EFFECTS OF INTERLEUKIN-1 AND INTERLEUKIN-2 ON MAMMARY-GLAND LEUKOCYTEPOPULATIONS AND HISTOLOGY DURING THE EARLY NONLACTATING PERIOD

Eight Jersey cows free of intramammary infection (IMI) with major mast itis 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 secretion s were collected 7 days prior to drying off, at drying off, and on day s 1, 2, 3, 4, 7, and 14 of the nonlactating period. Cows were slaughte red and mammary tissues were collected at 7 (3 cows) and 14 (5 cows) d ays after treatment. The infusion of 10 mu g of IL-1 produced an eleva tion in rectal temperature that was significantly higher than that of cows receiving IL-2 or PBS at 4, 5, and 6 hours after treatment, where as cows receiving 1.0 mg of IL-2 exhibited no change in rectal tempera ture. 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 i n IL-2-treated glands. The mammary involution process was accelerated by IL-2, and tissues exhibited reductions in alveolar epithelial and l uminal areas and increases in connective tissue stroma and degree of l eukocytosis compared with IL-1 and control glands. Concentrations of p lasma cells producing IgG(1), IgG(2), 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 an d in accelerating involution during the early nonlactating period.