Butyrate restrains the IR-induced intratumoral innate and adaptive immune response. (A) C57BL/6 mice (n = 4/group) were injected s.c. with 10⁶ MC38-OVA cells. Established tumors were irradiated (20 Gy) on day 10 after tumor inoculation. Tumor-bearing mice were intratumorally injected with 2 μmol of NaBu on days 1, 4, and 7 after IR. Tumors were harvested on day 10 after IR and processed for analysis of IFNγ production using Kb-OVA (SIINFEKL) peptide as the model antigen in an ELISPOT assay. (B) C57BL/6 mice (n = 4/group) were injected s.c. with 10⁶ MC38-OVA cells. Established tumors were irradiated (20 Gy) on day 10 after tumor inoculation. Tumor-bearing mice were intratumoral injected with 2 μmol of NaBu on day 1 after IR. Tumors were harvested, and CD11c⁺ cells were sorted and cocultured with OT-I CD8⁺ T cells for analysis of their T cell activation ability in an ELISPOT assay. Unpaired t tests were used to analyze the other data. *, P < 0.05; **, P < 0.01. One representative experiment (out of two experiments) is shown.