Endogenous PTX3 translocates at the membrane of late apoptotic human neutrophils and is involved in their engulfment by macrophages

Abstract

Neutrophils are short-lived innate immune cells that rapidly die by apoptosis. A rapid and efficient clearance of apoptotic cells is crucial to avoid autoimmunity. This process involves cell alterations, endocytic receptors expressed by phagocytic cells and soluble bridging molecules (opsonins) that facilitate internalization of apoptotic cells by phagocytes. Neutrophils constitutively express the prototypic long pentraxin PTX3 that binds to apoptotic cells and modulates their clearance. We thus evaluated whether endogenous PTX3 may interfere with the capture of apoptotic neutrophils. We observed that PTX3 accumulates in blebs at the surface of late apoptotic neutrophils, resulting from its active translocation from granules to the membrane. A neutralizing anti-PTX3 monoclonal Ab (mAb) inhibits the capture of late apoptotic neutrophils by macrophages. This study shows that intracellular PTX3 translocates at the surface of late apoptotic neutrophils and acts as an 'eat-me' molecule for their recognition and capture by macrophages. Apoptosis is a physiological cell death process involved in embryogenesis, tissue turnover and resorption of inflammation. Apoptotic cells are rapidly and efficiently cleared by professional and non-professional phagocytic cells. They do not release proinflammatory intracellular components, such as high-mobility group box-1, 1 thereby avoiding phagocyte activation. Apoptotic cells trigger an anti-inflammatory program and render phagocytic cells unresponsive to a subsequent activation by a toll-like receptor (TLR) agonist. 2,3Accordingly, the presentation of particulate exogenous antigens by antigen-presenting cells (APCs) requires the presence of a TLR agonist within the phagocytosed cargo.

Ficolin-1–PTX3 Complex Formation Promotes Clearance of Altered Self-Cells and Modulates IL-8 Production

“…In disagreement with the previous reports by Gout et al (30), our results also revealed that removal of the terminal sialic acid moiety from the PTX3 pentraxin domain did not influence the ficolin-1-PTX3 interaction on dying host cells, thus lending further support to our perception that PTX3 interacts predominantly with ficolin-1 via its N-TD, but not the C-TD. The binding of complement proteins (e.g., ficolin-2 and ficolin-3) and PTX3 can enhance the uptake of apoptotic cells by phagocytes (16,17,31). Therefore, we analyzed the potential physiological implications of the ficolin-1-PTX3 cooperation on apoptotic cells in relation to phagocytosis.…”

“…Rabbit anti-ficolin-1 polyclonal Ab (pAb) was obtained from Hycult Biotechnology (HP9039; Uden, The Netherlands). Rabbit anti-PTX3 pAb with or without biotinylation, rat anti-PTX3 Nterminal domain (N-TD) mAb (MNB4), and rat anti-PTX3 C-terminal domain (C-TD) mAb (16B5) were characterized in our laboratories (31). HRP-conjugated donkey anti-rabbit IgG F(ab9) 2 and HRP-conjugated streptavidin were purchased from Amersham Biosciences (Hoersholm, Denmark).…”

HDL in Infectious Diseases and Sepsis

“…Surface bound CRP activates the classical pathway of complement through interaction with C1q, thus leading to cell elimination (Nauta et al 2003). Cell-bound PTX3 might favor the clearance of apoptotic cells (Jaillon et al 2009;Poon et al 2010) by enhancing the deposition of both C1q and C3 on cell surfaces (Nauta et al 2003). On the contrary, when in the fluid phase, PTX3 interacts with C1q and dampens the deposition on apoptotic cells and the resulting phagocytosis by dendritic cells and phagocytes (Baruah et al 2006;Gershov et al 2000;Rovere et al 2000;van Rossum et al 2004).…”

“…A specific binding has been observed to conidia of Aspergillus fumigatus (Garlanda et al 2002), Paracoccidioides brasiliensis, and zymosan (Diniz et al 2004), to selected Gram-positive and Gram-negative bacteria (Bozza et al 2006;Garlanda et al 2002;Jeannin et al 2005), and finally to some viral strains, including human and murine cytomegalovirus and influenza virus type A (IVA) (Bozza et al 2006;Reading et al 2008). Both short pentraxin and PTX3 bind apoptotic cells and facilitate their clearance (Doni et al 2012;Jaillon et al 2009). Surface bound CRP activates the classical pathway of complement through interaction with C1q, thus leading to cell elimination (Nauta et al 2003).…”

Innate recognition of apoptotic cells: novel apoptotic cell-associated molecular patterns revealed by crossreactivity of anti-LPS antibodies

“…1,[22][23][24][25][26] Nucleic acid 27 and a diverse range of proteins, including calreticulin, 28 the long pentraxin PTX3, 32 have also been shown to move to the surface of apoptotic cells from intracellular locations via as yet unknown mechanisms to facilitate phagocytic clearance. Recently in Drosophila, two proteins of the endoplasmic reticulum, Pretaporter and DmCaBP1, have been observed to become externalised in apoptosis aiding phagocytosis mediated by Draper, a fly hemocyte receptor for apoptotic cells that is homologous to CED-1.…”