Figure 6. Patient Immunoglobulin (Ig) Recognized β3 Domain of Low-Density Lipoprotein Receptor-Related Protein 4 (LRP4) and LG1 or LG2 Domain of Agrin.

(A) Schematic diagrams of LRP4 extracellular domain (ECD) and individual domains. (B, C) Identification of β3 domain as the epitope by ELISA (B) and by coprecipitation (C). (B) Healthy or patient Ig was immobilized on wells and incubated with alkaline phosphatase (AP)–tagged LRP4 proteins, and AP activity was assayed by ELISA. n = 3, **p < 0.01. (C) Lysates of HEK293 cells expressing respective LRP4 proteins were incubated with indicated Ig or anti-Flag antibody and bound proteins were detected by Western blotting. (D) Schematic diagrams of agrin constructs. (E) Agrin-LG123 and LG23, not agrin-LG3, bound patient Ig. n = 3.