Properties of an Fc gamma-binding protein isolated from human leukemic B cells.

Abstract

A selectively Fc gamma-binding protein was isolated from purified and radioiodinated cell membranes from two cases of B-type chronic lymphocytic leukemia and one case of B-type prolymphocytic leukemia by binding to IgG aggregates, horseradish peroxidase-anti-peroxidase IgG complexes, and sheep erythrocyte membrane sheets densely coated with IgG. This protein could not be isolated from the cell membranes of an Fc gamma-receptor-negative chronic lymphocytic leukemia of the T type or from membranes of human erythrocytes. The Fc gamma-binding protein was efficiently solubilized by a mixture of Na-EDTA and 2-mercaptoethanol, but not with one of these agents alone, indicating that both divalent cations and disulfide bridges are involved in the linkage of the Fc gamma-binding protein to the cell membrane. In sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the Fc gamma-binding protein revealed an apparent mol wt of 28,000 and in isoelectric focusing it showed an isoelectric point of 5.5. The electrophoretic mobility of the 28,000-dalton protein did not change after reduction and alkylation. It was determined that the NH2-terminal amino acid of the protein was glycine. The isolated protein was unable to agglutinate antibody-coated erythrocytes. These findings suggest that the 28,000-dalton IgG-affined protein was composed to O2-enriched buffer lacking reducing agents, the 28,000-dalton protein aggregated to a 115,000-dalton molecule. The isolated Fc gamma-binding protein proved to be different from C1q or its subunits.

Isolation and partial characterization of Fc gamma-binding proteins of human leukocytes.

“…We have not isolated macromolecules smaller than 33,000 daltons as reported in previous studies with mononuclear cells of normal donors (24) and chronic lymphocytic leukemia patients (26,27). We suspect that the previous studies may have proteolytically degraded that Fc, receptor because cell lysates were incubated at 37°C (24,26) or were subjected to freezing and thawing and overnight dialysis (27).…”

“…We suspect that the previous studies may have proteolytically degraded that Fc, receptor because cell lysates were incubated at 37°C (24,26) or were subjected to freezing and thawing and overnight dialysis (27).…”

“…One group has isolated both 120,000-and 60,000-mol wt Fc.,-binding proteins from normal human mononuclear cells (24) and human T lymphocytes (25). But in other studies 28,000-or 30,000-mol wt Fc,-binding proteins were purified from patients with chronic lymphocytic leukemia (26,27).…”

Affinity Chromatography and SDS-PAGE Studies of Radiolabeled IgE-Binding and IgG-Binding Factors Generated from Human Lymphoblastoid Cell Lines

“…Normal T lymphocytes were reported to have Fc>,R proteins with MWs of 60,000 and 120,000 daltons under re duced and non-reduced conditions [5], whereas the KE 37 T cell line had FcySBM with MWs of 45,000 and 22,000 daltons under non-reduced and reduced conditions [2]. FcrR from human B cells have been reported with MWs of 30,000 [32], 46,000 [33] and 28.000 daltons, which was polymerized to a 120,000-dalton complex [35]. Fc,R proteins isolated from human lymphoblastoid B cells or the human monocyte cell line of U 937 have revealed MWs of 23,000, 46,000 and 86,000 daltons which aggregated to 125,000-250,000-daltons complexes [21,22], Also, the rabbit yolk sac membrane FcxR activity has been demonstrated in complexes having MWs of 225,000, 215.000 and 116,000 daltons [ 18].…”

Two neoplastic cell lines with unique features derived from Hodgkin's disease

“…Rosette assays to demonstrate C3b and C3d receptors (EAC rosette assays), IgG-receptors, mouse E and sheep E receptors were performed as described elsewhere (Stein et al, 1978b;Thoenes and Stein, 1979;Tolksdorf et al, 1980). T-cell rosette assay.…”