Host cells contribute specifically to the T-cell lineage in TCR^–/– → F1 bone marrow chimeras. Bone marrow cells from T-cell–deficient mice were used to reconstitute normal CB6F1 recipients as described in “Materials and methods.” (A) The staining profile of one representative mouse is shown. Reconstitution of blood lineages was assessed starting at 3 months after transfer, by antibody staining of lymph node and spleen cells with anti-Thy-1 antibodies (biot-J1j) for T-cell–lineage identification, PE–anti-CD19 for B-cell–lineage identification together with anti–class I antibodies specific for H-2D^d molecules (FITC-34-4-21S). (B) Myeloid lineages were analyzed by staining peritoneal cavity cells with anti–H-2K^b (right panels) or anti–H-2K^d (left panels) antibodies. Representative staining profiles for one mouse from each group (TCR^—/— → F1 and B6 → F1, broken lines) are shown. Staining of normal F1 mice with each antibody is depicted by solid lines.