Interferon-γ Inhibits Endocytosis of Soluble Aminated β-l,3-D-Glucan and Neutral Red in Mouse Peritoneal Macrophages

Abstract

We previously demonstrated that soluble animated beta-1,3-D-glucan (AG) is internalized after binding to a specific beta-glucan receptor on macrophages. Internalization, but not binding, of AG is reduced when the macrophages are treated with IFN-gamma. Because our data indicated that AG is taken up by macrophages through beta-glucan receptor-mediated endocytosis, we wanted to characterize further the inhibitory effect of IFN-gamma on endocytosis. We compared the internalization of AG and neutral red (NR). NR is internalized by macrophages through fluid-phase endocytosis. AG and NR showed a similar influx/efflux pattern. The initial rate of accumulation was much larger for AG than for NR, however, probably because of the involvement of the beta-glucan receptor in the uptake of AG. Internalized AG was associated with membranes of the endocytic vesicles and formed characteristic rings on confocal laser scanning microscopy (CLSM) images. Both the influx and efflux of AG and NR was inhibited by treatment of macrophages with IFN-gamma. Phorbol myristate acetate (PMA) added to the cell cultures increased the accumulation of AG and NR and reversed the inhibitory effect of IFN-gamma. The effect of PMA was dependent on functionally intact microfilaments and microtubules. CLSM showed that the accumulated AG was localized mostly in small vesicles (size < 2 microns) in IFN-gamma-treated cells, in large and small vesicles in untreated cells, and mostly in large vesicles (size > 2 microns) in PMA-treated cells. In conclusion, IFN-gamma inhibits both the beta-glucan receptor-mediated endocytosis of AG and the fluid-phase endocytosis of NR, probably by inhibiting the formation of large vesicles.

Functional characterization of mannose receptor expressed by immunocompetent mouse microglia

“…Interferons have long been known to interfere negatively with the pinocytosis capacity of macrophages by inducing changes in the cytoskeletal organization (Wang et al, 1984). Fluid‐phase pinocytosis (Konopski et al, 1995; Montaner et al, 1999), and pinocytosis mediated by the β‐glucan receptor (Konopski et al, 1995), the scavenger receptor (Geng and Hansson, 1992), as well as the mannose receptor (Stein et al, 1992; Montaner et al, 1999), are equally affected by IFNγ. We similarly observed a strong inhibition of the pinocytic capacity of microglia upon IFNγ treatment for 1 to 3 days (Fig.…”

Orally and Topically AdministeredSparassis crispa(Hanabiratake) Improved Healing of Skin Wounds in Mice with Streptozotocin-Induced Diabetes

“…[18][19][20][21][22][23] When a specific -glucan binds to its cognate receptor, it is rapidly internalized into macrophages, stimulating the transcription of cytokines that have functional roles in fibroblast migration and activation. [24][25][26] In addition to macrophages, normal human dermal fibroblasts also express at least two -glucan binding sites. Activation of -glucan receptors can modulate the functional activity of the cell by increasing nuclear factor (NF)-B signaling and the subsequent transcription of interleukin (IL)-6 mRNA.…”

Phagocytic Clearance of Apoptotic Neurons by Microglia/Brain Macrophages In Vitro

“…To test whether candidate inhibitors of microglial uptake of apoptotic neurons exert a nonspecific toxic effect upon the microglia, a viability assay was performed with neutral red in the presence of the agents used to interfere with the phagocytosis. Neutral red is internalized through fluid‐phase endocytosis (Konopski et al, 1995). Concentrations of monosaccharides, peptides, and OPS that were effective to inhibit uptake of apoptotic cells were not toxic to microglia (Table 1).…”