Kievits F, Kijlstra A
Immunology. 1985 Mar;54(3):449-56.
In the study described here, the effect of human tears and purified lactoferrin was investigated on the deposition of complement components on solid-phase bound immune complexes. After incubating immune complexes with fresh normal human serum, the deposition of complement components (C3, C4 and C5) was measured with an ELISA technique. Rabbit antibodies were used as a constituent of the immune complexes, and so both alternative and classical complement pathway activation could be studied. The addition of human tears or purified lactoferrin to this system resulted in the inhibition of classical pathway deposition of C3 and C5, while C4 deposition was not affected. High concentrations of human tears also inhibited alternative pathway C3 deposition on immune complexes, whereas lactoferrin did not detectably affect this pathway. The inhibition of complement activation by tears was not due to a masking of the immune complexes or the already deposited C3. Experiments with purified lactoferrin furthermore showed that lactoferrin did not bind to the complexes, either before or during complement activation. These findings suggest that the complement inhibitory effect is probably taking place in the fluid phase. Saturation of lactoferrin with iron or copper ions resulted in a markedly diminished effect on the capacity of lactoferrin to inhibit complement activation. C4 deposition on immune complexes was not affected by lactoferrin, which suggested that the inhibition of the classical pathway was due to an effect on the classical C3 convertase. The fact that lactoferrin inhibits the classical, but not the alternative C3 convertase, suggests that the effect is probably not mediated through a competition for certain trace metal ions, but may be caused by protein-protein interactions. The findings reported here indicate that lactoferrin may play an important anti-inflammatory role by modulating activation of the complement system. This observation adds a new property to the already described functions of the iron-binding protein lactoferrin.
在本研究中，研究了人眼泪和纯化乳铁蛋白对补体成分在固相结合免疫复合物上沉积的影响。用新鲜正常人血清孵育免疫复合物后，采用酶联免疫吸附测定（ELISA）技术检测补体成分（C3、C4和C5）的沉积情况。兔抗体用作免疫复合物的组成成分，因此可以研究替代途径和经典补体途径的激活。向该系统中加入人眼泪或纯化乳铁蛋白可抑制C3和C5的经典途径沉积，而C4沉积不受影响。高浓度人眼泪也可抑制替代途径C3在免疫复合物上的沉积，而乳铁蛋白对该途径无明显影响。眼泪对补体激活的抑制作用并非由于免疫复合物或已沉积的C3被掩盖。此外，用纯化乳铁蛋白进行的实验表明，乳铁蛋白在补体激活之前或期间均不与复合物结合。这些发现表明，补体抑制作用可能发生在液相中。乳铁蛋白用铁或铜离子饱和后，对其抑制补体激活能力的影响明显减弱。乳铁蛋白对免疫复合物上C4沉积无影响，这表明经典途径的抑制是由于对经典C3转化酶的作用。乳铁蛋白抑制经典而非替代C3转化酶这一事实表明，其作用可能不是通过竞争某些痕量金属离子介导的，而可能是由蛋白质-蛋白质相互作用引起的。此处报道的研究结果表明，乳铁蛋白可能通过调节补体系统的激活发挥重要的抗炎作用。这一观察结果为铁结合蛋白乳铁蛋白已描述的功能增添了一项新特性。
