The selective engulfment of apoptotic bodies by dendritic cells is mediated by the αvβ3 integrin and requires intracellular and extracellular calcium

Abstract

Dendritic cells derived in vitro from monocytes are known to be poor phagocytes. Here we show that, unlike macrophages, monocyte-derived dendritic cells indeed fail to take up opsonized particles or necrotic cells; however, apoptotic bodies are efficiently engulfed by dendritic cells. The temperature dependence and the sensitivity to cytochalasin D indicate that the apoptotic body engulfment is representative of early stages of phagocytosis. Inhibition studies with ligands for surface molecules involved in recognition of apoptotic bodies, such as vitronectin receptor, CD36 and phosphatidylserine receptor, revealed that apoptotic body engulfment by dendritic cells is mediated preferentially by the vitronectin receptor alpha(v)beta3, while all the receptors, with different efficiency, are engaged in phagocytosis of apoptotic bodies by macrophages. The interaction between apoptotic bodies and dendritic cells elicits a rise in intracellular free calcium concentration ([Ca2+]i) which is essential for the process of engulfment. Either intra- or extracellular Ca2+ buffering inhibits apoptotic body engulfment by dendritic cells and [Ca2+]i increases, indicating the involvement of both intra- and extracellular Ca2+. In contrast, Ca2+ mobilization is dispensable for macrophage phagocytosis of apoptotic bodies. The different requirements of Ca2+ in macrophages and dendritic cells is possibly due to the differential usage of phagocytic receptors (CD36 vs. alpha(v)beta3) and might reflect different fates of apoptotic bodies in the two cell types.

Apoptosis assays with lymphoma cell lines: problems and pitfalls

“…Sub-G 1 DNA content, assayed by staining with PI Necrotic cells were produced by two methods that have been used by others for this purpose: treatment with heat (Rubartelli et al, 1997) or the mild detergent digitonin (Single et al, 1998). They were also produced by freeze -thawing.…”

Nonphlogistic Clearance of Late Apoptotic Neutrophils by Macrophages: Efficient Phagocytosis Independent of β2 Integrins

“…Future work should take into account the possibility that clearance mechanisms dedicated to removal of late apoptotic cells could exist. Some support for this possibility can be drawn from the observation by Rubartelli et al that myeloid dendritic cells may use ␣ v integrins in selective ingestion of late apoptotic cells (26).…”

“…A number of different types of phagocytes can deploy the phagocyte surface ␣ v ␤ 3 vitronectin receptor integrin to present bridging thrombospondin 1 (TSP1) to apoptotic cells and promote phagocytosis without inciting proinflammatory secretory responses (10,11,23,24). This mechanism was a strong candidate for M recognition of late apoptotic neutrophils, because 1) these cells exhibit limited fusion with the plasma membrane of granules containing proteins capable of binding TSP1 (21,22,25); 2) a very recent report indicates that late apoptotic neutrophils bind TSP1 with such efficiency that this can be demonstrated with soluble biotinylated TSP1 (19); and 3) myeloid dendritic cells bind late apoptotic cells via an ␣ v -mediated mechanism (26). However, equally strong candidate phagocyte receptors were those of the ␤ 2 integrin family that bind opsonic complement fragments, type 3 complement receptor (CR3; ␣ m ␤ 2 or CD11b/CD18) and CR4 (␣ x ␤ 2 or CD11c/ CD18).…”

The consequences of apoptosis in autoimmunity

“…Albert et al reported that immature DC are capable of phagocytosis of apoptotic cells, although not as efficiently as macrophages [25,44] and that they can cross-present viral, tumor, and selfantigens to CD8+ T cells [45]. Moreover, it was recently suggested that apoptotic cells are able to promote maturation of DCs by upregulating costimulatory molecules and inducing proinflammatory cytokine release, while functioning as endogenous adjuvants for the induction of specific T cell responses [46].…”