Effect of All-Trans Retinoic Acid (ATRA) on Viability, Proliferation, Activation and Lineage-Specific Transcription Factors of CD4+ T Cells

All-trans retinoic acid (ATRA), as an active metabolite of vitamin A, has been shown to affect immune cells. This study was performed to evaluate the effect of ATRA on viability, proliferation, activation and lineage-specific transcription factors of CD4+ T cells. CD4+ T cells were  separated  from  heparinized  blood  of  healthy  donors  and  were  cultured  in conditions, some with, some without ATRA. Viability was assessed by PI  flowcytometry and proliferation was measured by MTT assay. CD69 expression was determined by flowcytometry as a measure of cell activation. Lineage-specific transcription  factors  (FOXP3,  RORγt  and  T-bet)  were  examined  by intracellular staining and flowcytometry. High doses of ATRA (0.1-1 mM) caused extensive cell death in both PBMCs and CD4+ T cells. Doses of ATRA equal to or lower than 10 µM did not  adversely affect cell viability and proliferation in comparison to  culture medium without ATRA. Doses of ATRA between 10 µM and 1nM significantly increased cell activation when compared  to  culture medium without  ATRA. ATRA could increase FOXP3+  and also FOXP3+RORγt+ T cells while it decreased RORγt+ and T-bet+ T cells. This study showed that doses of ATRA up to 10 µM are safe when using with CD4+  T cells in terms of cell viability, proliferation and activation. We  could  also  show  that  ATRA  diverts  the  human  immune  response  in  neutral conditions (without adding polarizing cytokines) by increasing FOXP3+  cells and decreasing RORγt+  cells. ATRA could be regarded as a potential therapy in inflammatory conditions and autoimmunities.