Reactivity and specificity of expressed P-7–specific BCRs. For this ELISA recombinant P-7 was used as a coat. The BCR of a patient with a P-7–specific IgM paraprotein that was cloned from the patient's lymph node involved by WM (black circles) had the same anti–P-7 specificity as the patient's serum containing the IgM paraprotein (black squares). There was no reactivity in the serum of a patient with an IgM-MGUS with a non–P-7-specific paraprotein (gray rhombus). The BCR of a patient with chronic lymphocytic leukemia with specificity for the FAM32A protein showed no reactivity (control; black triangle). The starting dilution of the sera was 10⁸ and the starting concentration of the expressed BCRs was 10 μg/mL.