Development of multilineage chimerism after simultaneous BM plus SITx, but not after BM infusion or SITx alone, in BN-to-LEW combination under short-course TAC immunosuppression. (A) Flow cytometric analysis of blood chimerism with mAbs for donor MHC class I. Transplantation of intestine alone (n = 10) showed an early high-level chimerism at day 14. Donor cells gradually decreased and disappeared at day 120. After BM cell injection alone (n = 6), donor cells gradually increased with a peak (2% to 6%) at day 40, slowly decreased, and became undetectable by day 90. On the contrary, when BM and intestine were transplanted together (n = 12), augmented macrochimerism (3% to 10%) was maintained for 150 days. *P < .05 versus BM or SITx alone. (B) B-cell–dominant multilineage chimerism was seen in both host spleen and intestinal graft MLNs 150 days after BM infusion plus SITx. Donor cells were not identified in recipients of BM or SITx alone; n = 3 to 7 for each group. *P < .05 versus BM or SITx alone. N/D indicates not detected; N/A, not applicable. (C) Representative flow cytometry of the blood taken at day 150 from 1 of the recipients of BM plus intestine transplantation. Result demonstrates multilineage macrochimerism, including donor T, B, and NK cells and macrophages. (D) Double fluorescent immunohistochemical staining of host spleen with OX27 (BN MHC class I, red) and anti–rat IgM (B cell, green). Abundant OX27-positive donor cells were found in the B-cell area of the spleen at day 150 after BM infusion plus SITx but not after SITx alone (40×/0.75 numeric aperture [NA] oil-immersion objection). Images are representative of 3 animals per group.