The regulation of membrane-bound and secreted immunoglobulins in the human lymphoid cell line LICR-LON and human hybridomas.
The synthesis of membrane-bound and secreted immunoglobulin was investigated in the human line LICR-LON-HMy2, a cell line often used for the derivation of human hybridomas. PAGE-SDS analysis of immunoprecipitates obtained from 35S-methionine labelled cell lysates shows that LICR-LON synthesize a hitherto undetected membrane form of IgG (with a heavy chain of mol. wt 62,000) in addition to the secretor form of IgG already described (55,000 heavy chain). Tunicamycin treatment, pulse-chase experiments and Western blot analysis showed that both chains are synthesized as independent proteins. Hybridomas obtained after fusion of LICR-LON and human peripheral blood lymphocytes retained the ability of the parental cell line to synthesize gamma m and gamma s. Some of these hybrids synthesize and secrete IgM which presumably originates from the parental B-lymphocytes. Precipitation and PAGE-SDS analysis of membrane proteins after iodination of intact cells revealed only one heavy chain band, corresponding in size to that of the gamma m. No indication of the synthesis of the membrane form of IgM was found in the hybrids. These data show that the parental (lymphoid) phenotype (m and s-IgG) is codominant with the more differentiated phenotype (s-IgM) of the fusion partner cell (plasma cell). These observations are compatible with a class-specific m-s regulation operating on a different chromatin structure at the expressed Ig loci of each parental chromosome.
Díaz-Espada
F
F
Department of Immunology, Clínica Puerta de Hierro, Madrid, Spain.
Milstein
C
C
Secher
D
D
D000912:Antibodies, Neoplasm / Q000096:biosynthesis*; D002460:Cell Line; D002462:Cell Membrane / Q000276:immunology; D002999:Clone Cells / Q000276:immunology; D004591:Electrophoresis, Polyacrylamide Gel; D005786:Gene Expression Regulation; D006031:Glycosylation; D006801:Humans; D006825:Hybridomas / Q000276:immunology; D007074:Immunoglobulin G / Q000096:biosynthesis*; D007938:Leukemia / Q000276:immunology*
D000912:Antibodies, Neoplasm; D007074:Immunoglobulin G