Delayed-type hypersensitivity reactions. (A) Contact hypersensitivity reactions to oxazolone in IL-3–deficient (□) and wild-type littermates (▪). Values (n = 5) are mean ± SEM: C57BL/6, P = .025; BALB/c, P = .014. (B) Fibrin deposition during contact hypersensitivity to oxazolone (C57BL/6 background). P < .001 for oxazolone challenge. Plasma values for ¹²⁵I-labeled fibrinogen 24 hours after injection were 1,948 ± 61.7 for +/+ mice and 1,879 ± 53.3 cpm for −/− animals. (C) Tumor protection in immunized female IL-3–deficient (▵) and wild-type littermates (○) (BALB/c background). Wild-type controls, no vaccine (□). All surviving animals at day 55 were tumor free. Pooled results from two independent experiments (10 mice per group). (D) Delayed-type hypersensitivity to irradiated tumor cells inoculated in the footpads of immunized female IL-3–deficient (□) and wild-type littermate mice (▪) (BALB/c background).