Structure and expression of Fc gamma receptors on mouse suppressor T cell hybridomas.

Antigen-specific and idiotype-specific mouse suppressor T cell hybridomas were analyzed for the presence and specificity of Fc gamma receptors (Fc gamma R) by EA rosetting and by flow microfluorometry with the use of monoclonal antibodies. We found that four hybridomas expressed Fc gamma R specific for IgG1 and IgG2b, one of which became Fc gamma R- during prolonged culture. Four other hybridomas and the fusion parent, BW5147, consistently lacked Fc gamma R. The 125I-labeled Fc gamma R were isolated from surface radioiodinated hybridoma cells solubilized with 1% Nonidet P-40, were purified by using single or repetitive chromatography on mouse IgG-Sepharose columns, and were analyzed by SDS-PAGE. An 125I-labeled 56,000 to 61,000 Mr macromolecule was isolated from each of the Fc gamma R+ hybridomas, but from none of the Fc gamma R- hybridomas nor from BW5147 cells. This macromolecule rebound to insolubilized mouse IgG1, IgG2b, and human Fc fragments, but not to insolubilized mouse IgG2a, IgG3, or IgA or human F(ab')2 fragments, consistent with the specificity observed for Fc gamma R on intact hybridoma cells. The mouse suppressor T cell Fc gamma R differs in size and specificity from mouse B cell Fc gamma R. A 70,000 Mr protein expressed on all hybridomas and on BW5147 cells was radiolabeled and, despite preclearing with ovalbumin-Sepharose, bound to the mouse IgG-Sepharose columns, presumably due to mouse antibodies to gp-70. This macromolecule was completely and specifically removed by using goat antiserum to gp-70.