Efficacy of a bovine Staphylococcus aureus vaccine using interleukin-2 as an adjuvant

The purpose of this study was to examine the efficacy of a vaccination protocol using recombinant bovine interleukin-2 (rBoIL-2) as an adjuvant with a Staphylococcus aureus vaccine. Holstein dairy cows were immunized with a S. aureus vaccine in conjunction with either saline solution (n = 3), Freund's incomplete adjuvant (FIA; n = 3) or rBoIL-2 (n = 3). Whey and serum were analysed for antibody titer to specific S. aureus antigens. Isolated blood mononuclear cells (BMC) were examined for their ability to proliferate and to produce interleukin-2 (IL-2) and interferon (IFN) after either mitogenic or antigenic stimulation in vitro. Efficacy of the vaccination protocols was assessed by challenging experimental animals intramammarily with 100 colony forming units of S. aureus. Regardless of treatment, all cows exhibited similar serum antibody titers to S. aureus pseudocapsule. Cows treated with saline exhibited a significant increase in serum alpha-toxin antibody titer when compared to levels observed in FIA and rBoIL-2-treated cows. However, cows receiving rBoIL-2 treatment exhibited significantly higher lacteal pseudocapsule antibody titer compared to the other adjuvant groups. Administration of rBoIL-2 did not enhance BMC proliferative responses to the mitogens concanavalin A (ConA), phytohemagglutinin (PHA), pokeweed mitogen (PWM) or interleukin-2 (IL-2) when compared to FIA or saline treated cows. Although cows receiving rBoIL-2 treatment exhibited enhanced cytokine production upon antigenic stimulation, efficacy of the vaccination protocol was inferior compared to the protection offered by saline treatment.