3.

Control of allo-IgM (a) or allo-IgG (b) responses in BALB/c recipients receiving C57BL/6 heart grafts and treated with anti-CD154 plus DST (filled squares) or untreated (empty squares). Sera were harvested on the indicated days posttransplantation. (c-e) Tolerant BALB/c mice (>day 60 post-first transplant) were challenged with second C57BL/6 hearts and transfused with 1.5 × 10⁶ 3-83 B cells (Tol). A group of naive BALB/c mice receiving the first C57BL/6 heart and 3-83 B cells served as positive controls (Naïve), while untransplanted BALB/c mice receiving 3-83 B cells only served as negative controls (Control). Sera were harvested on the indicated days post-second heart transplant and infusion of 3-83 B cells (c-e). The levels of anti-C57BL/6 IgM (a,c) and IgG (b,d) were quantified at a 1:10 serum dilution by flow cytometry, and the 3-83 idiotypic (Id) IgM levels (diluted 1:10) were determined with an anti-idiotypic ELISA (e). Data are presented as the mean channel fluorescence (MCF) (a-d) or mean optical density (O.D.) (e) ± standard error of mean (N=8/group).