Reduction in IL-33 Plasma Levels Might Be Involved in T Cell Dysregulation in Chronic Lymphocytic Leukemia (2013)

It is now clear that chronic lymphocytic leukemia (CLL) is a proliferative disorder that requires the help of its microenvironment to be maintained and to progress. In CLL, neoplastic B cells inhibit normal T lymphocytes through the impairment of the formation of the immunologic synapse in a contact-dependent manner [1]. However, the importance of T cells remains one of the most controversial areas in CLL research [2]. The alteration of several cytokines may also contribute to this T cell dysregulation. In this context, some recently discovered cytokines may have particular relevance, such as interleukin (IL) 33 and IL-31. IL-33 is a cytokine that drives cytokine production in type 2 innate lymphoid cells, T helper (Th)2 lymphocytes, mast cells, basophils, eosinophils, invariant natural killer T cells and natural killer cells [3,4]. IL-31 coordinates the interaction of different immune cells, including T cells, mast cells and eosinophils, with epithelial cells [5].In our study, we analyzed the plasma levels of IL-33 and IL-31 in patients with B-CLL. In the same subjects we also evaluated the lymphocyte immunophenotypical pattern, and we performed IgVH gene analysis, CD38 positivity and ZAP-70 expression to evaluate a possible correlation between IL concentrations and biological risk.The study population included 77 patients with B-CLL (38 female, 39 male) with a median age of 72.38 ± 11.1 years. All procedures followed were in accordance with the ethical standards of the responsible committee on human experimentation (institutional and national) and with the Helsinki Declaration of 1975, as revised in 2008. Informed consent for being included in the study was obtained from all patients.Plasma from 63 sex- and age-matched normal subjects were also included. In a small group of 7 patients the dosage of the cytokines was performed before and after different treatment protocols.IL-31 and IL-33 protein levels were measured using the DuoSet ELISA Development System kits (R&D Systems, Minneapolis, Minn., USA). Data were presented as interquartile range and range, except for age, which was presented as mean ± standard deviation. Statistical significance was set at p < 0.05.There was a significant difference (p < 0.0001) between the levels of IL-33 in patients affected by CLL (411.5 and 617.2 pg/ml) and those measured in controls (1,375.3 and 2,035.4 pg/ml; fig. 1). There was not a significant difference between the levels of IL-31 in patients affected by CLL (1,783.5 and 10,692.8 pg/ml) and those measured in controls (3,278.4 and 10,067.1 pg/ml).There was a notable difference, although not statistically significant (p = 0.072), between the IL-33 levels in CLL patients before and after therapy (83.67 and 1,421 vs. 837.22 and 1,790.38 pg/ml). There was a positive correlation in CLL patients between IL-31 plasma levels and IL-33 (rho = 0.962, p < 0.0001), while we found a negative correlation in patients between IL-31 levels and IL-33 and CD20 expression (rho = -0.6, p = 0.014 and rho = -0.43, p = 0.031, respectively). There was a positive correlation in patients between levels of IL-33 and CD3 expression (rho = 0.81, p = 0.027). No statistically significant differences were found in B-CLL subjects among the levels of IL-33 or IL-31 in the different stages of disease and there was not a significant correlation between IL-33 or IL-31 plasma levels with IgVH gene status, CD38 or ZAP-70 expression, lymphocyte count, LDH or β2 microglobulin levels.In leukemia patients, T cell function has been suppressed with the disease progress. To a degree, patients with CLL are all immunodeficient. Cytokines play a critical role in the control of the immune responses. IL-31 and IL-33 have pleiotropic actions ranging from antiviral immunity to the regulation of Th2 immune responses.In previous works we found a significant decrease of IL-33 plasma levels in patients affected by multiple myeloma, witha negative correlation between levels of IL-33 and stage, and the existence of low levels of IL-33 in patients with polycythemia vera and essential thrombocythemia [6,7]. To the best of our knowledge, ours is the first study to demonstrate decreased concentrations of IL-33 in patients with CLL, and this reduction might participate in the determination of changes in the immune system found in these patients.IL-33 in fact appears to drive Th2 responses. Podhorecka et al. [8] evaluated the Th1/Th2 balance in CLL patients, and indicated the dominance of T type 1 cells and T cell-mediated immunity in CLL patients that is shifted towards T type 2 during disease progression. The reduction in plasma levels of IL-33 might therefore justify the reduction of the Th2 response observed in these patients. Moreover, in our study we found a positive correlation between levels of IL-33 and CD3 expression in patients, and it is well known that significantly lower expression of CD3γ, ε and ζ chain genes, as well as the FcεRIγ gene, is found in CLL samples [9].Finally, by our results it is possible to detect the existence of an inverse correlation between plasma concentrations of IL-33 and CD20 expression. The concentrations of IL-33 seem to be able to modify the expression of CD20. It remains to be established whether this is due to a direct action of the cytokine, or if the data are secondary to a different condition. Nevertheless, the evidence that the therapeutic treatment of CLL tends to restore normal plasma levels of the cytokine is highly interesting. This could suggest a primitive action of the disease on plasma concentrations of the cytokine. Our study might contribute to a better understanding of the cellular immune features in CLL patients.