A large, distinct population of CD3^-CD5⁺ cells exists in D^d-ζ transgenic mice. (A) Fresh splenocytes were stained with mAbs to CD3 and CD5 and examined by flow cytometry. The percentage of CD3^–CD5⁺ cells for each strain is indicated. (B) In a similar experiment, cells were also stained with anti-D^d mAb (34-2-12), and the positive cells (histograms) were gated, as indicated, into D^d high and D^d low populations. (C) CD3 versus CD5 expression on the D^d high splenocytes (top panels) and D^d low expressing cells (bottom panels).