Fc receptors of mouse cell lines. II. IgG binding specificity and identification of the Fc receptor on a lymphoid leukemia
Lane, B.C.; Bricker, M.D.; Cooper, S.M.
Journal of Immunology 128(4): 1825-1831
1982
ISSN/ISBN: 0022-1767 PMID: 6977571 Document Number: 185649
The binding specificity of the Fc receptors was determined on the murine lymphoid leukemia, L1210, which bears several surface antigens characteristic of B cells and B cell precursors. L1210 possesses an Fc receptor that binds monomer IgG of the IgG1, IgG2a and IgG2b subclasses with low affinity; aggregated IgG of these subclasses is bound comparatively well. There was no detectable binding of monomer or aggregated IgG3. Although direct binding of monomer IgG was difficult to demonstrate, monomer inhibition of aggregate binding was found at monomer concentrations > 0.2 mg/ml. There was cross-competition between monomers and aggregates of all 3 subclasses indicating that all were binding to the same Fc receptor. Isolation and characterization of the Fc receptor of L1210 was accomplished by affinity chromatography of the radiolabeled cell lysate over columns of Sepharose 4B coupled to various IgG and control proteins. A single protein, with an .apprx. MW of 60,000 (60 kd), was found to specifically bind to the Fc portion of IgG. This protein was demonstrated in the acetic acid and sodium dodecyl sulfate (SDS) eluates from columns coupled to monomer, aggregated or antigen-complexed IgG, but was not seen in eluates from F(ab')2 columns or from eluates of IgG columns that received the lysates of Fc receptor-negative cells. The 60 kd Fc binding protein was also demonstrated in the SDS eluates from affinity columns of Sepharose 4B coupled to myeloma proteins of mouse IgG1, IgG2a and IgG2b subclasses. In contrast to mouse macrophage-like cell lines that possess separate IgG subclass specific Fc receptors, L1210, a murine leukemia of possible B cell lineage, possesses a single Fc receptor with distinct binding and structural characteristics.