Level of IL-17 in Thai SLE patients

Abstract

Systemic Lupus Erythematosus (SLE) is an autoimmune disorder which affects various systems. Currently, the etiology of this disease has not been fully elucidated. One of potential causes which may play an important role is the defects in cytokine network and the functions of T lymphocytes. Previously, it was reported that SLE patients showed elevated elevated level of various cytokines such as IL-1β IL-6 IL-23. The aim of this study was to investigate the level of cytokine IL-17 which could be produced by various cell types including T lymphocytes CD4+ T lymphocytes mainly producing IL-17 form a distinct lineage called Th17. Differentiation of Th17 is under the influence IL-1β/IL-6 and IL-23. Furthermore, IL-23 also plays an important role in maintaining the phenotype of Th17. In this study, 29 SLE patients at King Chulalongkorn Memorial Hospital were recruited and were divided based on SLEDAI score which is an indicator of the severity of disease. There were 13 patients in active stages and 16 patients in inactive stages and 10 normal subjects were used as control group. First, the frequency of T lymphocytes expressing IL-23R in PBMC was analyzed. The frequency of CD4+IL-23R+ and CD8+IL-23R+T lymphocytes in PBMC from SLE patients were found to be significantly higher than those of controls, both in freshly isolated PBMC (day 0) (p=0.0025, p=0.0201 and p=0.0021 for CD4+ and p=0.0021, p=0.0032 and p=0.0008 for CD8+ for the inactive, the active and the total SLE groups in comparison with normal subjects, respectively) and PBMC receiving ex vivo stimulation by anti-CD3 and CD28 antibodies (day 3) (p=0.0057, p=0.0011 and p=0.0007 for CD4+ and p=0.0041, p=0.0101 and p=0.0019 for CD8+ for the inactive, the active and the total SLE groups in comparison with normal subjects, respectively). When the frequency of T cells which could produce IL-17 was measured, PBMC from SLE patients showed significantly lower percentages of CD4+IL-17+ T lymphocytes than those from the control group in samples from day 0 (p=0.0219 and p = 0.0197 for the inactive and the total SLE in comparison with normal subjects, respectively) but the trend reversed on day 3 when SLE patients exhibited a tendency to have higher percentage of CD4+IL-17+ T cells. In contrast, the frequency of CD8+IL-17+T cells in SLE patients was significantly higher on day 3 (p=0.0007, p=0.0007, p=0.0120 and p=0.0007 for the inactive, the active and the total SLE in comparison with normal subjects, respectively), while there was no difference on day 0. When the level of IL-17 in serum and plasma were measured by ELISA, only two samples were found to show detectable IL-17 at 5.12-6.78 pg/ml, while the level in the rest of the samples was below detectable. When IL-23 was measured in sera by ELISA, all samples showed negative results. Therefore, the expression of IL-17A was analyzed by Realtime RT-PCR and it was found that PBMC from patients showed increased, but not statistically significant, level of IL-17A, when compared with the controls. Analysis of all results obtained in this study, the correlation was found to be significant between percentages of CD4+IL-23R+, CD8+IL-23R+T lymphocytes and CD4+IL-17+, CD8+IL-17+ T lymphocytes in SLE patients. Furthermore, the percentages of CD4+IL-23R+T cells at day 3 were found to have a correlation with IL-17A expression in SLE patients. When the active patients were compared against the inactive patients for all indicators investigated in this study, no statistically significant difference was detected. Taken together, these results suggest that T lymphocytes in SLE patients increase IL-23R and IL-17 expression, which may play an important role in pathology of SLE.