T-cell lymphopenia in conditional Crry gene knockout mice depends on systemic complement. (A) Bone marrow cells from CD4-Cre⁻-Crry^flox/flox and CD4-Cre⁺-Crry^flox/flox mice were transplanted into lethally irradiated C3^−/− recipients. After 2 months, total thymus cellularity and CD4⁺, CD8⁺ T-cell numbers and percentages in the thymi, spleens, lymph nodes, and blood of the 2 types of chimeras (n = 4 per group) were analyzed as in Figure 4. No difference was detected between the 2 types of chimeras. Values are mean plus or minus SEM. (B) Flow cytometry analysis of Crry expression and C3 deposition on thymocytes of chimera mice. CD4-Cre⁻-Crry^flox/flox → C3^−/− chimeras had normal Crry expression on thymocytes, whereas CD4-Cre⁺-Crry^flox/flox → C3^−/− chimeras had no thymocyte Crry expression nor C3 deposition. (C) FACS analysis of Crry and DAF expression on thymocytes (left) and splenic CD4⁺ T cells (right) in CD4-Cre⁻-Crry^flox/flox (denoted as −) and CD4-Cre⁺-Crry^flox/flox (denoted as +) mice. DAF is not expressed on thymocytes, and average DAF level on surviving splenic CD4⁺ T cells in CD4-Cre⁺-Crry^flox/flox mice (denoted as +) was higher than that on splenic CD4⁺ T cells of CD4-Cre⁻-Crry^flox/flox mice (denoted as −). (D) FACS analysis of Crry and DAF expression on thymocytes (left) and splenic CD4⁺ T cells (right) in CD4-Cre⁻-Crry^flox/flox → C3^−/− (denoted as −) and CD4-Cre⁺-Crry^flox/flox → C3^−/− (denoted as +) chimeras. No difference in DAF expression was detected on splenic CD4⁺ T cells of the 2 groups of mice in this case.