HA presentation by hematopoietic cells in the periphery of TCR-HAxIg-HA but not in TCR-HAxpgk-HA mice. (A) CD11c⁺ and CD19⁺ cells were electronically sorted from Ig-HA and pgk-HA mice, and different amounts of cells were tested for their capacity to induce HA-specific proliferation in vitro. Peptide (p, 0.1 μg/mL) was added in 1 condition as positive control. (B) CD4⁺6.5⁺ cells from a Thy1.1 TCR-HA mouse were CFSE-labeled and transferred (1 × 10⁶) into Balb/c, Ig-HA, or pgk-HA recipients. Balb/c mice reconstituted 7 weeks before with pgk-HA bone marrow (last column) were also used as recipients. Three days after transfer, the proliferation of CD4⁺Thy1.1⁺ cells in the lymph nodes was determined by flow cytometry. Representative dot plots are shown, and the percentage of Thy1.1⁺ cells within the CD4⁺ gate is indicated. Two mice per group and 2 independent experiments were performed with similar results.