Regulation of tyrosine-containing activation motif-dependent cell signalling by Fc gamma RII.

Crosslinking of the B-cell receptor (BCR) for antigen to low-affinity receptors for IgG (Fc gamma RII) inhibits B-cell activation induced by BCR aggregation. The cell-triggering properties of the BCR depend on tyrosine-containing activation motifs (TAM), in the intracytoplasmic domain of its Ig alpha and Ig beta subunits. TAMs also account for the cell-triggering capabilities of the T-cell receptor (TCR) for antigen, in T lymphocytes, and of the high-affinity receptor for IgE (Fc epsilon RI), in mast cells. Using as a model, rat basophilic leukemia cells (RBL-2H3) stably transfected with cDNA encoding wild-type or mutated murine or human Fc gamma RIIB and chimeric molecules having the intracytoplasmic domain of the FcR gamma subunit or of TCR-CD3 zeta subunit, we found that the inhibitory properties of Fc gamma RII are neither restricted to B cells nor to BCR-dependent cell activation, but can be extended to other cells and, as a general rule, to TAM-dependent cell activation.