Levels and relative molecular mass estimation of the serum FcμR. (A) Serum levels in arbitrary units of FcμR in healthy donors (n = 31) and MT-CLL (n = 22), UM-CLL (n = 25), and untyped CLL patients (n = 55) were determined by a sandwich ELISA as described in “ELISA for soluble FcμR.” The horizontal line indicates arithmetic mean. UD indicates undetectable. (B) Correlation of soluble FcμR levels with blood lymphocyte (Lym) counts. The values of solFcμR level (units) and blood lymphocyte count (× 10³/μL) in each patient or donor are plotted along the y-axis and x-axis, respectively. ●, ▴, and ■ indicate mutated (MT), unmutated (UM), and untyped (ND) CLL patients, respectively, whose lymphocytes constitute ≥ 50% of WBCs; and ™, Δ, and £ indicate MT, UM, and ND CLL patients, respectively, whose lymphocytes constitute < 50% of WBCs. (C) Western blot analysis of membrane-bound and serum FcμR. (Left) Plasma membrane proteins on CLL cells were labeled with biotin, incubated with isotype-matched control (cont.) or anti-FcμR mAb, immunoprecipitated, and immunoblotted as described in “Western blot analysis of membrane-bound and soluble FcμR.” (Right) Serum FcμR proteins from a healthy donor and 2 different CLL patients were immunoprecipitated and analyzed by protein blot using a mixture of biotin-labeled anti-FcμR mAbs (HM14 and HM7) plus HRP-SA, before visualization by ECL. Size markers (kilodaltons) are indicated. Essentially the same results were obtained with sera from 8 other CLL patients (data not shown).