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In vitro study of polymorphonuclear leukocyte damage to mammary tissues of lactating cows
Abstract:
Effects of polymorphonuclear neutrophil leukocytes (PMN) on mammary tissue of lactating cows were studied in vitro. The PMN were isolated from mammary glands of nulliparous heifers given an injection of 5 micrograms of Escherichia coli endotoxin. Mammary tissue was obtained from noninfected quarters of 5 lactating Holstein cows and was cultured in supplemented medium 199. Mammary explants were treated by addition of intact or lysed PMN (10(5), 10(6), 10(7)/ml) or PMN (10(5), 10(7)/ml) which were allowed to phagocytose opsonized zymosan. Controls included cultures of mammary tissue alone, PMN alone, and mammary tissue plus zymosan. Cultures were incubated at 37 C for 3, 8, or 24 hours. Tissue from 1 randomly selected culture/treatment was weighed and processed for microscopy. Tissue from remaining cultures was incubated with [3H]amino acids or [14C]acetate to determine rates of protein and fatty acid synthesis. Media from all cultures were assayed for activity of the lysosomal enzyme, N-acetyl-beta-D-glucosaminidase. An increase (P less than 0.02) in the activity of this enzyme was detected in the medium of explant cultures treated with 10(7) phagocytosing PMN/ml at 3 and 8 hours and with 10(7) intact or lysed PMN/ml at 8 hours. Treatment did not inhibit (P greater than 0.05) rates of protein or fatty acid synthesis. Microscopic examination indicated that epithelial cell damage resulted from treatment with 10(6) and 10(7) intact, lysed, or phagocytosing PMN/ml. Greatest morphologic damage resulted from treatment with phagocytosing PMN.
Insights
Polymorphonuclear neutrophils (PMN) can damage mammary tissue in lactating cows, especially when phagocytosing. However, PMN exposure did not significantly inhibit protein or fatty acid synthesis in this in vitro study.
Area of Science:
- Veterinary Medicine
- Cell Biology
- Biochemistry
Background:
- Mammary gland health is crucial for milk production in lactating cows.
- Polymorphonuclear neutrophils (PMN) are immune cells involved in inflammation.
- Understanding PMN interactions with mammary tissue is important for managing mastitis.
Purpose of the Study:
- To investigate the in vitro effects of PMN on mammary tissue explants from lactating cows.
- To assess the impact of different PMN treatments (intact, lysed, phagocytosing) on tissue morphology and function.
Main Methods:
- Mammary tissue explants from Holstein cows were cultured.
- Explant cultures were treated with various concentrations of PMN (intact, lysed, phagocytosing zymosan).
- Tissue morphology, lysosomal enzyme activity (N-acetyl-beta-D-glucosaminidase), and synthesis of protein and fatty acids were assessed.
Main Results:
- Increased lysosomal enzyme activity was observed with high concentrations of PMN, particularly phagocytosing PMN.
- Epithelial cell damage occurred at higher PMN concentrations, with the most significant damage from phagocytosing PMN.
- Protein and fatty acid synthesis rates were not significantly inhibited by PMN treatments.
Conclusions:
- PMN, especially those actively phagocytosing, can cause significant morphologic damage to bovine mammary epithelial cells in vitro.
- Despite causing damage, PMN did not inhibit essential metabolic functions like protein and fatty acid synthesis under the experimental conditions.
- These findings contribute to understanding the cellular mechanisms of mammary tissue damage during inflammation.