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Quantitative and qualitative properties of host polymorphonuclear cells during experimentally induced Staphylococcus
M J Daley1, E R Oldham, T J Williams
1Agricultural Research Division, American Cyanamid Co, Princeton, NJ 08540.
Abstract:
Polymorphonuclear cells have a critical role in the pathogenesis of bovine mastitis. We have documented that experimentally induced Staphylococcus aureus mastitis is associated with cyclic increase and decrease in the quantity of viable bacteria shed in the milk. Concomitant with this cycling of bacteria is an inverse cycling of the hosts cells within the milk. Such somatic cells were determined to be greater than or equal to 95% polymorphonuclear cells. The quality of these cells was evaluated by measuring their relative efficiency of bacterial killing and phagocytosis at various times during an infection. Host polymorphonuclear cells had as much as 10,000-fold variation in the bactericidal failure rate for staphylococci during cell cycling. The most efficient bactericidal effect was observed at or near the peak of the somatic cell count (SCC). The ability of these cycling cells to ingest fluorescent beads was also quantitated by use of flow cytometry. The percentage of phagocytic polymorphonuclear cells that ingested fluorescent latex beads ranged from 15 to 80% of the total cell population during cell cycling, and tended to be optimal at or near peak SCC. In addition, the average number of beads ingested varied between 1 and 2 particles/polymorphonuclear cell, with as many as 17% of the phagocytic cells ingesting 4 or more beads at maximal efficiency. Polymorphonuclear cells from quarters infected with S aureus varied quantitatively (total SCC) and qualitatively (bactericidal activity and phagocytic ability) during the course of an infection. Not only is the quantity of host's phagocytic cells in the mammary gland central to the defense mechanism against infection, but the biological activation state appears to be equally important. The role of these cells in the pathogenesis of a cycling infection is presented in a model to explain the cyclic nature of mastitis.
Insights
Bovine mastitis involves cyclic changes in Staphylococcus aureus bacteria and host polymorphonuclear cells. These immune cells show variable bacterial killing and phagocytosis, peaking with high somatic cell counts (SCC).
Area of Science:
- Veterinary Immunology
- Bacterial Pathogenesis
- Bovine Health
Background:
- Bovine mastitis is a significant economic disease in dairy cattle.
- Polymorphonuclear cells (PMNs) are crucial for combating mammary gland infections.
- Staphylococcus aureus is a common causative agent of bovine mastitis.
Purpose of the Study:
- To investigate the quantitative and qualitative changes in host polymorphonuclear cells during Staphylococcus aureus-induced bovine mastitis.
- To correlate the functional capacity of PMNs (bactericidal and phagocytic activity) with somatic cell count (SCC) dynamics.
- To propose a model explaining the cyclic nature of mastitis based on immune cell behavior.
Main Methods:
- Experimentally induced Staphylococcus aureus mastitis in cows.
- Quantification of viable bacteria shed in milk.
- Enumeration and functional assessment (bactericidal assays, phagocytosis of fluorescent beads) of milk somatic cells, primarily PMNs.
- Flow cytometry used to measure phagocytic activity.
Main Results:
- Cyclic increases and decreases in bacteria were inversely correlated with PMN numbers in milk.
- PMN bactericidal failure rate for staphylococci varied up to 10,000-fold during infection.
- Optimal PMN bactericidal and phagocytic activity (ingestion of beads) occurred near peak SCC, with percentages ranging from 15-80% phagocytic cells.
Conclusions:
- Both the quantity and functional state (activation) of PMNs are critical in controlling S. aureus mastitis.
- The cyclic nature of mastitis can be explained by the fluctuating quantitative and qualitative responses of host PMNs.
- Understanding PMN dynamics offers insights into host defense mechanisms against bovine mastitis.