Influence of interleukin-1 on neutrophil function and resistance to Streptococcus suis in neonatal pigs

Nonspecific immunity is usually lower in neonates than adults. Consequently, enhancing the neonate's nonspecific immune capability may be beneficial for the health and growth performance of young animals. We conducted two experiments in which neonatal pigs were injected with recombinant bovine interleukin-1 beta (rBoIL-1 beta) at 9 to 11 days of age. Three consecutive daily injections of rBoIL-1 beta increased neutrophil and monocyte numbers, which remained elevated until the animals were challenged with Streptococcus suis at 19 days of age. Neutrophil bactericidal activity was greater in interleukin-1-treated pigs than in saline-injected controls. At lower ratios of effector to target cells, neutrophil-mediated, antibody-dependent cellular cytotoxicity was increased in neonates treated with IL-1. However, natural killer cell activity and neutrophil production of superoxide anion were not affected by treatment with IL-1. Expression of CD18 was increased transiently on neutrophils from IL-1-treated pigs at 15 days of age. Severity of the streptococcal infection was less in pigs that were treated with IL-1 at 9 to 11 days of age. These data suggest that IL-1 treatment in neonates may augment nonspecific immune function and disease resistance.