Lantz M, Björnberg F, Olsson I, Richter J
Department of Medicine University Hospital, Lund, Sweden.
J Immunol. 1994 Feb 1;152(3):1362-9.
TNF is a potent activator of neutrophil granulocytes which acts via two cell surface receptors: the p55-TNF receptor (TNF-R55) and the p75-TNF receptor (TNF-R75). The extracellular region of the receptors can be released by proteolytic cleavage and form soluble TNF-binding proteins, TNF-R55-BP and TNF-R75-BP, respectively. The phorbol ester PMA, the chemotactic peptide FMLP, and TNF were all found to induce release of TNF-R55-BP and TNF-R75-BP from neutrophils in suspension in a time- and dose-dependent manner as measured by ELISA. Exposure of neutrophils to 10 ng/ml of PMA for 60 min resulted in release of 900 pg of TNF-R55-BP and 350 pg of TNF-R75-BP per 5 million cells, corresponding to approximately 4800 receptors per cell. In addition, adherence by itself of neutrophils to fibrinogen-coated culture plates and other surfaces resulted in a release of TNF-R55-BP of the same magnitude as seen in response of neutrophils in suspension to 1 nM TNF, whereas the release of TNF-R75-BP was less pronounced. The protein kinase C inhibitors staurosporin and calphostin C inhibited both the TNF-, PMA-, and adherence-induced release of soluble forms of TNFRs. Ab to the common beta-chain of the leukocyte integrins (CD18) did not affect adherence-induced TNF-R55-BP release, indicating that non-integrin-dependent mechanisms are involved in receptor cleavage. However, cross-linking of anti-CD18 Ab (IB4) with a Fab2 fragment resulted in a decrease of specific binding of 125I-TNF to neutrophils indicating that the leukocyte integrins can modulate TNFR expression on neutrophils. Thus, adherence to a biological surface, without additional stimuli, induces release of soluble TNFR form from neutrophils. TNFR expression can be modulated by protein kinase C as well as both leukocyte integrins and non-integrin-dependent adherence mechanisms.
肿瘤坏死因子（TNF）是中性粒细胞的一种强效激活剂，它通过两种细胞表面受体发挥作用：p55-TNF受体（TNF-R55）和p75-TNF受体（TNF-R75）。受体的细胞外区域可通过蛋白水解切割而释放，分别形成可溶性TNF结合蛋白TNF-R55-BP和TNF-R75-BP。佛波酯PMA、趋化肽FMLP和TNF均被发现能以时间和剂量依赖的方式，诱导悬浮的中性粒细胞释放TNF-R55-BP和TNF-R75-BP，这是通过酶联免疫吸附测定法（ELISA）测量的。将中性粒细胞暴露于10 ng/ml的PMA中60分钟，每500万个细胞释放900 pg的TNF-R55-BP和350 pg的TNF-R75-BP，相当于每个细胞约4800个受体。此外，中性粒细胞自身黏附于纤维蛋白原包被的培养板和其他表面，会导致TNF-R55-BP的释放量与悬浮的中性粒细胞对1 nM TNF的反应中所见的释放量相当，而TNF-R75-BP的释放则不太明显。蛋白激酶C抑制剂星形孢菌素和钙磷蛋白C抑制了TNF、PMA和黏附诱导的可溶性TNFR形式的释放。针对白细胞整合素共同β链（CD18）的抗体不影响黏附诱导的TNF-R55-BP释放，表明非整合素依赖性机制参与受体切割。然而，抗CD18抗体（IB4）与Fab2片段交联导致125I-TNF与中性粒细胞的特异性结合减少，表明白细胞整合素可调节中性粒细胞上TNFR的表达。因此，在没有额外刺激的情况下，黏附于生物表面会诱导中性粒细胞释放可溶性TNFR形式。TNFR表达可由蛋白激酶C以及白细胞整合素和非整合素依赖性黏附机制调节。
