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Ligand binding by the pl50,95 antigen of U937 monocytic cells: properties in common with complement receptor type 3 (CR3)
Author(s) -
Malhotra Vivek,
Hogg Nancy,
Sim Robert B.
Publication year - 1986
Publication title -
european journal of immunology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.272
H-Index - 201
eISSN - 1521-4141
pISSN - 0014-2980
DOI - 10.1002/eji.1830160915
Subject(s) - immunoprecipitation , biology , ic3b , microbiology and biotechnology , monoclonal antibody , g alpha subunit , protein subunit , antigen , u937 cell , sepharose , antibody , receptor , interleukin 10 receptor, alpha subunit , cell culture , biochemistry , immunology , genetics , gene , enzyme
Abstract U937 cells (a monocytic cell line) grown in the presence of phorbol myristate acetate were surface labeled with 125 I and the iC3b‐binding proteins isolated by affinity chromatography on iC3b‐Sepharose in the presence of divalent cations. Three polypeptides of 170, 150 and 95 kDa were found to bind specifically to iC3b‐Sepharose. The polypeptides of 170 and 95 kDa were identified as the α and the β subunits of CR3 by immunoprecipitation with OKM1 monoclonal antibody. The 150‐kDa polypeptide was not immunoprecipitated by antibodies to the α subunit of CR3 or LFA‐1. However, the 150‐kDa polypeptide, together with the 95‐kDa polypeptide, was immunoprecipitated with an anti‐β subunit‐specific antibody IB4, which immunoprecipitates LFA‐1, CR3 and pl50,95. These results indicated that the 150‐kDa polypeptide is the a subunit of the pl50,95 antigen. The binding of pl50,95 and CR3 to iC3b‐ Sepharose is specific as neither binds to C3u‐Sepharose. A monoclonal antibody, 3.9, which immunoprecipitated the 150 and a 95‐kDa polypeptide from U937 cells was characterized as being directed against the α‐subunit of the pl50,95 antigen. Phorbol myristate acetate‐stimulated U937 cells form rosettes with EAC3b and EAiC3b but not with EAC3d cells. Monoclonal antibody 3.9 does not inhibit either type of rosetting, but we were unable to exclude a role for pl50,95 in adherence of iC3b‐coated particles. Since there is no rosetting with C3d‐bearing particles it is unlikely that pl50,95 is a receptor for C3d, a role for pl50,95 which has been suggested by others (Wright, S. D., Licht, M. R. and Silverstein, S. C, Fed. Proc. 1984. 43 : 413).