Williams Julie M, Ben-Smith Anne, Hewins Peter, Dove Stephen K, Hughes Philip, McEwan Robert, Wakelam Michael J O, Savage Caroline O S
Renal Immunobiology, MRC Centre for Immune Regulation, The Medical School, University of Birmingham, UK.
J Am Soc Nephrol. 2003 Mar;14(3):661-9. doi: 10.1097/01.asn.0000050223.34749.f4.
Anti-neutrophil cytoplasm autoantibodies (ANCA) are implicated in the pathogenesis of systemic vasculitis. Intact ANCA IgG activate superoxide generation in cytokine-primed neutrophils after binding their antigens and co-engaging Fcgamma receptors (FcgammaR). The contribution of antigen binding via ANCA F(ab')(2) fragments to signaling has been unclear. This study shows that both ANCA IgG and F(ab')(2) fragments of ANCA IgG induce significant GTPase activity, which could be blocked with pertussis toxin and anti-G(i) protein antibodies. Pertussis toxin inhibited ANCA IgG-induced superoxide generation but was without effect on superoxide production after conventional FcgammaR ligation. ANCA F(ab')(2) fragments did not induce superoxide generation. ANCA IgG activated PI 3-kinase-generating PIP(3), activated protein kinase B (PKB), and p21(ras); activation of each mediator was inhibited with pertussis toxin, but PI3K and PKB were not activated by ANCA IgG F(ab')(2) fragments. Intact ANCA IgG induced tyrosine phosphorylation, whereas F(ab')(2) fragments did not, and ANCA IgG-mediated superoxide generation was inhibited with genistein. Both genistein and pertussis toxin together completely abrogated the ANCA-induced oxidative burst. Genistein also inhibited ANCA IgG-induced PIP(3) generation and p21(ras) activation. These data implicate a novel ANCA IgG stimulated signaling pathway that involves both F(ab')(2)-mediated antigen binding and Fc-mediated FcgammaR ligation in cooperative interactions between G(i) proteins and tyrosine kinases that facilitates activation of downstream mediators.
抗中性粒细胞胞浆自身抗体（ANCA）与系统性血管炎的发病机制有关。完整的ANCA IgG在结合其抗原并共同激活Fcγ受体（FcγR）后，可在细胞因子预处理的中性粒细胞中激活超氧化物的产生。通过ANCA F(ab')(2)片段进行抗原结合对信号传导的作用尚不清楚。本研究表明，ANCA IgG及其F(ab')(2)片段均可诱导显著的GTP酶活性，该活性可被百日咳毒素和抗G(i)蛋白抗体阻断。百日咳毒素抑制ANCA IgG诱导的超氧化物产生，但对传统FcγR连接后的超氧化物产生无影响。ANCA F(ab')(2)片段不诱导超氧化物产生。ANCA IgG激活PI 3激酶产生PIP(3)，激活蛋白激酶B（PKB）和p21(ras)；每种介质的激活均被百日咳毒素抑制，但PI3K和PKB未被ANCA IgG F(ab')(2)片段激活。完整的ANCA IgG诱导酪氨酸磷酸化，而F(ab')(2)片段则不然，并且染料木黄酮可抑制ANCA IgG介导的超氧化物产生。染料木黄酮和百日咳毒素共同作用可完全消除ANCA诱导的氧化爆发。染料木黄酮还抑制ANCA IgG诱导的PIP(3)产生和p21(ras)激活。这些数据表明，一种新的ANCA IgG刺激的信号通路涉及F(ab')(2)介导的抗原结合和Fc介导的FcγR连接，在G(i)蛋白和酪氨酸激酶之间的协同相互作用中促进下游介质的激活。
