The role of the cytoplasmic domain of human Fc gamma RII in cellular activation was studied by transfecting P815 cells with different isoforms or deletion mutants of this receptor and then assaying protein tyrosine phosphorylation after crosslinking with anti-CD32 monoclonal antibodies. Fc gamma RIIa, but not Fc gamma RIIb1 or b2, was able to trigger tyrosine phosphorylation. Deletion of just the carboxyl-terminal 19 amino acids of Fc gamma RIIa markedly reduced induction of protein tyrosine phosphorylation. Deletion of the carboxyl-terminal 38 amino acids of the cytoplasmic domain completely eliminated this response. These results indicate the cytoplasmic domain of human Fc gamma RIIa, the form of Fc gamma RII that predominates on human myeloid cells and platelets, contains sequences that allow activation of tyrosine phosphorylation; Fc gamma RIIb isoforms, the form of Fc gamma RII on human B lymphocytes, lack these sequences.
Amino Acid Sequence Animals