Division of Drug Research, Department of Medical and Health Sciences, Linköping University, SE-58185 Linköping, Sweden.
Immunobiology. 2010 Dec;215(12):987-95. doi: 10.1016/j.imbio.2009.11.004. Epub 2010 Feb 16.
Blood platelets are emerging as important immunomodulatory cells, but complement interaction with platelets is not well understood. Several platelet structures have been described as complement protein 1q (C1q) binding receptors, such as C1qRp/CD93 and gC1qR. However, there are conflicting results whether these receptors are C1q binding structures, or even at all expressed on the cell surface. Recently, the collagen-binding integrin αIIβI was reported to bind C1q on mast cells, and this receptor is also present on platelets. The aim of this study was to further characterize the effects of C1q on platelets, by quantifying the platelet surface expression of P-selectin (CD62P) and monitoring the formation of platelet-neutrophil aggregates. Using flow cytometry, we found that C1q dose-dependently triggered a rapid but moderate and transient up-regulation of P-selectin already within 5s of C1q exposure. Pre-incubation with an antibody directed against gC1qR significantly inhibited (with 57% compared to control) the up-regulation, whereas an antibody towards the αIIβI-integrin showed no effect. Stimulation with C1q did not change the cytosolic calcium-levels, as measured with the fluorescent ratiometric probe Fura-2, however, a protein kinase C inhibitor (GF109203x) blocked the C1q-induced P-selectin expression. Furthermore, pre-incubation of platelets with C1q diminished both the collagen as well as the collagen-related peptide-induced up-regulation of P-selectin, most evident after 90s of stimulation. This indicates that C1q may regulate platelet activation via the GPVI receptor, which is a novel finding. Moreover, C1q antagonized the collagen-induced formation of platelet-neutrophil aggregates, indicating a reduced interaction between platelet P-selectin and neutrophil P-selectin glycoprotein ligand-1(PSGL-1/CD162). In summary, C1q induces a moderate rapid platelet P-selectin expression, modulates subsequent collagen and collagen-related peptide stimulation of platelets, and inhibits the formation of platelet-neutrophil aggregates. These immuno-regulatory effects of C1q may have a crucial role in innate immunity and inflammation.
血小板正在成为重要的免疫调节细胞，但补体与血小板的相互作用还没有被很好地理解。已经有几种血小板结构被描述为补体蛋白 1q（C1q）结合受体，例如 C1qRp/CD93 和 gC1qR。然而，这些受体是否是 C1q 结合结构，甚至是否在细胞表面表达，存在相互矛盾的结果。最近，胶原结合整合素αIIβI 被报道在肥大细胞上结合 C1q，而这个受体也存在于血小板上。本研究的目的是通过定量血小板表面 P-选择素（CD62P）的表达和监测血小板-中性粒细胞聚集体的形成，进一步研究 C1q 对血小板的影响。使用流式细胞术，我们发现 C1q 以剂量依赖的方式迅速但适度且短暂地触发 P-选择素的上调，在 C1q 暴露后的 5 秒内即可观察到。用针对 gC1qR 的抗体预先孵育可显著抑制（与对照相比抑制 57%）上调，而针对αIIβI 整合素的抗体则没有效果。用荧光比率探针 Fura-2 测量细胞内钙离子水平，发现 C1q 刺激不会改变细胞内钙离子水平，然而，蛋白激酶 C 抑制剂（GF109203x）阻断了 C1q 诱导的 P-选择素表达。此外，血小板与 C1q 预孵育可降低胶原和胶原相关肽诱导的 P-选择素的上调，在刺激 90 秒后最为明显。这表明 C1q 可能通过 GPVI 受体调节血小板激活，这是一个新的发现。此外，C1q 拮抗胶原诱导的血小板-中性粒细胞聚集体的形成，表明血小板 P-选择素和中性粒细胞 P-选择素糖蛋白配体-1（PSGL-1/CD162）之间的相互作用减少。综上所述，C1q 诱导血小板适度快速表达 P-选择素，调节随后胶原和胶原相关肽对血小板的刺激，并抑制血小板-中性粒细胞聚集体的形成。C1q 的这些免疫调节作用可能在先天免疫和炎症中起关键作用。
