Sn⁺ macrophage-mediated presentation of MHC class I-restricted peptide of β-gal (A) and processing of β-gal protein and presentation of MHC class I-restricted peptide (B) to CD8 T lymphocytes. Immune spleen lymphocytes (responder cells) from DBA/2 mice primed 9 days before by intrapinna injection of a subtumorigenic dose of lac Z gene-transfected ESb-L cells were depleted of macrophages and DCs by plastic adherence and incubated with SPL (□), Sn⁺ spleen macrophages (◊; 2 × 10⁷responder and 2 × 10⁶ stimulatory cells), or DCs (▾; 2 × 10⁷ responder and 2 × 10⁴ stimulatory cells). The incubation mixture also contained β-gal whole antigen (B) or its derived MHC class I-restricted peptide (TPHPARIGL) (A). In some cultures, anti-Sn blocking MoAbs (1C2 and SER-4) were added (★). Negative controls included responder cells and Sn⁺ cells without the antigen (○) or antigen with responder cells only (▴). Five days later, the stimulation cultures were harvested and the cytotoxic activity of generated effector cells (E) was tested in a 4-hour⁵¹Cr release assay using as target cells (T) the lac Z-transduced P815 mastocytoma cell line, P13.1. Means and standard deviations from 4 independent experiments are shown. Data points without SD represent values for which the SD was smaller than 1.