IL-6 and soluble IL-6R levels are increased during GVHD. (A-B) Lethally irradiated (900 cGy) Balb/c mice received a transplant of Balb/c BM (10 × 10⁶) and spleen cells (0.4-0.5 × 10⁶, syngeneic) or B6 BM (10 × 10⁶) and an equivalent number of B6 spleen cells (allogeneic). Cohorts of animals (n = 5-9/group) were killed weekly and serum was analyzed for IL-6 and soluble IL-6R levels using either Bioplex or enzyme-linked immunosorbent assay as described in “Cytokine analysis.” Values for normal control mice that did not undergo transplantation (n = 5) are depicted. Data are derived from 2 independent experiments. (C-D) RNA was extracted from spleen, liver, and colon tissues obtained from recipients of syngeneic or allogeneic marrow grafts (n = 7-8 mice per tissue) at the indicated time points, and gene expression of IL-6 (C) and total IL-6R (D) was analyzed by real-time q-PCR as described in “Real-time q-PCR.” Values for normal control mice that did not undergo transplantation (n = 5-6 mice/tissue) are depicted. Data are derived from 2 independent experiments and are presented as the mean ± SEM. (Statistics: *P ≤ .05, **P < .01.)