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Inhibitory signalling by the Fc receptor, FcgammaRIIB, proceeds without the involvement of the SH2-domain containing protein tyrosine phosphatase, SHP-1, in the mast cells. This results in the attachment of the SH2-domain containing inositol polyphosphate 5-phosphatase or SHIP to the tyrosine-phosphorylated 13-amino-acid of Fcgamma RIIB in both B-cells and mast cells. The hydrolysis of 5-phosphate of phosphatidylinositol/inositol gives a mechanism for the FcgammaRIIB inhibition of calcium influx triggered by immune receptors.

Weaknesses in the low-affinity immuno-globulin-G receptor Fc(gamma)RII or its signalling pathway in B cells upset the immune-complex-mediated feedback inhibition of the generation of antibodies. A study shows that the immunoglobulin levels of mice lacking in Fc(gamma)RII soar in reaction to antigens regardless of the latter's thymus-dependence. Findings indicate that Fc(gamma)RII negatively regulates immune-complex-triggered activation in vivo for the afferent as well as the efferent limbs of the immune reaction.

Author(s): Kyoko Shinya [1, 2, 4, 8]; Masahito Ebina [5]; Shinya Yamada [2]; Masao Ono [6]; Noriyuki Kasai [4]; Yoshihiro Kawaoka (corresponding author) [1, 2, 3, 7] Although more than [...]