Pro-inflammatory cytokine and acute phase protein responses to low-dose lipopolysaccharide (LPS) challenge in pigs

The objective of this study was to establish the pro-inflammatory cytokine and acute phase protein responses to low-dose lipopolysaccharide (LPS) challenge in pigs and to determine whether these immune parameters could also be measured in saliva. Possible gender differences in the acute phase reaction were also assessed. At 6 weeks of age, 24 male and 24 female pigs were injected intraperitoneally with a single dose of 0 or 5 μg/kg live weight (LW) of LPS fromEscherichia coli(treatment). Matched saliva and blood samples were taken at 0, 2, 4, 8, 12 or 24 h after treatment administration. Samples were analysed for concentrations of the pro-inflammatory cytokines tumor necrosis factor-alpha (TNF-α) and interleukin-1beta (IL-1β), the acute phase proteins C-reactive protein (CRP), serum amyloid A (SAA), haptoglobin (Hp), and cortisol. Low-dose LPS administration increased plasma levels of TNF-α (P<0·001), CRP (P<0·05) and SAA (P<0·05) but did not affect plasma concentrations of IL-1β or Hp (P>0·1). Treatment by time interactions showed that plasma levels of TNF-α and CRP in LPS-treated pigs peaked at 2 h (P<0·001) and 12 h (P<0·01), respectively. Low-dose LPS injection tended to increase plasma concentrations of cortisol (P=0·056) and the response to LPS differed between genders (P<0·05), with females showing higher cortisol responsiveness to the challenge (P<0·01). Males showed higher levels of both cytokines regardless of the treatment (P<0·05), probably due to the inhibition of cytokine synthesis by cortisol. Concentrations of both pro-inflammatory cytokines were consistently detectable in saliva and were present in higher concentrations than in plasma (P<0·001). Hence, plasma TNF-α, CRP and SAA are useful indicators of sub-acute inflammation/infection in pigs as simulated by a low-dose LPS challenge and gender differences exist in the pro-inflammatory cytokine response after a low dose of LPS.