| Summary: | <p>Abstract</p> <p>Background</p> <p>Caseous lymphadenitis (CLA) is a disease of small ruminants caused by <it>Corynebacterium pseudotuberculosis</it>. The pathogenesis of CLA is a slow process, and produces a chronic rather than an acute disease state. Acute phase proteins (APP) such as haptoglobin (Hp) serum amyloid A (SAA) and α<sub>1 </sub>acid glycoprotein (AGP) are produced by the liver and released into the circulation in response to pro-inflammatory cytokines. The concentration of Hp in serum increases in experimental CLA but it is not known if SAA and AGP respond in parallel or have differing response profiles.</p> <p>Results</p> <p>The concentration in serum of Hp, SAA and AGP in 6 sheep challenged with 2 × 10<sup>5 </sup>cells of <it>C. pseudotuberculosis </it>showed significant increases (P < 0.05) compared to 3 unchallenged control sheep. By day 7 post infection. (p.i.) the Hp and SAA concentrations reached mean (± SEM) values of 1.65 ± 0.21 g/L and 18.1 ± 5.2 mg/L respectively. Thereafter, their concentrations fell with no significant difference to those of the control sheep by day 18 p.i.. In contrast, the serum AGP concentration in infected sheep continued to rise to a peak of 0.38 ± 0.05 g/L on day 13 p.i., after which a slow decline occurred, although the mean concentration remained significantly higher (P < 0.05) than the control group up to 29 days p.i.. Specific IgG to phospholidase D of <it>C. pseudotuberculosis </it>became detectable at 11 days p.i. and continued to rise throughout the experiment.</p> <p>Conclusion</p> <p>The serum concentrations of Hp, SAA and AGP were raised in sheep in an experimental model of CLA. An extended response was found for AGP which occurred at a point when the infection was likely to have been transforming from an acute to a chronic phase. The results suggest that AGP could have a role as a marker for chronic conditions in sheep.</p>
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