Most antibodies produced in the body are of the IgA class. The dominant cell population producing them are plasma cells within the lamina propria of the gastrointestinal tract, but many IgA-producing cells are also found in the airways, within mammary tissues, the urogenital tract and inside the bone marrow. Most IgA antibodies are transported into the lumen by epithelial cells as part of the mucosal secretions, but they are also present in serum and other body fluids. A large part of the commensal microbiota in the gut is covered with IgA antibodies, and it has been demonstrated that this plays a role in maintaining a healthy balance between the host and the bacteria. However, IgA antibodies also play important roles in neutralizing pathogens in the gastrointestinal tract and the upper airways. The distinction between the two roles of IgA - protective and balance-maintaining - not only has implications on function but also on how the production is regulated. Here, we discuss these issues with a special focus on gut and airways.

中文翻译：

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了解你的敌人还是找到你的朋友？——粘膜表面 IgA 的诱导

体内产生的大多数抗体属于 IgA 类。产生它们的主要细胞群是胃肠道固有层内的浆细胞，但在气道、乳腺组织、泌尿生殖道和骨髓内也发现了许多产生 IgA 的细胞。大多数 IgA 抗体作为黏膜分泌物的一部分由上皮细胞转运到腔内，但它们也存在于血清和其他体液中。肠道中的大部分共生微生物群都被 IgA 抗体所覆盖，并且已经证明这在维持宿主和细菌之间的健康平衡方面发挥了作用。然而，IgA 抗体在中和胃肠道和上呼吸道的病原体方面也发挥着重要作用。IgA 的两种作用——保护性和维持平衡——之间的区别不仅对功能有影响，而且对生产的调节方式也有影响。在这里，我们讨论这些问题，特别关注肠道和气道。