MacGlashan Donald W, Ishmael Susan, MacDonald Susan M, Langdon Jacqueline M, Arm Jonathan P, Sloane David E
Asthma and Allergy Center, Johns Hopkins University, Baltimore, MD 21224, USA.
J Immunol. 2008 Mar 15;180(6):4208-17. doi: 10.4049/jimmunol.180.6.4208.
In the general population, Syk expression in human basophils is highly variable and correlates well with the IgE-mediated responsiveness of these cells. Previous studies established that IgE-mediated stimulation results in loss of Syk expression. The current studies investigated whether stimulation through other receptors results in loss of Syk. Two classes of stimulation were examined, those that operate through the kinase Syk and those that operate through a GTP-binding protein. These studies demonstrated that aggregation of leukocyte Ig-like receptor LILRA-2 resulted in phosphorylation of Syk and c-Cbl, was inhibited by a third generation Syk inhibitor with an expected IC(50), and induced histamine release in strict proportion to release induced by anti-IgE Ab. Stimulation of LILRA-2 for 18 h resulted in modest loss of Syk that correlated with the more profound loss of Syk induced by anti-IgE Ab. Human recombinant histamine-releasing factor has also recently been shown to induce Syk phosphorylation and in the current studies has also been shown to induce loss of Syk in 18-h cultures. fMLP stimulation for 18 h was also found to induce modest loss of Syk. fMLP induced phosphorylation of c-Cbl that was sustained for at least 45 min. Phosphorylation of c-Cbl was inhibited by a Syk kinase inhibitor but with an IC(50) that was not consistent with Syk activity, suggesting another kinase was responsible for Cbl phosphorylation following fMLP. These studies demonstrate that it is possible to induce the loss of Syk expression in human basophils by a non-IgE-dependent mechanism and even by a mechanism that does directly involve Syk in the reaction complex.
在普通人群中，人类嗜碱性粒细胞中Syk的表达高度可变，且与这些细胞的IgE介导的反应性密切相关。先前的研究表明，IgE介导的刺激会导致Syk表达丧失。当前的研究调查了通过其他受体的刺激是否会导致Syk丧失。研究了两类刺激，一类通过激酶Syk起作用，另一类通过GTP结合蛋白起作用。这些研究表明，白细胞免疫球蛋白样受体LILRA-2的聚集导致Syk和c-Cbl磷酸化，被具有预期IC(50)的第三代Syk抑制剂抑制，并诱导组胺释放，其释放量与抗IgE抗体诱导的释放量严格成比例。刺激LILRA-2 18小时导致Syk适度丧失，这与抗IgE抗体诱导的Syk更显著丧失相关。人重组组胺释放因子最近也被证明可诱导Syk磷酸化，在当前研究中还表明其在18小时培养中可诱导Syk丧失。还发现fMLP刺激18小时也可诱导Syk适度丧失。fMLP诱导c-Cbl磷酸化，该磷酸化持续至少45分钟。c-Cbl的磷酸化被Syk激酶抑制剂抑制，但IC(50)与Syk活性不一致，表明在fMLP后另一种激酶负责Cbl磷酸化。这些研究表明，有可能通过非IgE依赖机制，甚至通过一种不直接涉及反应复合物中Syk的机制，诱导人类嗜碱性粒细胞中Syk表达丧失。
