Fig. 4: CD5L diminishes IgM binding to pIgR but not to FcμR.

a and b SPR analyses of the interactions between immobilized FcμR-D1 and Fcμ–J or Fcμ–J–CD5L. Twofold serial dilutions of Fcμ–J–CD5L or Fcμ–J (both from 40 to 2.5 nM) were passed through immobilized FcμR-D1 on the CM5 chip. c Structural insights indicate that CD5L is unlikely to disrupt the IgM–FcμR interaction. Teal, light coral, and gold represent Fcμ chains, J chain, and CD5L of the Fcμ–J–CD5L complex, while the grey and purple illustrate Fcμ–J and FcμR-D1 from the human Fcμ–J–FcμR-D1 complex (PDB ID: 7YTD), respectively. d and e SPR analyses of the interactions between immobilized pIgR-SC and Fcμ–J or Fcμ–J–CD5L. Twofold serial dilutions of Fcμ–J–CD5L (from 80 to 5 nM) or Fcμ–J (from 320 to 20 nM) were passed through biotinylated pIgR-SC immobilized on a SA chip. f Structural analyses suggest that CD5L hinders the IgM–pIgR interaction. Fcμ–J and pIgR of the human Fcμ–J–pIgR complex (PDB ID: 6KXS) are shown in grey and blue, respectively.