Cytokine gene expression in B-cell chronic lymphocytic leukemia: evidence of constitutive interleukin-8 (IL-8) mRNA expression and secretion of biologically active IL-8 protein

Abstract

To extent our knowledge on the cytokines possibly involved in the pathophysiology of B-cell chronic lymphocytic leukemia (B-CLL), the mRNA expression of a panel of 10 cytokines was investigated on purified B-CLL cells using a reverse-transcriptase polymerase chain reaction method. Whereas negative RT-PCR signals were recorded for interleukin-1 alpha (IL-1 alpha), IL-2, IL-3, IL-4, IL-5, IL-7, tumor necrosis factor beta (TNF beta), and granulocyte-macrophage colony-stimulating factor, we detected the expression of IL-1 beta, IL-6 and TNF alpha. Furthermore, the constitutive expression of IL-8 mRNA was observed in all 17 B-CLL samples analyzed. mRNA expression was associated with the capacity of the leukemic cells to release IL-8 both constitutively (4.6 +/- 8.1 SD ng/mL) and, to a further extent, after stimulation (14.5 +/- 19.4 ng/mL). The circulating levels of IL-8 were also evaluated in 12 untreated B-CLL sera samples and the overall mean level was significantly higher (P < .01) than in normal sera. In addition, supernatants of purified B-CLL cells cultured in the presence of 12-O-tetradecanoylphorbol-13-acetate showed chemotactic activity towards neutrophils; this activity was neutralized in the presence of an anti-IL-8 antiserum. The mRNA for IL-8 was absent in five B-cell preparations from hairy cell leukemia cases and in four B-cell lines. Normal tonsil CD5+ B cells showed a low expression of IL-8 mRNA only in two of the nine preparations tested and the overall quantity of IL-8 released by these cells after 3 days' incubation was significantly lower compared with that released by B-CLL cells (0.4 +/- 0.3 and 1.6 +/- 0.9 ng/mL under basal and stimulated conditions, respectively). These findings point to an involvement of a member of the proinflammatory chemokine supergene family in human CD5+ B lymphocytes. The different IL-8 behavior observed between B-CLL cells and their normal counterpart is likely to reflect an activation state of the leukemic population.