Tetraspanin CD81在细胞间相互作用和细胞运输调控中发挥重要作用。这种胆固醇载体跨膜蛋白是多种病毒的共受体，包括HCV、HIV-1和基孔肯亚病毒，利用大的细胞外环EC2进入细胞。CD81也是抗癌靶点，与肿瘤细胞增殖和移动以及转移有关。CD81信号传导有助于固体肿瘤的发展（尤其是结肠癌、肝癌和胃癌）并与B细胞淋巴瘤的侵袭性有关。各种蛋白质伴侣可以与CD81互动，不仅可以调节病毒的附着和摄取（如HCV E2、claudin-1、IFIM1），还可以促进肿瘤的生长和传播（CD19、CD44、EWI-2）。CD81-蛋白质相互作用可以通过靶向CD81的细胞外域的分子进行调节，这些分子被研究为抗病毒和/或抗癌剂。已经开发了几种抗-CD81单克隆抗体，尤其是抗侵袭和转移三阴性乳腺癌细胞的mAb 5A6。CD81-EC2也可以通过天然产物（如东青霉素和树脂酸A-B）和合成化合物（如苯并噻唑喹啉衍生物）进行靶向。它们是较弱CD81结合剂，但为设计针对开放EC2环的新化合物提供模板。目前没有正在开发的抗CD81化合物，但这种结构上经过充分表征的四螺旋蛋白值得更深入地考虑作为药物靶点。

Tetraspanin CD81 plays major roles in cell-cell interactions and the regulation of cellular trafficking. This cholesterol-embarking transmembrane protein is a co-receptor for several viruses, including HCV, HIV-1 and Chikungunya virus, which exploits the large extracellular loop EC2 for cell entry. CD81 is also an anticancer target implicated in cancer cell proliferation and mobility, and in tumor metastasis. CD81 signaling contributes to the development of solid tumors (notably colorectal, liver and gastric cancers) and has been implicated in the aggressivity of B-cell lymphomas. A variety of protein partners can interact with CD81, either to regulate attachment and uptake of viruses (HCV E2, claudin-1, IFIM1) or to contribute to tumor growth and dissemination (CD19, CD44, EWI-2). CD81-protein interactions can be modulated with molecules targeting the extracellular domain of CD81, investigated as antiviral and/or anticancer agents. Several monoclonal antibodies anti-CD81 have been developed, notably mAb 5A6 active against invasion and metastasis of triple-negative breast cancer cells. CD81-EC2 can also be targeted with natural products (trachelogenin and harzianoic acids A-B) and synthetic compounds (such as benzothiazole-quinoline derivatives). They are weak CD81 binders but offer templates for the design of new compounds targeting the open EC2 loop. There is no anti-CD81 compound in clinical development at present, but this structurally well-characterized tetraspanin warrants more substantial considerations as a drug target.