Curcumin regulates the differentiation of naïve CD4+T cells and activates IL-10 immune modulation against acute lung injury in mice.

Objectives: Acute lung injury/acute respiratory distress syndrome (ALI/ARDS) is one type of respiratory failure characterized by rapid onset of widespread inflammation in the lungs. Curcumin has been reported to be an anti-inflammatory factor through enhancing the function of regulatory T cells (Tregs). This study aimed to explore the effect of curcumin on the differentiation of Tregs and the role of curcumin in ALI/ARDS.

Methods: A cecal ligation and puncture (CLP)-induced acute lung injury mouse model was used to explore the effect of curcumin in ALI/ARDS. The severity of lung injury was evaluated. Immunohistochemistry of IL-17A and MPO in lung tissue was examined. Treg-related cytokine levels in serum and bronchoalveolar lavage fluid (BALF) were tested. The expression of nuclear factor-kappa B (NF-κB) in lung tissue was detected. Macrophages in lung tissue were detected by immunofluorescence. Splenic CD4+CD25+FOXP3+ Tregs were quantified, and the differentiation of Tregs from naïve CD4 + T cell and STAT5 was evaluated. The expression of IL-10 during naïve CD4 + T cell differentiation in vitro was tested.

Results: Curcumin alleviated lung injury in the induced CLP mouse model and suppressed inflammation. IL-17A, MPO-producing neutrophils, and NF-κB p65 expression in lungs of CLP mice decreased significantly after pretreatment with curcumin. We found curcumin could regulate M1/M2 macrophage levels in lungs of CLP mice. This may have been through regulating the differentiation of Tregs and the production of Treg-derived IL-10. Treg-derived IL-10 is the main factor that could affect macrophage polarization. We found curcumin could increase Treg proportions in vivo and up-regulate IL-10 expression in serum and BALF of CLP mice. In our in vitro experiments, we found curcumin could promote Treg differentiation and increase the production of IL-10.

Conclusions: Curcumin can reduce the degree of severity of ALI and uncontrolled inflammation through promoting the differentiation of naïve CD4 + T cells to CD4+ CD25+ FOXP3+ Tregs. Curcumin promotes the conversion of macrophages from M1 to M2. The differentiation of Tregs induced by curcumin may be one source of IL-10 immune modulation.