Effects of hyperimmune equine plasma on clinical and cellular responses in a low-dose endotoxaemia model in horses

Endotoxaemia is a major cause of equine morbidity, and plasma from horses immunised against Escherichia coli is used in its treatment. The aim of this study was to determine the effects of hyperimmune plasma on the clinical and leukocyte responses, including production and activity of TNFα, in an in vivo endotoxin challenge model. Pre-treatment with hyperimmune equine plasma had no significant effect on peak total plasma TNFα concentration (occurring 90 min after the administration of 30 ng/kg LPS). However, the bioavailable (unbound) TNFα measured by bioassay was significantly reduced in plasma-treated horses (1044.44 ± 193.93 pg/ml at 90 min) compared to saline treated controls (1373.92 ± 107.63 pg/ml; P = 0.05). Therefore, although pre-treatment with hyperimmune equine plasma did not significantly modify the clinical signs of endotoxaemia in this model, there was some evidence of reduced TNF bioactivity, which may be due to factors in the plasma which bind and reduce the activity of this cytokine.