Th17/IL-17 Might Play a Protective Role in CLL Immunity

Immune system disorders play an important role in the development and progression of CLL. Many deficiencies, contributing to disease progression, were found in T cell populations. Th17 cells represent a recently-discovered distinct lineage of helper T-cells, characterized by IL-17 secretion. IL-17 play an active role in inflammation and autoimmune diseases, however the role of IL-17 and Th17 cells in CLL immunopathogenesis remains undefined. We investigated IL-17A mRNA and IL-17A protein expression in peripheral blood (PB) CD4+ T cells and the plasma levels of IL-17 in 70 untreated patients with CLL in the context of clinical and immunological parameters. Th17 cell percentage was measured also in the bone marrow of CLL patients. The control group consisted of 20 healthy age-matched subjects.

Quantitative ‘real-time’ reverse transcription-polymerase chain reaction (qRT-PCR) was used for the analysis of IL-17A mRNA in PB CD4+ T-cells. Intracellular IL-17A expression in CD3+/CD4+cells was analyzed using a three-color flow cytometry technique. Plasma levels of IL-17A, IL-4 and IL-10 were measured by ELISA.

None of the CD4+ T cells in the samples obtained from healthy volunteers (HV) contained detectable amounts of IL-17 mRNA, whereas it could be found in 5 out of 70 CLL samples. All CLL patients with detectable IL-17 mRNA in T-cells were in 0 Rai stage and negative both for ZAP-70 and CD38 expression. It is possible that IL-17 mRNA in these cells is expressed only for a short time thus evading detection by PCR, or that CLL cells contain low amounts of the IL-17 transcript and the RT-PCR method was not sufficiently sensitive to detect these small amounts. Frequently, in HV as well as in CLL patients, the percentage of CD4+ T cells with intracellular IL-17 expression in non-activation assays was lower than 1%, comparable to the level of autofluorescence. Despite the fact that IL-17 mRNA was not detected in the T cells of the majority of CLL patients, IL-17 protein was present in T cells after PMA and ionomycin stimulation. We found a significantly higher median percentage of CD4+/CD3+/IL-17+ cells in CLL patients (18.2%) than in HV (2.9%) (p<0.01). Median percentage of Th17 cells was significantly higher in CLL patients in stages 0–1 according to Rai, as compared with stages 2–4 (36.2% vs 4.5%, p<0.05). There were no differences in Th17 percentages between the PB and BM of CLL patients. Accordingly, the IL-17 plasma level was significantly higher in CLL patients than in HV (101.9 pg/ml vs 75.6 pg/ml; p<0.05) and there was a significant correlation between Th17 cell percentage and IL-17 plasma level. There was also significant correlation between the percentages of Th17 and iNKT cells (R=0.56; p<0.05), and inverse correlations between the percentage of Th17 and: Treg cells (R=−0.28; p<0.05), CD4+IL-4+ (R=−0.55; p<0.05) and CD4+TNF+ T cells (R=−0.59; p<0.01). The percentage of Th17 inversely correlated with β2-microglobulin serum level (R=−0.29; p<0.05) and the expression of ZAP-70 (R=−0.244; p<0.05) and CD38 (R=−0.33; p<0.01). The plasma level of IL-17 inversely correlated with the stage of disease (R=−0.23; p<0.05), IL-10 (R=−0.56; p<0.01) and TNF (R=−0.66; p<0.01) plasma levels, CD38 antigen (R=−0.25; p<0.05) and ZAP-70 expression (R=−0.28; p<0.05). In patients requiring therapy during the observation period, the median percentage of Th17 cells and median plasma IL-17 level were significantly lower comparing to untreated ones (5.7% vs 23.1%, p<0.05; 53.8 vs 95.6 pg/ml, p<0.05; respectively). Moreover, median plasma IL-17A level correlated with the time from CLL diagnosis to the start of therapy (R=0.49; p<0.01). Conclusions: both the Th17 cell percentage, and the IL-17 plasma level are significantly higher in the PB of untreated CLL patients compared with the HV, and IL-17 mRNA expression was found only in the T cell of CLL patients, but not in the control group. Correlations found with disease activity parameters, the subsets of T cells involved in tumor surveillance, and also with the length of time from diagnosis to the start of therapy, suggest an important protective role for Th17 cells in CLL immunity.

No relevant conflicts of interest to declare.