CH3 domain of IgG as binding site to Fc receptor on mouse lymphocytes

MEMBRANE receptors recognising the Fc portion of immunoglobulin molecules (Fc receptors) are found in many cells of the immune system 1–4 . Fc receptors on lymphocytes are readily detected by a rosette test 3,5,6 and this reaction is inhibited by pretreatment of the lymphocytes with IgG (ref. 3). IgG proteins lacking almost the entire C H 1 and C H 3 homology regions have been obtained from mutant cell lines of MOPC 21, a plasmacytoma secreting IgG1 (refs 7 and 8) and the extent of the deletions determined (Fig. 1). To identify that part of the IgG molecule which interacts with the Fc receptor, we have tested the ability of these IgG proteins to inhibit Fc rosette formation on murine lymph node cells. We show (Table 1) that an intact C H 3 region is essential for the binding of IgG to Fc receptors on lymph node cells.