et al.

    Structural biology of the C1 complex of complement unveils the mechanisms of its activation and proteolytic activity

    Mol. Immunol.

    (2002)
  • Y.B Shui et al.

    Morphological observation on cell death and phagocytosis induced by ultraviolet irradiation in a cultured human lens epithelial cell line

    Exp. Eye Res.

    (2000)
  • R Parnaik et al.

    Differences between the clearance of apoptotic cells by professional and non-professional phagocytes

    Curr. Biol.

    (2000)
  • T Nakano et al.

    Cell adhesion to phosphatidylserine mediated by a product of growth arrest-specific gene 6

    J. Biol. Chem.

    (1997)
  • G Lemke et al.

    Macrophage regulation by Tyro 3 family receptors

    Curr. Opin. Immunol.

    (2003)
  • M Katagiri et al.

    Mechanism of stimulation of osteoclastic bone resorption through Gas6/Tyro 3, a receptor tyrosine kinase signaling, in mouse osteoclasts

    J. Biol. Chem.

    (2001)
  • L Fesus et al.

    Transglutaminase 2: an enigmatic enzyme with diverse functions

    Trends Biochem. Sci.

    (2002)
  • T Maekawa et al.

    Impairment of splenic B and T lymphocytes in the early period after severe thermal injury: immunohistochemical and electron microscopic analysis

    Burns

    (2002)
  • J.F Kerr et al.

    Apoptosis: a basic biological phenomenon with wide-ranging implications in tissue kinetics

    Br. J. Cancer

    (1972)
  • L.A Casciola-Rosen et al.

    Autoantigens targeted in systemic lupus erythematous are clustered in two populations of surface structures on apoptotic keratinocytes

    J. Exp. Med.

    (1994)
  • M.M Hargraves et al.

    Presentation of two bone marrow elements; the ‘tart’ cell and ‘LE’ cell

    Proc. Staff Meet. Mayo Clin.

    (1948)
  • M.M Hargraves

    Discovery of the LE cell and its morphology

    Mayo Clin. Proc.

    (1969)
  • S Somersan et al.

    Tethering and tickling: a new role for the phosphatidylserine receptor

    J. Cell Biol.

    (2001)
  • J Savill et al.

    Corpse clearance defines the meaning of cell death

    Nature

    (2000)
  • V.A Fadok et al.

    Phagocyte receptors for apoptotic cells: recognition, uptake, and consequences

    J. Clin. Invest.

    (2001)
  • V.A Fadok et al.

    Exposure of phosphatidylserine on the surface of apoptotic lymphocytes triggers specific recognition and removal by macrophages

    J. Immunol.

    (1992)
  • V.A Fadok et al.

    A receptor for phosphatidylserine-specific clearance of apoptotic cells

    Nature

    (2000)
  • O.D Moffatt et al.

    Macrophage recognition of ICAM-3 on apoptotic leukocytes

    J. Immunol.

    (1999)
  • P.R Hoffmann et al.

    Phosphatidylserine (PS) induces PS receptor-mediated macropinocytosis and promotes clearance of apoptotic cells

    J. Cell Biol.

    (2001)
  • B Bouma et al.

    Adhesion mechanism of human beta(2)-glycoprotein I to phospholipids based on its crystal structure

    EMBO J.

    (1999)
  • M.F Harper et al.

    Characterization of beta2-glycoprotein I binding to phospholipid membranes

    Thromb. Haemost.

    (1998)
  • J.S Levine et al.

    The antiphospholipid syndrome

    N. Engl. J. Med.

    (2002)
  • J.H Rand

    The antiphospholipid syndrome

    Annu. Rev. Med.

    (2003)
  • B.E Price et al.

    Anti-phospholipid autoantibodies bind to apoptotic, but not viable, thymocytes in a beta 2-glycoprotein I-dependent manner

    J. Immunol.

    (1996)
  • M Stern et al.

