Tosi M F, Berger M
Department of Pediatrics, Case Western Reserve University School of Medicine, Cleveland, OH 44106.
J Immunol. 1988 Sep 15;141(6):2097-103.
Most previous studies of IgG FcR on neutrophils (PMN) have focused on a single FcR of Mr = 50 to 70 kDa, which is recognized by mAb 3G8 and anti-Leu-11a. In the course of studying the effects of extracellular proteases on PMN receptor expression and function, we found that treatment with human leukocyte elastase reduced the expression of this FcR on the PMN surface by as much as 85% in flow cytometric studies, but did not inhibit ingestion of IgG-coated particles or O2- production induced by multivalent IgG complexes, and caused only a 35% decrease in IC binding to PMN. Since a second FcR with Mr = 40 kDa recognized by mAb IV-3, recently has been identified on PMN, we sought to determine if this FcR was resistant to elastase and thus accounted for the elastase stability of IgG-mediated PMN functions. Elastase treatment that reduced 3G8 binding by 85% caused no decrease in binding of mAb IV-3. For non-elastase-treated PMN, mAb IV-3 against the 40 kDa FcR caused as much as 79 +/- 7% inhibition of IgG-induced O2- production, whereas mAb 3G8 against the 50 to 70 kDa FcR caused only 32 +/- 5% inhibition. In contrast, for IC-binding, mAb IV-3 caused only 15 +/- 6% inhibition, whereas mAb 3G8 caused as much as 80 +/- 9% inhibition, a reversal of their relative effects on O2- production. In parallel studies with elastase-treated PMN, mAb IV-3 actually blocked more IC binding than did mAb 3G8, 55 +/- 4% vs 40 +/- 6%, respectively, presumably because most of the 50 to 70 kDa FcR molecules had been cleaved. The effect of the two mAb together in blocking IC binding was additive, whereas for blocking of O2- production, mAb 3G8 added little or nothing to the effect of mAb IV-3 alone. Direct 125I-labeled Ab binding studies with intact PMN revealed seven times as many 50 to 70 kDa as 40kDa FcR, 110,200 +/- 9600 and 15,100 +/- 700 sites/cell, respectively. Our findings suggest that the elastase-resistant 40 kDa FcR is primarily responsible for IgG-mediated activation of human PMN, whereas the elastase-sensitive 50 to 70 kDa FcR predominates in IC binding, by virtue of its numerical superiority, but does not directly activate the cell. The latter may serve to hold IgG-coated microorganisms or other multivalent IC in place at the PMN surface, enhancing contact with the 40 kDa FcR and thus facilitating cell activation in a cooperative manner.
以往大多数关于中性粒细胞（PMN）上IgG Fc受体的研究都集中在一种分子量为50至70 kDa的单一Fc受体上，该受体可被单克隆抗体3G8和抗Leu - 11a识别。在研究细胞外蛋白酶对PMN受体表达和功能的影响过程中，我们发现，在流式细胞术研究中，用人白细胞弹性蛋白酶处理可使该Fc受体在PMN表面的表达降低多达85%，但不抑制对IgG包被颗粒的摄取或多价IgG复合物诱导的O₂⁻产生，且仅使免疫复合物（IC）与PMN的结合减少35%。由于最近在PMN上已鉴定出另一种可被单克隆抗体IV - 3识别的分子量为40 kDa的Fc受体，我们试图确定该Fc受体是否对弹性蛋白酶具有抗性，从而解释IgG介导的PMN功能的弹性蛋白酶稳定性。使3G8结合减少85%的弹性蛋白酶处理并未使单克隆抗体IV - 3的结合减少。对于未用弹性蛋白酶处理的PMN，针对40 kDa Fc受体的单克隆抗体IV - 3可使IgG诱导的O₂⁻产生受到多达79±7%的抑制，而针对50至70 kDa Fc受体的单克隆抗体3G8仅引起32±5%的抑制。相反，对于IC结合，单克隆抗体IV - 3仅引起15±6%的抑制，而单克隆抗体3G8则引起多达80±9%的抑制，它们对O₂⁻产生的相对作用发生了逆转。在对用弹性蛋白酶处理的PMN的平行研究中，单克隆抗体IV - 3实际上比单克隆抗体3G8阻断了更多的IC结合，分别为55±4%和40±6%，推测是因为大多数50至70 kDa的Fc受体分子已被裂解。两种单克隆抗体共同阻断IC结合的作用是相加的，而对于阻断O₂⁻产生，单克隆抗体3G8对单克隆抗体IV - 3单独作用的影响很小或没有影响。用完整的PMN进行的直接¹²⁵I标记抗体结合研究显示，50至70 kDa的Fc受体数量是40 kDa Fc受体的7倍，分别为110200±9600和15100±700个位点/细胞。我们的研究结果表明，对弹性蛋白酶具有抗性的40 kDa Fc受体主要负责IgG介导的人PMN的激活，而对弹性蛋白酶敏感的50至70 kDa Fc受体因其数量优势在IC结合中占主导地位，但不直接激活细胞。后者可能有助于将IgG包被的微生物或其他多价IC固定在PMN表面，增强与40 kDa Fc受体的接触，从而以协同方式促进细胞激活。
