Hepatic immune response in calves during acute subclinical infection with bovine viral diarrhoea virus type 1

Eight colostrum-deprived calves aged 8–12 weeks were inoculated intranasally with a non-cytopathic strain of bovine viral diarrhoea virus (BVDV) genotype-1 and the effects on the hepatic immune response were studied. Two calves were sacrificed at each of 3, 6, 9 and 14 days post-inoculation (dpi) and two uninoculated animals were used as negative controls. BVDV was detected in hepatic macrophages and monocytes from 3 to 14 dpi and in Küpffer cells (KCs) from 6 to 14 dpi. Increases in the numbers of MAC387+ KCs and monocytes, but not interstitial macrophages, differentiated by morphological features, were evident in the liver following inoculation with BVDV. There was a substantial increase in the number of monocytes positive for tumour necrosis factor (TNF)-α, but only small increases in the numbers of TNF-α+ KCs and interstitial macrophages and interleukin (IL)-6+ monocytes, KCs and interstitial macrophages. There was an increase in the number of interstitial CD3+ T lymphocytes in the liver, but no substantial changes in the numbers of circulating CD3+ T lymphocytes, interstitial or circulating CD4+ or CD8+ T lymphocytes, or CD79αcy+ B lymphocytes. Serum haptoglobin and serum amyloid A increased transiently at 12 dpi. Upregulation of some pro-inflammatory cytokines by hepatic macrophages is evident in subclinical acute BVDV type 1 infection in calves.