Differential endocytotic characteristics of a novel human B/DC cell line HBM‐Noda: effective macropinocytic and phagocytic function rather than scavenging function

Abstract

SUMMARYIn order to characterize a novel human B cell-lineage dendritic cell line (B/DC line) as an antigenpresenting cell (APC), we compared three types of endocytosis (micropinocytosis via a clathrincoated pit, macropinocytosis via membrane ruf¯ing, and phagocytosis) among myeloid-related, macrophage (Mw) cell lines and a B/DC line. In the present examination, we used a unique human dendritic cell (DC) line, HBM-Noda (Noda). Flow cytometric and immunocytochemical analyses revealed that Noda not only expresses some DC markers, but also it expresses some B-cell associated markers. Noda shows strong capacities to stimulate allogenic T cells, to produce immunoglobulin G (IgG), and to perform immunoglobulin gene rearrangment. These data strongly suggest that Noda is a B-cell lineage DC line. The endocytic differences among these cell lines were as follows. (1) The level of micropinocytosis of Noda was signi®cantly less than that of conventional human Mw cell lines, and the formation of a clathrin-coated pit was not observed in Noda. (2) The level of macropinocytosis of Noda was also smaller than that of conventional Mw cells indicating that the active membrane ruf¯ing of Noda induces rapid recycling. (3) Phagocytosis of opsonized sheep red blood cells (SRBC) was performed more ef®ciently in Noda than in other Mw cell lines. Collectively, these data suggest that in human bone marrow cells, we can identify a unique DC subtype, B/DC line, which develops through a lymphoid DC-differentiation pathway, and DC in this lineage plays an important role in the host immune response because of its effective uptake of a variety of size of antigens by using the skilful membrane ruf¯ing and surface receptors

Macrophages use different internalization mechanisms to clear apoptotic and necrotic cells

“…It was recently proposed that formation of the ruffles is a specific feature of macropinocytosis. 36 Our SEM data revealed distinct surface features of macrophages: apoptotic target cells induce narrow pseudopods, whereas necrotic target cells induce broad membrane ruffles that are disproportional to the engulfed necrotic material.…”

Mechanisms of internalization of apoptotic and necrotic L929 cells by a macrophage cell line studied by electron microscopy

“…3A-C). The formation of membrane ruffles was proposed recently to be a specific feature of macropinocytosis, a type of endocytosis (Ridley et al, 1992;Lamaze and Schmid, 1995;Toril et al, 2001). Macropinosomes are classified as phase-bright organelles with diameters Ͼ0.2 m (Jones and Willingham, 1999).…”

“…One is the efficient antigen uptake mechanism involving the internalization of large particles called phagocytosis and the other is fluid phase uptake of small molecules. Fluid phase uptake can be performed via two distinct mechanisms, either by micropinocytosis, which is the ingestion of small vesicles via clathrin-coated pits or macropinocytosis by pinosomes (Ͼ0.2 m diameter), which are formed by membrane ruffling (Swanson and Baer, 1995;Swan-Figure 1 son and Watts, 1995;Akari et al, 1996;Jones and Willingham, 1999;Somersan and Bhardwaj, 2001;Toril et al, 2001).…”

Clearance of apoptotic and necrotic cells and its immunological consequences

“…In another form of phagocytosis, bacteria release protein messengers into the cytosol of the targeted host cells, causing cell surface ruffling and formation of macropinosome-like membrane invaginations [90]. These membrane invaginations form "spacious macropinosomes," wherein large amounts of external solute are internalized together with the bacterium [82,83,91]. Though several mechanisms for internalizing microorganisms have been proposed [92,93], information on the internalization mechanisms for apoptotic and necrotic cells is sparse.…”