Cellular expression and serum circulating levels of CD23 in B-cell chronic lymphocytic leukemia. Implications for prognosis

Background. CD23 is a functionally relevant molecule in B-cell chronic lymphocytic leukemia (CLL) which mediates growth and differentiation signals in B-cells. An intriguing feature of CD23 is its ability to be cleaved from the cell surface and released into the serum. Materials and Methods. Serum levels of soluble CD23 (sCD23) were determined with a sandwich enzyme immunoassay at the time of diagnosis in 90 previously untreated CLL patients, in order to evaluate whether they reflected disease activity and tumor load. Results were correlated with those dealing with CD23 expression on leukemic cells to verify whether the cellular counterpart determines serum levels. Results. CD23 was detected on peripheral blood mononuclear cells (PBMC) from 78 out of 90 (86.6%) B-CLL patients, without correlation with clinical stage. Circulating levels of sCD23 in the serum of patients with CLL were highly elevated in comparison to 15 normal controls (p < 0.0005); this increase reflected tumor mass as defined by either clinical stage (p < 0.0005) or bone marrow (BM) histology (p < 0.0005). Neither percentage nor absolute number of CD23(+) cells correlated with circulating levels. Interestingly, life expectancy was significantly shorter in patients with higher serum levels of sCD23 (p < 0.0005). When integrated into the Binet clinical staging system, sCD23 led to isolation of two subgroups with different prognosis among intermediate-risk patients. Furthermore, longitudinal studies support the idea that sCD23 can be utilized as an indicator of disease progression. Conclusions. sCD23 is a highly sensitive and suitable marker with prognostic potential in B-CLL.