Antibodies are key elements of protective immunity. In the mucosal immune system in particular, secretory immunoglobulin A (SIgA), the most abundantly produced antibody isotype, protects against infections, shields the mucosal surface from toxins and environmental factors, and regulates immune homeostasis and a peaceful coexistence with our microbiota. However, the dark side of IgA biology promotes the formation of immune complexes and provokes pathologies, e.g., IgA nephropathy (IgAN). The precise mechanisms of how IgA responses become deregulated and pathogenic in IgAN remain unresolved. Yet, as the field of microbiota research moved into the limelight, our basic understanding of IgA biology has been taking a leap forward. Here, we discuss the structure of IgA, the anatomical and cellular foundation of mucosal antibody responses, and current concepts of how we envision the interaction of SIgA and the microbiota. We center on key concepts in the field while taking account of both historic findings and exciting new observations to provide a comprehensive groundwork for the understanding of IgA biology from the perspective of a mucosal immunologist.

抗体是保护性免疫的关键要素。特别是在粘膜免疫系统中，分泌型免疫球蛋白 A (SIgA) 是产生最多的抗体同种型，可防止感染，保护粘膜表面免受毒素和环境因素的影响，并调节免疫稳态并与我们的微生物群和平共处。然而，IgA 生物学的阴暗面会促进免疫复合物的形成并引发病理，例如 IgA 肾病 (IgAN)。IgA 反应如何在 IgAN 中变得失调和致病的确切机制仍未得到解决。然而，随着微生物群研究领域成为众人瞩目的焦点，我们对 IgA 生物学的基本理解已经有了飞跃。在这里，我们讨论 IgA 的结构，粘膜抗体反应的解剖学和细胞基础，以及我们如何设想 SIgA 和微生物群相互作用的当前概念。我们以该领域的关键概念为中心，同时考虑历史发现和令人兴奋的新观察结果，为从黏膜免疫学家的角度理解 IgA 生物学提供全面的基础。