Effects of yeast expressed recombinant interleukin-2 and interferon-gamma on physiological changes in bovine mammary glands and on bactericidal activity of neutrophils

The physiological effects of intramammary infusions of recombinant bovine c ytokines in six lactating dairy cows on the quality and yield of milk and t he bactericidal activity of milk neutrophils were investigated. Recombinant bovine interleukin-2 (rboIL-2) and interferon-gamma (rboIFN-gamma) were pr oduced in the yeast Pichia pastoris. Two animals were given rboIL-2 (2 x 10 (6) units) in two quarters, two animals were given rboIFN-gamma (85 x 10(5) units) in two quarters, and the other two cows received a dose of rboIL-2 in one quarter and rboIFN-gamma in a second quarter. In addition, each anim al was given phosphate-buffered saline (PBX) in the other two quarters as a control. Somatic cell counts and conductivity of the fore milk were monito red before and after infusion. Neutrophils were isolated from quarter milk samples 36 h after infusion of cytokine or PBS and their bactericidal activ ities against Staphylococcus aureus were measured in vitro with a colorimet ric assay. Quarters infused with rboIL-2 or rboIFN-gamma showed significant but transitory increases in both milk somatic cell counts and conductivity when compared with preinfusion values and with control quarters. There wer e minimal effects on daily milk yield. Neutrophils isolated from milk from quarters infused with rboIL-2 showed enhanced bactericidal activity against Staph. aureus. The bacterial killing from rboIL-8 treated quarters was sig nificantly greater, with a mean of 63.5% compared with a mean of 5.4 % for neutrophils takes from uninfected quarters to which PBS had been administer ed. The bactericidal activities for quarters treated with rboIFN-gamma and infected quarters treated with PBS were 15.0 and 30.0% respectively. The re sults indicate that intramammary infusions of rboIL-8 and rboIFN-gamma to l actating cows are well tolerated, and that rboIL-2 can activate milk neutro phils and augment their bactericidal activity.