The acute phase protein serum amyloid A (SAA) as a marker of inflammation in horses

Acute phase proteins such as serum amyloid A, haptoglobin, and alpha 1-acid glycoprotein have been identified as markers of inflammation in cattle because they are produced by the liver in response to pro-inflammatory cytokines. This study was designed to assess whether they could be used to discriminate between acute and chronic inflammation. Their concentrations were measured in serum samples from 81 cattle in which inflammation was classified by thorough clinical examination, supported by postmortem findings, as being acute in severity in 31 and chronic in 50. The classical haematological markers of inflammation were also determined in blood from the animals. Serum amyloid A had a maximum (100 per cent) clinical sensitivity in discriminating between the acute and chronic cases, and haptoglobin had the highest clinical specificity of 76 per cent; counts of neutrophils and band neutrophils had sensitivities of 71 per cent and 42 per cent and specificities of 30 per cent and 72 per cent, respectively. It was concluded that serum amyloid A and haptoglobin may be used to discriminate between acute and chronic inflammatory conditions.

The concentrations of the acute-phase proteins, serum amyloid-A (SAA) and haptoglobin (Hp), were determined in the plasma of healthy cows (n = 25) and cows with spontaneous acute (n = 6), subacute (n = 37), or chronic (n = 7) inflammatory diseases. The plasma concentration of SAA alone, Hp alone, and the Hp/SAA ratio, differed significantly (p < 0.001) between healthy animals and animals with inflammatory diseases. Plasma Hp concentrations in the group of cows with acute inflammatory diseases were significantly (p < 0.01) different from those in the group with chronic inflammatory diseases. Moreover, the Hp/SAA ratio in chronic inflammatory diseases was significantly different from this ratio in acute (p < 0.01) and subacute (p < 0.05) inflammatory diseases. It is therefore concluded that the plasma concentrations of SAA and Hp and the Hp/SAA ratio are useful parameters to distinguish healthy animals from animals with inflammation and can be helpful in distinguishing between acute and chronic of inflammatory diseases.

The acute-phase reactant rabbit serum amyloid A 3 (SAA3) was identified as the major difference product in Ag-induced arthritis in the rabbit, a model resembling in many aspects the clinical characteristics of rheumatoid arthritis (RA) in humans. In Ag-induced arthritis, up-regulated SAA3 transcription in vivo was detected in cells infiltrating into the inflamed joint, in the area where pannus formation starts and, most notably, also in chondrocytes. The proinflammatory cytokine IL-1beta induced SAA3 transcription in primary rabbit chondrocytes in vitro. Furthermore, rSAA3 protein induced transcription of matrix metalloproteinases in rabbit chondrocytes in vitro. In the human experimental system, IL-1beta induced transcription of acute-phase SAA (A-SSA; encoded by SAA1/SAA2) in primary chondrocytes. Similar to the rabbit system, recombinant human A-SAA protein was able to induce matrix metalloproteinases' transcription in chondrocytes. Further, immunohistochemistry demonstrated that A-SAA was highly expressed in human RA synovium. A new finding of our study is that A-SSA expression was also detected in cartilage in osteoarthritis. Our data, together with previous findings of SAA expression in RA synovium, suggest that A-SAA may play a role in cartilage destruction in arthritis.