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bioRxiv · 10.1101/2023.12.18.572142

CD5L associates with IgM via the J chain

Wang, Y.·Su, C.·Ji, C.·Xiao, J.
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Abstract

CD5 antigen-like (CD5L), also known as Sp or AIM (Apoptosis inhibitor of macrophage), emerges as an integral component of serum immunoglobulin M (IgM). However, the molecular mechanism underlying the interaction between IgM and CD5L has remained elusive. In this study, we present a cryo-electron microscopy structure of the IgM pentamer core in complex with CD5L. Our findings reveal that CD5L binds to the joining chain (J chain) in a Ca2+-dependent manner and further links to IgM via a disulfide bond. We further show that CD5L reduces IgM binding to the mucosal transport receptor pIgR, but does not impact the binding of the IgM-specific receptor FcR. Additionally, CD5L does not affect IgM-mediated complement activation. These results offer new insights into our understanding of IgM and shed light on the functions of the IgM-CD5L complex in the immune system.

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Wang, Y., Su, C., Ji, C., Xiao, J.. 2023-12-18. CD5L associates with IgM via the J chain. https://doi.org/10.1101/2023.12.18.572142

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