Specificity of Fc receptors of activated T cells. Relation with released immunoglobulin‐binding factor

Abstract

Abstract This paper deals with the specificity of the receptor for immunoglobulins expressed on activated T cells (ATC) and its relation to immunoglobulin‐binding factor (IBF) produced in vitro by ATC. By indirect immunofluorescence and rosette techniques, it is shown that Fc receptors are expressed on a subpopulation of cells and are not species specific. Using inhibition techniques, we show (a) that rabbit or human IgG compete with mouse IgG for the fixation on the Fc receptor of mouse ATC, and (b) that the receptor is specific for the C‐terminal portion of the Fc fragment. These properties are shared by IBF. Moreover, incubation of ATC at 37°C provokes a decrease in Fc receptor positive cells and an increase in production of IBF into the supernatant. Both events are blocked by inhibitors of protein synthesis. In addition, degalan beads coated with IgG‐anti‐IgG complexes retain both IBF‐producing cells and Fc receptor‐bearing cells. These data suggest a relationship between the expression of Fc receptors at the surface of ATC and the release of IBF.