More viral peptide–MHC complex available to T cells in Ly49H⁻ mice sustains ongoing T cell proliferation. Ly49H⁻ and Ly49H⁺ mice were infected with 5 × 10³ PFU of MCMV-K181-HA and APC populations enriched by density gradient and negative antibody enrichment on day 2, 4, and 6 pi. (A) The phenotype and frequency of the enriched populations is shown. Density plots (gated on live lymphocytes) depict the CD11c and Siglec H expression in Ly49H⁻ and Ly49H⁺ mice. (B) APCs were enriched from MCMV-K181-HA infected Ly49H⁻ and Ly49H⁺ mice, as shown in A, at day 0, 2, 4, and 6 pi, and incubated in vitro with CFSE-labeled Tg-HA CD8⁺ T cells for 5 d. Histograms show proliferation of CD8⁺ T cells (gated on live, TCR⁺, CD8⁺, and CD4⁻). CD8⁺ T cells incubated with uninfected APCs are shown as gray-filled histograms. CD8⁺ T cells incubated with APC from 2, 4, and 6 d pi are shown as solid black lines. The frequencies of cells with diluting CFSE are shown. Data are representative of two independent experiments performed in triplicate. All experiments were performed in BALB.B6-CT6 (Ly49H⁻) and BALB.B6-CT8 (Ly49H⁺) mice.