Enhanced proliferation and defective activation-induced cell death of CD4+ T cells in childhood asthma.

Background: Hyperactivation of CD4+ T cells in peripheral blood and airway tissues has been suggested to play a key role in the development and maintenance of chronic inflammation in childhood asthma. However, the underlying mechanisms are not yet clear. Objective: To investigate alterations in serum levels of T helper cell-related cytokines, mitogen-stimulated CD4+ T cell proliferation and activation-induced cell death (AICD) in childhood asthma. Methods: 21 children with untreated asthma and 21 healthy volunteers (age and gender matched) participated in this study. Th1/Th2/Th17 cytokines in serum were analyzed by flow cytometry. CD4+ T cells were isolated from participants by using immuno-magnetic beads and were stimulated by phytohemagglutinin (PHA). Cell proliferation was evaluated with a Cell Counting Kit-8 (CCK-8). Activation induced cell death (AICD) of CD4+ T cells was also induced by PHA and apoptosis was assayed by annexin V/PI staining. Quantitative RT-PCR was carried out to analyze Fas and FasL mRNA expression. FLIP L , caspase-8 and Bcl-2 were detected by western blot analysis. Results: In children with asthma, the proliferative capacity of CD4+ T cells was enhanced and AICD was inhibited significantly, while serum IL-4, IL-10 and TNF were markedly higher compared with the control group. Fas mRNA expression in the asthma group was obviously lower than that in the control group, while no change was detected in FasL mRNA expression. Western blot analysis showed that the levels of the anti-apoptotic proteins, FLIP L and Bcl-2 in CD4+ T cells of the asthma group were significantly higher than in the control group. Spearman’s correlation tests showed that only IL-4 correlated positively with FLIP L and Bcl-2 expression, while IL-10 and TNF were unrelated to FLIP L and Bcl-2 expression. Conclusions: These results indicate that enhanced proliferation and defective AICD of CD4+ T cells influence the T cell-mediated inflammatory reaction in childhood asthma and that increased IL-4, FLIP L and Bcl-2 expression and decreased Fas expression jointly participate in these changes in cell proliferation and apoptosis. ression and decreased Fas expression jointly participate in these changes in cell proliferation and apoptosis.