Expression of LT-βR and its ligands. (A) D5 tumor cells were first stained with monoclonal rat anti-mouse LT-βR antibody (kind gift from Dr. M. Croft, La Jolla Institute for Allergy and Immunology) and isotype control antibody, and then with FITC-labeled goat anti-rat IgG (Jackson immune research laboratory). After staining, cells were analyzed by flow cytometry. D5 alone, filled histogram; isotype, dashed line; anti-mouse LT-βR, solid line. Effector T cells that were not stimulated (B) or stimulated with anti-CD3 and CD28 antibodies for 6 hours (C) were incubated with mouse LT-βR-Fc fusion protein or control Fc fusion protein (509-Fc), and stained with PE-labeled goat anti-human Fc antibody. Stained cells were analyzed by flow cytometry. Solid line, control Fc fusion protein; dashed line, LT-βR Fc fusion protein.