Soluble CD23 measurement by CBA: a convenient and reliable quantification method in chronic lymphocytic leukemia

The soluble form of the transmembrane glycoprotein CD23 corresponding to the low-affinity receptor for the immunoglobulin E (sCD23) is found in the serum of patients with chronic lymphocytic leukemia (CLL). In this disease, an increase in sCD23 level is predictive of poor prognosis at diagnosis as well as during clinical outcome. Quantification of sCD23 is classically performed by enzyme-linked immunosorbent assay (ELISA), a method not routinely used in hematology laboratories. Our aim was to apply cytometric bead array (CBA) technology to measure sCD23 levels. We tested 420 serum samples, 360 from patients and 60 from healthy volunteers. We selected three pairs of monoclonal antibodies recognizing the CD23 molecule that were tested in various conditions of temperature, centrifugation, washing, or chemical supplementation. Satisfactory performances in terms of repeatability (CV: 5%) and reproducibility (CV: 6%) were obtained with the selected pair of antibodies, with a threshold of positivity at 6 ng/mL. CBA and ELISA techniques were correlated with a Spearman coefficient at 0.99. The reproducibility and reliability of the sCD23 CBA assay were confirmed, with a Spearman coefficient at 0.99 in a series of 23 CLL patients and 13 controls tested in two laboratories equipped with different cytometers and using different lots of CBA reagents. Data obtained with serum and plasma samples were correlated with a Spearman coefficient at 0.99. Our study validates a simple method that allows the clinicians to benefit from an indicator of prognosis at the diagnosis as well as a marker of the evolution of CLL disease.