IL-4 enhances expression of sIgM, but not sIgD, on CLL cells. Histogram of (A) sIgM and (D) sIgD expression on a representative CLL sample. Graph shows sIg expression at the start of the experiment (black dotted line) and at 24 hours in the presence (solid black line) or absence (dashed line) of IL-4 (10 ng/mL), respectively. Gray histogram, isotype control antibody. (B,E) Results (MFI minus isotype control) for cells treated with IL-4 or left untreated as a control (NA) for up to 72 hours. (C,F) All results expressed as MFI ratios from samples analyzed at 24 hours (C, n = 33; F, n = 29). (G-I) Correlation between the increase in sIgM [(sIgM MFI with IL-4) − (sIgM MFI without IL-4)] and prognostic markers. Samples are categorized according to (G) IGHV mutational status, (H) ZAP70 expression, and (I) CD38 expression. Error bars represent the standard error of the mean (SEM). Statistical significance was determined by either a paired (B,C,E,F) or unpaired (G-I) Student t test or Wilcoxon matched pairs signed rank test.