DISTRIBUTION, INDUCIBILITY AND BIOLOGICAL FUNCTION OF THE CLONED AND EXPRESSED HUMAN BETA-FC RECEPTOR-II

A cDNA encoding the human βFcγ receptor II (FcRII) was isolated from a placental cDNA library. Analysis of the predicted amino acid sequence indicates that this receptor is synthesized with a 42‐amino acid leader sequence. The mature protein consists of 249 amino acids. The leader sequence and the cytoplasmic domain are strikingly different from the CDw32 antigen but show great homology to the mouse β2FcR. RNA blot analysis of human cells using CDw32 and βFcRII‐specific DNA fragments demonstrated one βFcRII transcript (1.7 kb) in B cells and in HL‐60 cells which were induced to differentiate along a monocyte‐macrophage pathway by phorbol 12‐myristate 13‐acetate treatment. Under these conditions the CDw32 transcripts (2.5 and 1.7 kb) are induced to a minor extent in HL‐60 cells. In contrast, the 2.5‐kb CDw32 transcript is strongly induced in HL‐60 cells which have been induced to differentiate into granulocytes by exposure to dimethylsulfoxide. To determine the biological properties of the βFcRII, we expressed the antigen in FcR− hamster cells. Only immune complexes but not monomeric human IgG were bound significantly. Bound ligand was efficiently internalized within 15 min and it was then found in vesicular structures. Thus the low‐affinity βFcRII is able to internalize ligands without cooperation with any other FcR. Copyright © 1990 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim