L-selectin expression on thymocytes of BM chimeras. After irradiation, normal (A-B) and L-selectin-deficient (C-D) C57BL/6 mice were reconstituted with syngeneic bone marrow cells collected from normal (A,C) or L-selectin-deficient (B,D) mice, as described in “Materials and methods.” After 6 weeks, the thymocytes were analyzed for L-selectin expression by flow cytometry using the MEL-14 mAb antibody (dark line). Control included incubation with the PE conjugate alone.