Abstract
Interleukin-2, pokeweed mitogen, and lipopolysaccharide were evaluated for their ability to accelerate involution and to stimulate local cellular defenses in the nonlactating bovine mammary gland. Twelve cows were divided into three treatment groups of 4 cows each to receive interleukin-2, pokeweed mitogen, or lipopolysaccharide. One day after drying off, 3 mammary quarters of each cow were infused with 100µg of immunostimulant daily for 21 d; the remaining control quarter received PBS. Secretion samples were collected weekly to determine bacteriologic status, total SCC, and differential cell counts. On d 21, cows were killed, and tissues were collected for microscopy. Overall, SCC were higher in immunostimulated quarters, but only those infused with interleukin-2 were significantly elevated over controls. By wk 3, the percentage of neutrophils decreased in interleukin-2 and pokeweed mitogen quarters over pretreatment values, percentage of macrophages increased in interleukin-2 quarters, and percentage of lymphocytes increased in pokeweed mitogen and lipopolysaccharide quarters. Percentage of alveolar lumina was reduced, and connective tissue stroma increased, in all immunostimulated quarters compared with those of controls, suggesting accelerated involution. Involution was greatest in quarters treated with interleukin-2. Leukocyte infiltration was greater in immunostimulated quarters than in control quarters. Similarly, concentrations of Ig-producing plasma cells were greater in immunostimulated quarters than in control quarters. Quarters infused with interleukin-2 exhibited the greatest concentration of plasma cells, followed by quarters treated with pokeweed mitogen and lipopolysaccharide; IgG1 plasma cells predominated, followed by IgG2, IgA, and IgM. Interleukin-2 accelerated involution and stimulated local antibody production more than did the two mitogens, suggesting a potential role for this cytokine as a general immunostimulant at drying off.
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