WT or PARP-1−/− mice were subjected to OVA sensitization followed by a single or triple challenge (Multiple) or left unchallenged. WT mice were administered i.p. 5 mg/kg of olaparib or saline 30 min after each challenge or left untreated. All mice were sacrificed 48 h later. Spleens from the different experimental groups were used to generate single-cell suspensions. a Cells were stained with antibodies to CD3e (145-2c11-APC) and CD4 (GK1.5-PE). b A portion of the cells was also subjected to intracellular staining with antibodies to Foxp3 (FJK-16s- PE) in addition to antibodies to CD4 (GK1.5-FITC) and CD25 (PC61.5- APC). Stained cells were then analyzed by FACS. Asterisk difference from control WT mice, p < 0.01; hash difference from WT-OVA challenged mice, p < 0.01.