C-type lectins are carbohydrate-binding proteins that play important roles in the innate immune response to pathogen infections. Here, multi-step high performance liquid chromatography (HPLC), combined with mass spectrometry (MS), was used to isolate and identify proteins with antibacterial activity from the serum of Pinctada fucata martensii. Using this method, we obtained a novel isoform of C-type lectin (PmCTL-1). PmCTL-1 strongly inhibited gram-positive bacteria. The complete cDNA sequence of PmCTL-1 was 636 bp in length, and encoded a protein 149 amino acids long, containing a typical carbohydrate recognition domain (CRD). A phylogenetic analysis based on a multiple sequence alignment indicated that PmCTL-1 was highly similar to C-type lectins from other mollusks. Fluorescent quantitative real-time PCR analysis showed that PmCTL-1 mRNA was strongly upregulated in the mantle of healthy P.f. martensii, but was expressed only at low levels in the gill, gonad, hepatopancreas, adductor muscle, and hemocytes. PmCTL-1 expression levels in the mantle and hemocytes increased significantly in response to bacterial stimulation. This study provides a valuable framework for further explorations of innate immunity and the immune response in mollusks.

C型凝集素是碳水化合物结合蛋白，在对病原体感染的天然免疫反应中起重要作用。在这里，多步高效液相色谱法（HPLC）与质谱（MS）结合使用，从马氏梭菌（Pinctada fucata martensii）血清中分离和鉴定了具有抗菌活性的蛋白质。使用此方法，我们获得了C型凝集素（PmCTL-1）的新型同工型。PmCTL-1强烈抑制革兰氏阳性细菌。PmCTL-1的完整cDNA序列长度为636 bp，编码一个149个氨基酸的蛋白质，其中包含典型的碳水化合物识别结构域（CRD）。基于多序列比对的系统发育分析表明，PmCTL-1与其他软体动物的C型凝集素高度相似。荧光定量实时PCR分析显示，PmCTL- 1 mRNA在健康Pf martensii的外套中强烈上调，但仅在g，性腺，肝胰腺，内收肌和血细胞中低表达。响应细菌刺激，套层和血细胞中的PmCTL-1表达水平显着增加。该研究为进一步探索软体动物的先天免疫和免疫应答提供了有价值的框架。