    Human monocyte-derived macrophage phagocytosis of senescent eosinophils undergoing apoptosis. Mediation by alpha v beta 3/CD36/thrombospondin recognition mechanism and lack of phlogistic response

    Am. J. Pathol.

    (1996)
  • A.J Szalai et al.

    C-reactive protein: structural biology, gene expression, and host defense function

    Immunol. Res.

    (1997)
  • K.B Reid

    Proteins involved in the activation and control of the two pathways of human complement

    Biochem. Soc. Trans.

    (1983)
  • J.R Wright

    Immunomodulatory functions of surfactant

    Physiol. Rev.

    (1997)
  • S.J Kim et al.

    Opsonization of apoptotic cells and its effect on macrophage and T cell immune responses

    Ann. N. Y. Acad. Sci.

    (2003)
  • H.X Jiang et al.

    Binding and complement activation by C-reactive protein via the collagen-like region of C1q and inhibition of these reactions by monoclonal antibodies to C-reactive protein and C1q

    J. Immunol.

    (1991)
  • S.J Kim et al.

    I-PLA(2) activation during apoptosis promotes the exposure of membrane lysophosphatidylcholine leading to binding by natural immunoglobulin M antibodies and complement activation

    J. Exp. Med.

    (2002)
  • M.K Chang et al.

    C-reactive protein binds to both oxidized LDL and apoptotic cells through recognition of a common ligand: phosphorylcholine of oxidized phospholipids

    Proc. Natl. Acad. Sci. U. S. A.

    (2002)
  • A Familian et al.

    Chromatin-independent binding of serum amyloid P component to apoptotic cells

    J. Immunol.

    (2001)
  • Cited by (83)

    • Molecular pattern recognition in peripheral B cell tolerance: lessons from age-associated B cells

      2019, Current Opinion in Immunology
      Citation Excerpt :

      Foundational work showed that the endosomal nucleic acid sensors TLR7 or TLR9 are essential for maximal activation of rheumatoid factor expressing B cells stimulated by chromatin-containing immune complexes [21,22]. These and subsequent findings have forged a link between nucleic acid sensing TLRs and the long-recognized fact that many autoantibodies bind components of RNA-containing and DNA-containing complexes, and that inefficient clearance of apoptotic debris is a major source of such antigens, even in the absence of infection [23]. Critical roles for nucleic acid sensing TLRs and their downstream signaling machinery in promoting humoral autoimmunity are now widely confirmed both in mouse models and in human disease (reviewed in Refs. [24,25]).

    • Cell death in the pathogenesis of systemic lupus erythematosus and lupus nephritis

      2017, Clinical Immunology
      Citation Excerpt :

      In summary, many types of post-translational histone modifications are generated during the apoptotic process. Various post-translational modifications that take place during apoptosis could create neoantigens that become targets for autoantibody formation [12,116]. Indeed, experiments performed by several groups suggest that apoptosis-induced post-translational histone modifications are targets for autoimmune responses in SLE patients and mice [117–120].

    • Exosomes: Therapy delivery tools and biomarkers of diseases

      2017, Pharmacology and Therapeutics
      Citation Excerpt :

      The classification of EVs as a heterogeneous mixture of membrane particles has been inconsistent and somewhat confusing. Three major populations have been distinguished: (i) exosomes, initially defined as 50–100 nm lipid bilayer particles released from cells; the size range was then increased to include particles as small as 20 nm in diameter and those as large as 150 nm in diameter, although a size range of 30–100 nm was used in most studies; (ii) microvesicles, also referred to as shedding vesicles (Shedden, Xie, Chandaroy, Chang, & Rosania, 2003) or microparticles (Shantsila, Kamphuisen, & Lip, 2010), which tend to be larger than exosomes (size range: 50–1000 nm); (iii) apoptotic bodies (size range: 50–5000 nm), which result from the fractionation of the cellular content of cells that die by apoptosis (Cline & Radic, 2004; Hristov, Erl, Linder, & Weber, 2004). As apparent, these populations of EVs overlap in size.

    View all citing articles on Scopus
    View full text