IgA antibodies are key immune effectors against invading pathogens but also possess essential immunoregulatory functions. Detecting and quantifying human IgA⁺ B-cell subsets and secreted IgA molecules is needed for investigating the protective, modulatory and pathophysiologic roles of IgAs. Here, we produced a recombinant tagged trimeric form of the streptococcal IgA-binding peptide (SAP) by transient transfection-based eukaryotic expression system. The trimeric SAP (tSAP) probe had a higher production yield and apparent binding affinity to human IgA1 and IgA2 immunoglobulins when compared to the dimeric SAP molecule classically used to purify IgAs. tSAP bound both monomeric and dimeric IgAs, and allowed immunoblot detection and ELISA quantification of serum IgA antibodies in humans and non-human primates. Fluorescently labeled tSAP also permitted an accurate quantification of circulating human blood IgA-expressing memory B cells by flow-cytometric analyses. Thus, the easy-to-produce high affinity recombinant tSAP probe we developed is a versatile and valuable tool to quantify secreted and membrane-bound human but also primate IgA immunoglobulins.

IgA抗体是针对入侵病原体的关键免疫效应物，但也具有基本的免疫调节功能。检测和定量人类IgA ⁺B细胞亚群和分泌的IgA分子是研究IgA的保护，调节和病理生理作用所必需的。在这里，我们通过基于瞬时转染的真核表达系统生产了链球菌IgA结合肽（SAP）的重组标记三聚体形式。与传统上用于纯化IgA的二聚SAP分子相比，三聚SAP（tSAP）探针具有更高的产量和对人IgA1和IgA2免疫球蛋白的表观结合亲和力。tSAP结合了单体IgA和二聚IgA，并允许对人类和非人类灵长类动物的血清IgA抗体进行免疫印迹检测和ELISA定量。荧光标记的tSAP还可以通过流式细胞术分析准确定量循环表达人血的IgA表达记忆B细胞。从而，