TBI rapidly depletes host APCs and induces IL-10 transcription in host B cells. (A) Absolute numbers of splenic DCs, B cells, and non-B, non-DC cells prior to and at 24 hours and 72 hours after TBI. Results are expressed as mean ± SE of 3 to 5 individual animals. (B) IL-10 copy number (normalized to B2M) in DCs, B cells, and non-B, non-DC populations prior to and at 24 and 72 hours after TBI. Results are expressed as mean ± SE of replicate samples from 3 experiments in which B cells (CD19⁺/class II⁺), DCs (CD11c⁺/class II⁺), or non-B, non-DC (CD19^–/class II^–) were FACS sorted from the spleen of 2 to 5 animals at various times after TBI. UD indicates undetected. (C) Intracellular staining of IL-10. Splenocytes from control (top panels) or irradiated wild-type B6 mice, 24 hours after TBI with 1000 cGy (bottom panels) were stained as described in “FACS and cytokine analysis.” Proportion of IL-10–positive B cells was determined in MHC class II (I-A/I-E)⁺/CD19⁺ population. Representative plots from 1 of 2 identical experiments shown.