Department of Medicine, Boston University School of Medicine, Boston, MA 02118, USA.
J Innate Immun. 2010;2(3):267-79. doi: 10.1159/000272313. Epub 2009 Dec 24.
Surfactant protein D (SP-D) plays important roles in innate defense against respiratory viruses [including influenza A viruses (IAVs)]. Truncated trimers composed of its neck and carbohydrate recognition domains (NCRDs) bind various ligands; however, they have minimal inhibitory activity for IAV. We have sought to find ways to increase the antiviral activity of collectin NCRDs. Cross-linking of the SP-D NCRD with nonblocking monoclonal antibodies (mAbs) markedly potentiates antiviral activity. In the present report, we demonstrate that F(ab')2 [but not F(ab')1] fragments of a cross-linking mAb have similar effects. Hence, cross-linking activity, but not the Fc domain of the mAb, is needed for increased antiviral activity. In contrast, the Fc domain of the mAb was important for increasing viral uptake or respiratory burst responses of human neutrophils. Our NCRD constructs contain an S protein binding site. Herein, we show that a multivalent S protein complex caused cross-linking and also increased the antiviral activity of NCRDs. NCRDs of conglutinin and CL43 had greater intrinsic antiviral activity than those of SP-D or mannose-binding lectin. Based on motifs found in these serum collectins, we have constructed mutant versions of the human SP-D NCRD that have increased antiviral activity. These mutant NCRDs also had potentiated activity after cross-linking with F(ab')2 fragments or S protein complexes. Hence, the antiviral activity of NCRDs can be increased by 2 distinct, complementary strategies, namely cross-linking of NCRDs through various means and mutagenesis of CRD residues to increase viral binding. These findings may be relevant for antiviral therapy.
表面活性蛋白 D（SP-D）在抵抗呼吸道病毒（包括甲型流感病毒（IAV））的先天防御中发挥重要作用。由其颈部和碳水化合物识别结构域（NCRD）组成的截短三聚体结合各种配体；然而，它们对 IAV 的抑制活性最小。我们一直在寻找方法来提高集胞素 NCRD 的抗病毒活性。SP-D NCRD 与非阻断性单克隆抗体（mAb）交联可显著增强抗病毒活性。在本报告中，我们证明交联 mAb 的 F(ab')2[但不是 F(ab')1]片段具有相似的作用。因此，增加抗病毒活性需要交联活性，而不需要 mAb 的 Fc 结构域。相反，mAb 的 Fc 结构域对于增加人嗜中性粒细胞的病毒摄取或呼吸爆发反应很重要。我们的 NCRD 构建体包含 S 蛋白结合位点。在此，我们表明多价 S 蛋白复合物引起交联，并且还增加了 NCRD 的抗病毒活性。结合素和 CL43 的 NCRD 比 SP-D 或甘露糖结合凝集素的 NCRD 具有更高的内在抗病毒活性。基于在这些血清凝集素中发现的基序，我们构建了具有增强抗病毒活性的人 SP-D NCRD 的突变体。这些突变 NCRD 在用 F(ab')2 片段或 S 蛋白复合物交联后也具有增强的活性。因此，NCRD 的抗病毒活性可以通过 2 种不同的、互补的策略来增加，即通过各种方法交联 NCRD 和突变 CRD 残基以增加病毒结合。这些发现可能与抗病毒治疗有关。
