CTLA4 and infection: In particular, the drastic reductions in suppressive potency that occurs for Tregs isolated from mice day 5 compared with day 37 after infection is associated with significant reductions in CTLA-4 expression and increased expression of GITR on both bulk Foxp3+ Tregs and Salmonella FliC431–439-specific Foxp3+ Tregs (Figure 7).