CYTOLOGIC RESPONSES OF STAPHYLOCOCCUS AUREUS-INFECTED MAMMARY-GLANDS OF HEIFERS TO INTERFERON-GAMMA AND INTERLEUKIN-2 TREATMENT

Cytologic and bacteriologic responses, and changes in cytokine activit y were evaluated in secretions of Staphylococcus aureus-infected mamma ry glands after treatment of heifers with recombinant bovine interfero n gamma (rbIFN gamma) or interleukin 2 (rbIL-2). Two groups of 4 heife rs each, experimentally infected with 10(7) colony-forming units (CFU) of S aureus, were injected in 2 quarters via the teat canal, with 10( 5) U of rbIFN gamma (trial 1) or 7.5 x 10(5) U of rbIL-2 (trial 2) 2 w eeks after experimentally induced infection; control quarters received phosphate-buffered saline solution. Mammary secretion samples were ta ken on days O, 1, 2, 3, 4, 7, and 14 after cytokine infusion. Secretio ns were diluted 1:10 and used to perform somatic cell counts (SCC), di fferential cell counts, and CFU enumerations, and to determine the num ber of leukocytes expressing major histocompatibility complex class-II (MHC II) antigens. In addition, mammary secretion samples taken on da ys 0, 1, and 2 were processed to obtain skimmed milk for evaluation of rbIFN gamma- and rbIL-2-like activities. Treatment with rbIFN gamma d id not influence SCC, or differential or bacteria counts, or the numbe r of leukocytes expressing MHC II antigens. However, rbIL-2 stimulated leukocytosis, which may have reduced bacteria counts early in the tri al; treatment with this cytokine also increased the neutrophil, macrop hage, lymphocyte, and eosinophil counts in secretions. Similarly, numb ers of MHC II-positive leukocytes were greater in rbIL-2-treated quart ers vs controls. Compared with day 0, IFN gamma-like activity was incr eased on only day 1 in both trials. Interleukin-2-1ike activitywas not influenced in the rbIFN gamma trial, but was increased on days 1 and 2 in the rbIL-2 trials. Results indicated that neither cytokine may ha ve had a major influence on the course of established S aureus infecti ons. However, the increased SCC in rbIGL-treated quarters may have acc ounted for the reduction in CFU throughout the trial after treatment w ith this cytokine. Greatest cytokine-like activity was observed on day 1; howe the consequences of cytokine activity, such as the sustained eosinophilia after rbIL-2 treatment, were detected over the 14-day tri al period, indicating possible prolonged action.