Detection of Foreign Antigen-specific CD4(+)Foxp3(+) Regulatory T Cells by MHC Class II Tetramer and Intracellular CD154 Staining.

The unrestricted population of CD4(+)Foxp3(+) regulatory T (Treg) cells, which have been known to control the expression of autoimmune diseases and protective immunity to inflammatory reactions, has led to greater appreciation of functional plasticity. Detecting and/or isolating Ag-specific CD4(+)Foxp3(+) Tregs at the single cell level are required to study their function and plasticity. In this study, we established and compared both MHC class II tetramer and intracellular CD154 staining, in order to detect CD4(+)Foxp3(+) Treg specific for foreign Ag in acute and chronic infections with lymphocytic choriomeningitis virus (LCMV). Our results revealed that MHC class II tetramer staining showed a lower detection rate of LCMV GP66-77-specific CD4(+) T cells because most of MHC class II tetramers were unbound and unstable when combined staining was performed with intracellular cytokines. In contrast, intracellular CD154 staining was revealed to be easier and simple for detecting LCMV GP66-77-specific CD4(+) T cells, compared to MHC class II tetramer staining. Subsequently, we employed intracellular CD154 staining to detect LCMV GP66-77-specific CD4(+)Foxp3(+) Tregs using Foxp3(GFP) knock-in mouse, and found that LCMV GP66-77-specific CD4(+)Foxp3(+) Tregs and polyclonal CD4(+)Foxp3(+) Tregs showed differential expansion in mice infected with LCMV Arms or Cl13 at acute (8 and 13 days pi) and chronic phases (35 days pi). Therefore, our results provide insight into the valuable use of intracellular CD154 staining to detect and characterize foreign Ag-specific CD4(+)Foxp3(+) Treg in various models.