TCR^–/– → F1 bone marrow chimeras have normal responses to KLH after host cells contribute to T-cell differentiation. TCR^—/— → F1 (▨), B6 → F1 (▦) bone marrow chimeras, and normal CB6F1 mice (▪) were primed with KLH/CFA in the hind footpads; 8 to 10 days later, T-cell recall responses were measured as described in “Materials and methods.” Each bar represents one mouse, black bars represent CB6F1, gray bars represent B6 → F1, and hatched lines represent TCR^—/— → F1 mice. Results are representative of 2 independent experiments.