Absence of donor CB2R expression exacerbates the severity of acute GVHD. (A) Percentage of CD4⁺ and CD8⁺ T cells in the spleen of wild-type (WT; n = 5) and CB2R^−/− (n = 6) mice. (B-C) Percentage of CD4⁺ Foxp3⁺, naïve (CD62L^hi CD44^lo), central memory (CD62L^hi CD44^hi), and effector memory (CD62L^lo CD44^hi) CD4⁺ T cells (B) and naïve, central memory, and effector memory CD8⁺ T cells (C) in the spleen of WT B6 and CB2R^−/− mice. Data are cumulative results from 5 to 6 mice per group and are presented as the mean ± standard deviation. (D) Representative dot plots of CD4⁺ and CD8⁺ T-cell populations are shown together with the gating approach that was used for the data in panels B and C. (E) Lethally irradiated (900 cGy) Balb/c recipients received transplants of bone marrow (BM) alone from B6 mice (5 × 10⁶; n = 9) or BM and spleen cells (adjusted to yield an αβ T-cell dose of 0.6 × 10⁶ cells) from B6 (n = 15) or CB2R^−/− (n = 15) animals. Overall survival is depicted. Results are from 3 experiments. (F) Lethally irradiated (1100 cGy) FVB mice received transplants of B6 BM alone (n = 9), B6 BM and spleen cells (n = 17), or CB2R^−/− BM and spleen cells (n = 19; adjusted to yield an αβ T-cell dose of 0.85 × 10⁶ cells). Overall survival is depicted. Results are from 3 experiments. (G-H) Lethally irradiated Balb/c mice were transplanted with BM and spleen cells (adjusted to yield an αβ⁺ T-cell dose of 0.6 × 10⁶ to 0.8 × 10⁶) from B6 or CB2R^−/− animals. Animals receiving transplants of B6 BM alone served as controls. The absolute numbers of CD4⁺ and CD8⁺ T cells in the colon, liver, and lung 14 days posttransplantation are depicted in panel G (n = 12-20 per group), and absolute numbers of CD4⁺ or CD8⁺ interferon-γ–positive (IFN-γ⁺) T cells in the same organs are shown in panel H (n = 9-15 per group). Data are presented as the mean ± SD. Results are from 3 to 4 experiments. (I) Irradiated Balb/c recipients received transplants of B6 BM and spleen cells (adjusted to yield an αβ T-cell dose of 0.8 × 10⁶ cells). Animals were treated with the CB2R antagonist SR144528 (3 mg/kg; n = 10) or an equivalent amount of vehicle (n = 10) for 14 days beginning on the day of transplantation. Balb/c mice receiving transplants of B6 BM alone and then treatment with either vehicle (n = 6) or SR144528 (n = 3) served as controls. Results are from 2 experiments. (J) Lethally irradiated (1100 cGy) B6 (n = 15) or CB2R^−/− (n = 15) animals received transplants of Balb/c BM and spleen cells (adjusted to yield an αβ T-cell dose of 5 × 10⁶ to 5.5 × 10⁶ cells). Balb/c mice receiving transplants of B6 BM alone (n = 9) served as controls. Results are from 3 experiments. *P < .05, **P < .01, ****P < .0001. TCR, T-cell receptor.