Superclustering of B cell receptor and Fc gamma RIIB1 activates Src homology 2-containing protein tyrosine phosphatase-1.

ABSTRACT

Fc gamma RIIB1 (CD32) is a receptor that binds the Fc domain of Ag-complexed IgG. Coaggregation of B cell receptor (BCR) and Fc gamma RIIB1 generates a dominant negative signal that inhibits B cell activation. In Ag-specific Id-positive B cells, the co-cross-linking of BCR and Fc gamma RIIB1 by anti-Id Ab resulted in the association of both Src homology 2-containing protein tyrosine phosphatase (SHP-1) and Src homology 2-containing inositol phosphatase (SHIP) with the Fc gamma RIIB1; however, only SHIP activity was detected. "Superclustering" of the BCR and Fc gamma RIIB1 complex induced by stimulation with anti-Id Ab plus polyvalent Ag synergistically activated SHP-1. The degree of co-cross-linking between BCR and Fc gamma RIIB1 may determine the activation status of SHP-1 and SHIP.