The role of the mannose/N‐acetylglucosamine receptor in the pinocytosis of horseradish peroxidase by mouse peritoneal macrophages

Abstract

Saccharomyces cerevisiae mannan inhibits the pinocytosis of horseradish peroxidase (HRP) by resident, thioglycollate‐, proteose peptone‐, and Co‐rynebacterium parvum‐elicited macrophages from 30 to 70% when 1 mg/ml HRP is used, and 65 to 87% when 250 μg/ml HRP is used. In contrast, HRP uptake by J774 cells, a macrophage cell line reported to have little mannose receptor activity, is inhibited only about 25% by mannan. HRP uptake by resident and thioglycollate‐elicited (thio) macrophages is also inhibited 34 and 66% by addition of EGTA to the medium and 55 and 79% by trypsin treatment of the macrophages, respectively. The inhibitory effect of EGTA can be reversed by 1 mM excess Ca²⁺. High extracellular concentrations of Ca²⁺, in the range of 10–20 mM, however, inhibit pinocytosis in resident macrophages by about 50%. Sucrose uptake by resident macrophages is not appreciably affected by mannan. These results support the hypothesis that HRP uptake is mediated by the macrophage mannose/N‐acetylgluco‐samine receptor. PMA stimulates fluid‐phase pinocytosis of HRP by thio‐macrophages but does not affect receptor‐mediated uptake of HRP, while the combination of adenosine, homocysteine, and erythro‐9‐(2‐hydroxy‐3‐nonyl) adenine (EHNA) selectively inhibits bulk‐phase uptake by thio macrophages.