Effect of recombinant bovine interleukin-8 (rbIL-8) on health, metabolism, and lactation performance in Holstein cattle I: Production and functional characterization of rbIL-8 in vitro and in vivo.

In the present study, we standardized processes of cloning and purification of recombinant bovine interleukin-8 (rbIL-8) from bacterial culture and assessed its biological activity in Holstein cattle. Plasmid containing a subclone of bovine IL-8 was expressed using Escherichia coli BL21 and cell lysate was purified by chromatography. The presence of rbIL-8 was assessed by Western blot analyses and function was confirmed in vitro using a chemotaxis chamber. Based on optical density values, chemoattractant properties of rbIL-8 were 10-fold greater compared with control wells. Two in vivo studies were conducted to assess the biological activity of rbIL8. For study 1, one-year-old Holstein heifers (n = 20) were randomly allocated to receive a single intravaginal administration containing 1,125 µg of rbIL-8 diluted in 20 mL of saline solution (rbIL-8, n = 10) or a single intravaginal administration of 20 mL of saline solution (control, n = 10). For study 2, nonpregnant lactating Holstein cows (n = 31) were randomly allocated to receive an intrauterine administration with 1,125 µg of rbIL-8 diluted in 20 mL of saline solution (rbIL-8, n = 11), a positive control consisting of resin-purified lysate of E. coli BL21 not transfected with the plasmid coding for rbIL-8 diluted in 20 mL of saline solution (E. coli, n = 10), and a negative control administered with 20 mL of saline solution (control, n = 10). An increase in vaginal neutrophils was observed in heifers treated with rbIL-8 within 3 h of treatment, but not in control heifers. Additionally, intrauterine administration of rbIL-8 increased the proportion of PMN cells in uterine cytological samples from 3.5% before treatment to 75.8% 24 h later—an increase that was not observed in the negative control group and cows treated with resin-purified lysate of E. coli. To further evaluate the effect of local and systemic rbIL-8 stimulation on the dynamics of circulating white blood cells, a third study was conducted. In study 3, nonpregnant 8-mo-old Holstein heifers (n = 30) were randomly allocated into 1 of 3 treatment groups: intravenous rbIL-8 (1,125 µg of rbIL-8 diluted in 5 mL of saline solution, n = 10); intravaginal rbIL-8 (1,125 µg of rbIL-8 diluted in 20 mL of saline solution; n = 10); or intravaginal saline (20 mL of saline solution, n = 10). Intravenous injection of rbIL-8 resulted in a transient increase in rectal temperature, which was greater at 2 h after treatment compared with cows treated intravaginally with rbIL-8 or heifers treated with saline solution. Heifers treated with rbIL-8 intravenously displayed a marked reduction in neutrophils, basophils, lymphocytes, and monocytes within the first 4 h posttreatment compared with heifers treated intravaginally. However, at 6 h after treatment, heifers treated with rbIL-8 intravenously displayed a rebound in white blood cell counts caused by an increase in neutrophil counts. These results show that the presented purification method is effective and results in biologically active rbIL-8 that can be used safely to modulate immune responses in cattle.