Chapman H A, Stone O L
J Clin Invest. 1984 Nov;74(5):1693-700. doi: 10.1172/JCI111586.
Elastin is an extracellular matrix protein critical to the normal structure and function of human lung. Recently reported data indicate that live human alveolar macrophages can degrade purified elastin in vitro. In this study, we directly compared the elastolytic activity of alveolar macrophages with that of human neutrophils. In the absence of proteinase inhibitors, human neutrophils degrade much more elastin than do human alveolar macrophages. However, macrophages cultured in 10% human serum and in contact with purified 3H-elastin degraded 4.7 micrograms elastin/10(6) cells per 24 h, as compared to less than 1 microgram/10(6) cells/24 h for neutrophils. We observed a similar pattern when the two cells were cultured in human alveolar fluid. We determined that the relative resistance of macrophage elastolytic activity to serum or alveolar proteinase inhibitors was not simply due to phagocytosis of substrate by the larger macrophages. Live macrophages as well as neutrophils degrade 125I-elastin coupled to noningestible sepharose beads. Again in serum-free media, neutrophils degraded eight-fold more elastin than macrophages but only macrophages degraded sepharose-coupled elastin in the presence of 10% serum. Because of these findings, we compared the enzymatic mechanisms of elastin breakdown by macrophages with that of neutrophils. Macrophage elastolytic activity is largely (65-80%) due to a cysteine proteinase(s), at least part of which is Cathepsin B. Approximately half of the cysteine proteinase activity appeared to be expressed at or near the cell surface. These experiments defined two enzymatically distinct pathways of elastin breakdown by human inflammatory cells: the classic, neutrophil derived soluble elastase(s) that is sensitive to serum and alveolar proteinase inhibitors, and a macrophage-mediated pathway that is largely cell associated and relatively resistant to inhibitors. The function of the two pathways depends on the relative excess or deficiency of soluble inhibitors. At inflammatory sites rich in proteinase inhibitors, tissue macrophages may degrade more extracellular matrix elastin than neutrophils. In smokers without antiproteinase deficiency, pulmonary macrophages, which are known to be increased in number, may be the more important cause of elastin breakdown and emphysema.
弹性蛋白是一种细胞外基质蛋白，对人类肺脏的正常结构和功能至关重要。最近报道的数据表明，活的人类肺泡巨噬细胞能够在体外降解纯化的弹性蛋白。在本研究中，我们直接比较了肺泡巨噬细胞与人中性粒细胞的弹性蛋白酶活性。在不存在蛋白酶抑制剂的情况下，人中性粒细胞比人肺泡巨噬细胞降解的弹性蛋白多得多。然而，在10%人血清中培养并与纯化的3H-弹性蛋白接触的巨噬细胞，每24小时每10⁶个细胞降解4.7微克弹性蛋白，而中性粒细胞每24小时每10⁶个细胞降解少于1微克。当将这两种细胞在人肺泡液中培养时，我们观察到了类似的模式。我们确定，巨噬细胞弹性蛋白酶活性对血清或肺泡蛋白酶抑制剂的相对抗性并非仅仅是由于较大的巨噬细胞对底物的吞噬作用。活的巨噬细胞以及中性粒细胞都会降解与不可吞噬的琼脂糖珠偶联的¹²⁵I-弹性蛋白。同样在无血清培养基中，中性粒细胞降解的弹性蛋白比巨噬细胞多八倍，但只有巨噬细胞在存在10%血清的情况下能降解与琼脂糖偶联的弹性蛋白。基于这些发现，我们比较了巨噬细胞与中性粒细胞分解弹性蛋白的酶促机制。巨噬细胞的弹性蛋白酶活性很大程度上（65 - 80%）归因于一种半胱氨酸蛋白酶，其中至少部分是组织蛋白酶B。大约一半的半胱氨酸蛋白酶活性似乎在细胞表面或其附近表达。这些实验确定了人类炎症细胞分解弹性蛋白的两种酶促不同途径：经典的、源自中性粒细胞的可溶性弹性蛋白酶，它对血清和肺泡蛋白酶抑制剂敏感，以及巨噬细胞介导的途径，该途径主要与细胞相关且对抑制剂相对抗性。这两种途径的功能取决于可溶性抑制剂的相对过量或不足。在富含蛋白酶抑制剂的炎症部位，组织巨噬细胞可能比中性粒细胞降解更多的细胞外基质弹性蛋白。在没有抗蛋白酶缺乏的吸烟者中，已知数量增加的肺巨噬细胞可能是弹性蛋白分解和肺气肿的更重要原因。
