Effects of interleukin-1 and interleukin-2 on mammary gland leukocyte populations and histology during the early nonlactating period.

Eight Jersey cows free of intramammary infection (IMI) with major mastitis pathogens were intramammarily infused with interleukin (IL)-1, IL-2, or phosphate-buffered saline (PBS) after the last milking prior to drying off. Rectal temperatures were monitored hourly through 6 hours after infusion and at 24-hour intervals thereafter. Quarter secretions were collected 7 days prior to drying off, at drying off, and on days 1, 2, 3, 4, 7, and 14 of the nonlactating period. Cows were slaughtered and mammary tissues were collected at 7 (3 cows) and 14 (5 cows) days after treatment. The infusion of 10 micrograms of IL-1 produced an elevation in rectal temperature that was significantly higher than that of cows receiving IL-2 or PBS at 4, 5, and 6 hours after treatment, whereas cows receiving 1.0 mg of IL-2 exhibited no change in rectal temperature. Somatic cell counts (SCC) in mammary glands infused with IL-1 or IL-2 remained significantly elevated over PBS-infused control glands through day 4 after treatment. Neutrophils predominated in secretions of IL-1-treated glands, and macrophages and lymphocytes predominated in IL-2-treated glands. The mammary involution process was accelerated by IL-2, and tissues exhibited reductions in alveolar epithelial and luminal areas and increases in connective tissue stroma and degree of leukocytosis compared with IL-1 and control glands. Concentrations of plasma cells producing IgG1, IgG2, IgA, and IgM also were greatest following IL-2 infusion. Results suggest that IL-2 is superior to IL-1 in stimulating an increase in mammary mononuclear cell populations and in accelerating involution during the early nonlactating period.