INTERFERON-GAMMA INHIBITS ENDOCYTOSIS OF SOLUBLE AMINATED BETA-1,3-D-GLUCAN AND NEUTRAL RED IN MOUSE PERITONEAL-MACROPHAGES

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 t he macrophages are treated with IFN-gamma, Because our data indicated that AG is taken up by macrophages through beta-glucan receptor-mediat ed endocytosis, we wanted to characterize further the inhibitory effec t of IFN-gamma on endocytosis, We compared the internalization of AG a nd neutral red (NR). NR is internalized by macrophages through fluid-p hase endocytosis, AG and NR showed a similar influx/efflux pattern, Th e initial rate of accumulation was much larger for AG than for NR, how ever, 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 las er scanning microscopy (CLSM) images, Both the influx and effux of AG and NR was inhibited by treatment of macrophages with IFN-gamma, Phorb ol myristate acetate (PMA) added to the cell cultures increased the ac cumulation of AG and NR and reversed the inhibitory effect of IFN-gamm a, The effect of PMA was dependent on functionally intact microfilamen ts and microtubules, CLSM showed that the accumulated AG was localized mostly in small vesicles (size < 2 mu m) in IFN-gamma-treated cells, in large and small vesicles in untreated cells, and mostly in large ve sicles (size > 2 mu m) 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 formatio n of large vesicles.