(A) Quantification of TH⁺ DNs in the SNpc at day 7 after MPTP (4 × 18 mg/kg) or saline treatment in WT and Rag1^–/– mice reconstituted with spleen cells from either C57BL/6 inbred or Ifng^–/– donors. All groups of animals are equally sensitive to MPTP-induced DN injury. *P < 0.05 compared with their saline counterparts; ^†P < 0.05 compared with their saline counterparts but not different from MPTP-treated WT mice (Tukey post-hoc analysis). (B) Quantification of TH⁺ DNs in the SNpc at day 7 after MPTP (4 × 18 mg/kg) or saline treatment in nonreconstituted Rag1^–/– mice (non rec. Rag1^–/–) and in Rag1^–/– mice reconstituted with spleen cells from either C57BL/6 or gld donors (WT rec. Rag1^–/– and gld rec. Rag1^–/–, respectively). Nonreconstituted Rag1^–/– mice and gld rec. Rag1^–/– mice are partially protected against MPTP-induced DN loss as compared with WT rec. Rag1^–/– animals. **P < 0.01 compared with MPTP-intoxicated WT rec. Rag1^–/– mice (Tukey post-hoc analysis). (A and B) Open symbols indicate saline-treated animals and filled symbols indicate MPTP-treated animals. Each symbol represents 1 individual animal. Bars represent the mean number of total nigral TH⁺ DNs. (C) Representative photomicrographs of mesencephalic sections immunostained for TH with Nissl counterstain from saline- or MPTP-treated WT rec. Rag1^–/– and gld rec. Rag1^–/– mice. Scale bar: 300 μm.