Cain J A, Newman S L, Ross G D
Complement. 1987;4(2):75-86. doi: 10.1159/000463011.
Previous studies have suggested that neutrophil complement receptor type three (CR3) has two binding sites: (1) a site for fixed iC3b that does not trigger ingestion or a superoxide (O2-) burst, and (2) a function-triggering site for the beta-glucan component of yeast (Saccharomyces cerevisiae) cell walls. In the present study it was found that yeast (Y) coated with C3b (YC3b) or iC3b (YC3bi), prepared with purified complement in an IgG-free system, were avidly ingested ans stimulated a vigorous O2- burst, whereas sheep erythrocytes (E) bearing C3b or iC3b, were not ingested and did not give an O2- burst. YC3b and YC3bi contained an amount of fixed C3 that was approximately equal to serum-opsonized Y (OY), and produced O2- bursts comparable to OY. Experiments utilizing rabbit F(ab')2 anticomplement receptor type one (anti-CR1) to block fixed C3b binding to CR1, and monoclonal anti-CR3 (MN-41 or OKM1) to block fixed iC3b and Y cell wall binding to CR3, indicated that the O2- burst response to OY was primarily due to fixed iC3b and Y cell wall binding to CR3. Fixed C3b (that represented 33% of the fixed C3 on OY) and IgG anti-Y antibodies that bound to CR1 and Fc receptors, respectively, were found to contribute little to the response. Although YC3b did bind avidly to neutrophil CR1, the results suggested that the O2- burst response to YC3b was triggered after the initial YC3b binding by the secondary attachment of Y cell wall components to CR3. When neutrophils were treated with anti-CR3, 90% of neutrophils bound YC3b (via CR1), but phagocytosis and an O2- burst were completely absent. Similar findings were made with OKM1-treated neutrophils and YC3bi. Responses of OKM1-treated neutrophils were inhibited because only the iC3b-binding site of CR3 was ligated by the YC3bi. Thus, fixed C3b or iC3b on Y mediate avid binding of Y to neutrophils via CR1 or the iC3b-binding site of CR3, respectively, but ingestion and an O2- burst response are only triggered when glucans in the Y cell wall secondarily bind to neutrophils via the beta-glucan binding site of CR3.
先前的研究表明，中性粒细胞三型补体受体（CR3）有两个结合位点：（1）一个与固定的iC3b结合的位点，该位点不会引发吞噬作用或超氧化物（O2-）爆发；（2）一个与酵母（酿酒酵母）细胞壁的β-葡聚糖成分结合的功能触发位点。在本研究中发现，在无IgG系统中用纯化的补体制备的包被有C3b（YC3b）或iC3b（YC3bi）的酵母（Y），能被大量吞噬并刺激强烈的O2-爆发，而带有C3b或iC3b的绵羊红细胞（E）则不被吞噬且不产生O2-爆发。YC3b和YC3bi所含固定C3的量与血清调理的Y（OY）大致相等，并产生与OY相当的O2-爆发。利用兔F(ab')2抗一型补体受体（抗CR1）阻断固定的C3b与CR1的结合，以及单克隆抗CR3（MN-41或OKM1）阻断固定的iC3b和Y细胞壁与CR3的结合的实验表明，对OY的O2-爆发反应主要是由于固定的iC3b和Y细胞壁与CR3的结合。发现与CR1和Fc受体结合的固定C3b（占OY上固定C3的33%）和IgG抗Y抗体对该反应贡献很小。尽管YC3b确实能与中性粒细胞CR1紧密结合，但结果表明，对YC3b的O2-爆发反应是在YC3b最初结合后，由Y细胞壁成分与CR3的二次结合触发的。当中性粒细胞用抗CR3处理时，90%的中性粒细胞（通过CR1）结合YC3b，但吞噬作用和O2-爆发完全不存在。用OKM1处理的中性粒细胞和YC3bi也有类似的发现。用OKM1处理的中性粒细胞的反应受到抑制，因为只有CR3的iC3b结合位点被YC3bi连接。因此，Y上的固定C3b或iC3b分别通过CR1或CR3的iC3b结合位点介导Y与中性粒细胞的紧密结合，但只有当Y细胞壁中的葡聚糖通过CR3的β-葡聚糖结合位点与中性粒细胞二次结合时，才会触发吞噬作用和O2-爆发反应。
