RESULTS Expression of the p 55 and p 75 TNF receptors on CD 19 + cells from CLL patients

We studied the expression of the two tumor necrosis factor (TNF) receptors, p55 and p75, on B cells from patients with chronic lymphocytic leukemia (CLL), and the presence of soluble TNF receptors in serum. Expression of membraneassociated receptors was quantified by double labeling of peripheral blood mononuclear cells (PBMC) with monoclonal antibodies against CD19 and p55/p75 TNF receptors and flow cytometry. A high fraction of the CDl9+ cells expressed the p55 receptor (44% f 34% [SO]) and p75 receptor (6lY0 k 31%). In healthy controls, 0% to 1% of the CD19+ cells expressed the p55 receptor and 0% to 10% expressed the p75 receptor. Incubation of CD19+ cells with 10 ng/mL of TNF increased the incorporation of thymidine in 11 patients tested, and this was decreased to 65% (P < .05) by antibodies to the p55 receptor or the p75 receptor, and to 35% f 7% (P < .001) when both antibodies were combined. With an enzyme-linked immunoassay, we measured soluble TNF