Serum antibodies from DTA-1–treated animals transfer anaphylactic activity to naive mice. (A-E) C57BL/6J mice were treated with 1 mg DTA-1 or isotype control (rat IgG2b, clone LTF-2) on days −10 and −6. On day 0, mice were euthanized, and sera, spleens, and lymph nodes were removed. Either (B) 50 × 10⁶ cells from pooled spleens and lymph nodes or (C-E) 200 µL pooled sera were transferred by intravenous tail vein injection into naive (C,D) C57BL/6J or (E) GITR^−/− mice. Three hours later, a single dose of DTA-1 was administered by intraperitoneal injection, and rectal temperatures were monitored for 1 hour, represented by individual lines in the graphs. Data are representative of 3 independent experiments (n = 5 mice per group). (F-G) Donor mice were treated as in (A). After sera were harvested, antibodies were fractionated from the pooled sera by using a protein A/G column. Either (F) 1 mg of the antibody fraction or (G) 11 mg of the antibody-depleted fraction (termed “flowthrough” fraction) was transferred by intravenous tail vein injection into naive mice. Three hours later, 1 mg DTA-1 was administered by intraperitoneal injection, and rectal temperatures of individual mice were monitored, represented by individual lines in the graphs. Data are representative of 2 independent experiments (n = 3 to 5 mice per group).