TCRβ^−/− and CD154^−/− mice do not produce antidonor Ab, but only CD154^−/− reject skin graft. BALB/c (H-2^d) skin grafts were transplanted onto TCRβ^−/− and CD154^−/− mice (H-2^b). At 5 to 7 weeks after the first skin graft, a second BALB/c skin graft was transplanted onto each mouse. Wild-type B6 (H-2^b) mice served as controls. (A) Life table analysis of first skin graft survival. All animals were followed up to 120 days. MST was 12.4 (± 2.0) days for CD154^−/− and 12.0 (± 2.4) days for wild-type B6 recipients and more than 120 days for TCRβ^−/− mice. (B) Sera were collected 4 weeks after first and second skin grafts. Sera collected before the first skin graft served as a control. Sensitization was measured by FCXM assay on sera obtained at selected time points. Levels of circulating alloantibodies were determined by FACSCalibur, gating on the CD4⁺ and CD8⁺ T-cell fraction, and were reported as mean fluorescence intensity (MFI). Antidonor Ab titers were tested in TCRβ^−/− and CD154^−/− mice as well as B6 controls before placement of the donor skin graft (naive sera) or at 4 weeks after first and second skin graft. Data are presented as averages plus or minus SD. (C) Life table analysis of second BALB/c skin graft survival.