Production of anti-Gal by memory anti-Gal B cells. (A) Production of anti-Gal IgG in irradiated KO mice undergoing the following treatments: adoptive transfer of 20 × 106 spleen lymphocytes from PKM-immunized KO mice and 2 PKM immunizations, the first of which was given 14 days (•), 1 month (▴), 2 months (▪), or 3 months (♦) after adoptive transfer, or no PKM immunization and serum obtained on day 14 after adoptive transfer (▵); adoptive transfer of 20 × 106 spleen lymphocytes from naive KO mice and 2 PKM immunizations, the first of which was given 14 days (○), or 3 months (⋄) after adoptive transfer. Data are from 2 representative mice in each group of 5 mice. (B) Anti-Gal production in recipients of 5 × 106 B lymphocytes expressing cell-surface IgG from PKM-immunized mice and of 5 × 106 T cells from naive KO mice (○) or 5 × 106 primed T cells from KO mice immunized 3 times with PKM (•). Mice were immunized twice with PKM, starting on day 14 after adoptive transfer. Note that memory anti-Gal B cells expressing IgG can be activated by PKM in the presence of either naive or primed T cells.