Pneumocyte-Derived Host Defence Lectins

表面活性蛋白D（SurfactantProteinD，SP-D）在抵抗吸入性微生物、参与肺对抗原攻击的应答以及参与调节表面活性物质脂质稳态等方面发挥重要作用。SP-D可直接与中性粒细胞相互作用，并可在体外调节中性粒细胞的抗病毒、抗细菌和抗真菌功能。然而，也有证据表明，在急性肺损伤的情况下，中性粒细胞有助于SP-D的降解和清除，这表明中性粒细胞和SP-D在体内存在复杂的相互作用。我们最近观察到SP-D被三种主要的人中性粒细胞丝氨酸蛋白酶特异性降解：中性粒细胞弹性蛋白酶（NE）、组织蛋白酶G（CG）和蛋白酶3（PR 3），释放出类似的高分子量二硫键交联片段;类似的裂解由鼠中性粒细胞和整个中性粒细胞裂解物介导。鉴于上述情况，我们假设 嗜中性粒细胞衍生的蛋白酶特异性降解功能重要的凝集素结构域内的SP-D。我们进一步假设，中性粒细胞丝氨酸蛋白酶有助于增强清除的SP-D在设置的LPS挑战，从而有助于消耗的功能形式的宿主防御蛋白质的间隔之前，在SP-D生产的补偿性增加。因此，我们提议：1）表征纯化的嗜中性粒细胞衍生的丝氨酸蛋白酶对SP-D结构和生物活性的影响; 2）检查 体外嗜中性粒细胞介导的蛋白水解的机制，重点是“量子蛋白水解”和膜相关丝氨酸蛋白酶的潜在作用;和3）检查体内嗜中性粒细胞蛋白酶对SP-D降解和清除的潜在作用。丝氨酸蛋白酶的贡献将在体外使用蛋白酶缺乏的鼠中性粒细胞进行评估，这些酶在SP-D清除和降解中的潜在作用将在体内使用蛋白酶缺乏的鼠模型结合急性肺损伤模型进行检查。总之，这些研究应该提供重要的新信息，有关的机制，可以确定的数量和功能活性的SP-D在设置急性肺损伤。

Surfactant Protein D (SP-D) plays important roles in the defense against inhaled microorganisms, contributes to the pulmonary response to antigenic challenge, and participates in the regulation of surfactant lipid homeostasis. SP-D can directly interact with neutrophils, and can modulate the anti-viral, anti-bacterial, and anti-fungal functions of neutrophils in vitro. However, there is also evidence that neutrophils contribute to the degradation and clearance of SP-D in the setting of acute lung injury, suggesting a complex interplay between neutrophils and SP-D in vivo. We have recently observed that SP-D is specifically degraded by the three major human neutrophil serine proteases: neutrophil elastase (NE), cathepsin G (CG), and proteinase 3 (PR3) with the liberation of similar, high molecular weight, disulfide-crosslinked fragments; similar cleavage is mediated by murine neutrophils and whole neutrophil lysates. Given the above, we hypothesize the neutrophil-derived proteases specifically degrade SP-D within the functionally important lectin domains. We further hypothesize the neutrophil serine proteases contribute to the enhanced clearance of SP-D in the setting of LPS challenge, thereby contributing to a depletion of functional forms of this host defense protein in the interval prior to compensatory increases in SP-D production. Accordingly, we propose: 1) to characterize the effects of purified neutrophil-derived serine proteases on SP-D structure and biological activity; 2) to examine mechanisms of neutrophil-mediated proteolysis in vitro with emphasis on the potential roles of "quantal proteolysis" and membrane-associated serine proteases; and 3) to examine the potential roles of neutrophil proteases on SP-D degradation and clearance in vivo. The contributions of serine proteases will be assessed in vitro using protease-deficient murine neutrophils, and the potential roles of these enzymes in SP-D clearance and degradation will be examined in vivo using murine models of protease deficiency in combination with models of acute lung injury. Together, these studies should provide important new information relating to the mechanisms that could determine the amount and functional activity of SP-D in the setting acute lung injury.