Growth promotion in chickens by interleukin-2

Chicken interleukin-2 (cIL-2), which was prepared by sensitizing chicken lymphocytes with concanavalin A, was administered to fertile broiler eggs on Day 18 of embryonation (0.1 mg in 200 mL distilled water). Controls (CON) received distilled water. Hatched chicks were reared to 6 wk. Body weight (BW), as well as abdominal fat pad, liver, bursa of Fabricius, a thymic lobe, spleen, and gonads were excised and expressed relative to BW at 2, 4, and 6 wk of age. Additionally, hematocrit (HCT), hemoglobin (HGB), and plasma protein (PP) levels were determined at the three time intervals. Finally, chicks were sensitized against human gamma globulin (HGG) and challenged at 6 wk by intradermal injections into the wattles. Delayed type hypersensitivity (DTH) to HGG was used as a direct measure of cell-mediated immunity. In ovo cIL-2 increased BW consistently, relative fat pad weights at 2 wk, relative bursa and liver weights at 2 and 6 wk, HBG and relative thymic weight at 2 and 4 wk, and PP at 2 wk. Delayed type hypersensitivity to HGG was not affected by cIL-2. Potential metabolic and immunologic mechanisms to explain in ovo cIL-2 effects are discussed.