作为空气交换的场所，肺组织永远暴露于大量的外来病原体。因此，肺已经形成了完善而复杂的免疫系统。除了物理和化学屏障作用之外，肺上皮细胞还可以通过表达 Toll 样受体 (TLR) 和其他模式识别受体以及分泌细胞因子来促进免疫防御。新的证据表明，肺上皮细胞可以产生和分泌免疫球蛋白（Igs），包括 IgM、IgA 或 IgG，从而发挥抗体功能。此外，已发现恶性转化的肺上皮细胞产生高水平的Ig，主要是IgG，其不履行抗体的作用，而是发挥促肿瘤活性。结构分析表明，由于独特的糖基化修饰，肺癌细胞产生的IgG的生物活性与正常肺上皮细胞产生的Igs不同。具体而言，唾液酸化 IgG (SIA-IgG) 在肿瘤干细胞中高表达，其特征是 Igγ CH1 的 Asn162 位点发生非传统的 N-糖基化修饰。已证明SIA-IgG依赖于这种独特的唾液酸化修饰来促进肿瘤发生、转移和免疫逃避。目前的研究结果证明，肺上皮细胞产生的Ig具有多方面的生物活性，包括生理条件下的免疫防御功能，同时在恶性转化过程中获得促肿瘤活性。这些见解具有作为新型生物标志物和靶标诊断和治疗肺癌的潜力。© 2024。Springer Nature Singapore Pte Ltd.

As the locus for air exchange, lung tissue is perpetually exposed to a significant quantity of foreign pathogens. Consequently, lung has developed a refined and intricate immune system. Beyond their physical and chemical barrier roles, lung epithelial cells can contribute to immune defence through the expression of Toll-like receptors (TLRs) and other pattern recognition receptors, along with the secretion of cytokines. Emerging evidence demonstrates that lung epithelial cells can generate and secrete immunoglobulins (Igs), including IgM, IgA, or IgG, thus performing antibody function. Moreover, malignantly transformed lung epithelial cells have been discovered to produce high levels of Ig, predominantly IgG, which do not fulfill the role of antibodies, but instead carries out tumour-promoting activity. Structural analysis has indicated that the biological activity of IgG produced by lung cancer cells differs from that of Igs produced by normal lung epithelial cells due to the unique glycosylation modification. Specifically, the sialylated IgG (SIA-IgG), characterised by a non-traditional N-glycosylation modification at the Asn162 site of Igγ CH1, is highly expressed in tumour stem cells. It has been demonstrated that SIA-IgG relies on this unique sialylation modification to promote tumorigenesis, metastasis, and immune evasion. Current results have proven that the Ig produced by lung epithelial cells has multifaceted biological activities, including immune defence functions under physiological conditions, while acquiring tumour-promoting activity during malignant transformation. These insights possess potential for the diagnosis and treatment of lung cancer as novel biomarkers and targets.© 2024. Springer Nature Singapore Pte Ltd.