DOCK8 Functions as an Adaptor that Links TLR–MyD88 Signaling to B Cell Activation

DOCK8 and MyD88 have been implicated in serologic memory. Here we report antibody responses were impaired and $CD27^+$ memory B cells were severely reduced in DOCK8-deficient patients. Toll-like receptor 9 (TLR9)- but not CD40-driven B cell proliferation and immunoglobulin production were severely reduced in DOCK8-deficient B cells. In contrast, TLR9-driven expression of AICDA, CD23 and CD86, and activation of NF-κB, p38 and Rac1 were intact. DOCK8 associated constitutively with MyD88 and the tyrosine kinase Pyk2 in normal B cells. Following TLR9 ligation, DOCK8 became tyrosine phosphorylated by Pyk2, bound the Src family kinase Lyn and linked TLR9 to a Src-Syk-STAT3 cascade essential for TLR9-driven B cell proliferation and differentiation. Thus, DOCK8 functions as an adaptor in a TLR9-MyD88 signaling pathway in B cells

DOCK8 functions as an adaptor that links TLR-MyD88 signaling to B cell activation

The adaptors DOCK8 and MyD88 have been linked to serological memory. Here we report that DOCK8-deficient patients had impaired antibody responses and considerably fewer CD27(+) memory B cells. B cell proliferation and immunoglobulin production driven by Toll-like receptor 9 (TLR9) were considerably lower in DOCK8-deficient B cells, but those driven by the costimulatory molecule CD40 were not. In contrast, TLR9-driven expression of AICDA (which encodes the cytidine deaminase AID), the immunoglobulin receptor CD23 and the costimulatory molecule CD86 and activation of the transcription factor NF-kappaB, the kinase p38 and the GTPase Rac1 were intact. DOCK8 associated constitutively with MyD88 and the tyrosine kinase Pyk2 in normal B cells. After ligation of TLR9, DOCK8 became tyrosine-phosphorylated by Pyk2, bound the Src-family kinase Lyn and linked TLR9 to a Src-kinase Syk-transcription factor STAT3 cascade essential for TLR9-driven B cell proliferation and differentiation. Thus, DOCK8 functions as an adaptor in a TLR9-MyD88 signaling pathway in B cells

The murine equivalent of the A181E TACI mutation associated with common variable immunodeficiency severely impairs B-cell function

TNFRSF13B, which encodes TACI (transmembrane activator and calcium-modulator and cyclophilin ligand interactor), is mutated in 10% of patients with common variable immune deficiency (CVID). One of the 2 most common TACI mutations in CVID, A181E, introduces a negative charge into the transmembrane domain. To define the consequence of the A181E mutation on TACI function, we studied the effect of its murine equivalent, mTACI A144E, on TACI signaling in transfected cells and on TACI function in transgenic mice. The mTACI A144E mutant, like its human TACI A181E counterpart, was expressed on the surface of 293T transfectants and was able to bind ligand, but exhibited impaired constitutive and ligand-induced NFκB signaling. In addition, constitutive and ligand-induced clustering of the intracellular domain was deficient for A144E as measured by fluorescence resonance energy transfer. Transgenic mice expressing the A144E mutant on TACI−/− background had low serum IgA levels and significantly impaired antibody responses to the type II T-independent antigen TNP-Ficoll. B cells from A144E transgenic mice were impaired in their capacity to proliferate and secrete IgG1 and IgA in response to TACI ligation. These results suggest that mTACI A144E mutation and its human counterpart, A181E, disrupt TACI signaling and impair TACI-dependent B-cell functions