Pneumocyte-Derived Host Defence Lectins

表面活性剂蛋白D （SP-D）在抵御吸入微生物、参与肺对抗原攻击的反应、参与表面活性剂脂质稳态的调节等方面发挥重要作用。SP-D可直接与中性粒细胞相互作用，在体外可调节中性粒细胞的抗病毒、抗菌、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 (PR3)，释放出类似的、高分子量的、二硫交联的片段；类似的分裂是由小鼠中性粒细胞和整个中性粒细胞裂解物介导的。鉴于上述，我们假设

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.