Glycan-independent binding and internalization of human IgM to FCMR, its cognate cellular receptor

Katy A Lloyd1, Jiabin Wang2, Britta C Urban1

  • 1Liverpool School of Tropical Medicine, Pembroke Place, Liverpool, L3 5QA, UK.

Scientific Reports
|February 24, 2017
PubMed

IgM is the first antibody to be produced in immune responses and plays an important role in the neutralization of bacteria and viruses. Human IgM is heavily glycosylated, featuring five N-linked glycan sites on the micro chain and one on the J-chain. Glycosylation of IgG is known to modulate the effector functions of Fcγ receptors. In contrast, little is known about the effect of glycosylation on IgM binding to the human Fcmicro receptor (hFCMR). In this study, we identify the Cmicro4 domain of IgM as the target of hFCMR, and show that binding and internalization of IgM by hFCMR is glycan-independent. We generated a homology-based structure for hFCMR and used molecular dynamic simulations to show how this interaction with IgM may occur. Finally, we reveal an inhibitory function for IgM in the proliferation of T cells.

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