Protein Expression Profiling of Cytokines and Cytokine Receptors on Purified Chronic Lymphocytic Leukemia Cells.

Chronic lymphocytic leukemia (CLL) B-cells rapidly undergo apoptosis when cultured in vitro, which contrasts with their prolonged survival in vivo. Multiple cytokines and cytokine receptors are believed to work together to regulate the survival of CLL cells. The literature is conflicting as to whether the CLL cells themselves produce significant amounts of cytokines compared with normal B-cells and how the CLL cells respond to these cytokines. This discrepancy is largely due to the different experimental conditions that have been used whereby various amounts of exogenous cytokines were introduced into the experimental system from, for example, the serum used to supplement the culture medium and the lysate or conditioned medium of CLL cells where other types of mononuclear cells were not removed. The aim of the current study is to reveal the intrinsic production and secretion of cytokines and cytokine receptors in CLL cells when exogenous sources are minimized. We purified CD19⁺ cells by magnetic beads from peripheral blood mononuclear cells of five CLL patients who had stage I or II disease and had not received any therapy. CD19⁺ cells from healthy donors were used as control. We used a cytokine antibody array approach that simultaneously measured 174 cytokines and cytokine receptors. We determined both intracellular levels in purified CLL cells and secreted levels in serum-free conditioned medium. The intracellular levels of cytokines and cytokine receptors of the purified CLL cells and the normal B-cells were not significantly different. However, the secretion of interleukin-6 (IL-6) was 3.0 times lower (p = 0.038) and that of eotaxin was 2.2 times higher (p = 0.028) in CLL-conditioned medium than in normal B-cell-conditioned medium. We further studied the effect of IL-6 and anti-IL-6 antibody on the apoptosis of purified CLL B-cells in serum-free culture, but no significant change was found in the presence or absence of IL-6 or IL-6 antibody. Except for IL-6 and eotaxin, our results suggest that CLL cells and their normal counterparts produce and secrete similar amounts of cytokines and cytokine receptors in vitro and that the in vivo longevity of CLL cells may be due to the concerted effects of various molecules and cellular interactions in the microenvironment.