HSCs express MHC class II. (A-B) B cells (CD19⁺; A) and HPCs (lin⁻c-kit⁺; B) were sorted from non-Tg (C57BL/6) and MII.OVA mice and mRNA isolated. Relative levels of MHC class II (I-A_β^b) and OVA mRNA were determined by TaqMan qPCR. Data are mean ± SD of 3 separate cell preps assayed twice for each sample. (C) BM was harvested from WT (C57BL/6, dotted line) and IA^b.EGFP (solid line) mice and analyzed by flow cytometry to define lin⁻c-kit⁺ HPCs, long-term HSCs (LT-HSCs), common myeloid progenitors (CMPs), granulocyte/macrophage progenitors (GMPs), and megakaryocyte/erythroid progenitors (MEPs) using the gating strategy shown. B cells (CD19⁺, dark line) and DCs (CD11c⁺, gray line) were gated from spleen cell suspensions and compared with wild-type B cells (dashed line). Data are representative of 3 to 5 mice analyzed in parallel in 2 separate experiments.