Isolation of C-reactive protein from cat serum

C-reactive protein (CRP) was isolated from sera from healthy cats by calcium-dependent affinity chromatography on phosphorylcholine derivatives of bovine albumin-coupled Toyopearl, followed by an anion-exchange chromatography using DEAE cellulose. It was identified as CRP by its immunochemical cross reactivity with human CRP. The molecular weight of cat CRP was approximately 100 kilodaltons (kDa) and composed of two glycosylated subunits (23 kDa) and three non-glycosylated subunits (20 kDa) with non-covalent association. Under electron microscopic examination, cat CRP had a pentameric disc-like configuration which is characteristic of CRP. Immunoelectrophoresis and isoelectric focusing showed that cat CRP is an acidic α₁-globulin (pi 4-1 to 4-3). Serum concentrations of CRP in cats and kittens were measured by single radial immunodiffusion. In 12 healthy cats from various sources, values ranged from 38 to 168 μg/ml. In kittens, serum CRP levels also showed a wide distribution, 81 per cent of them were less than 40 μg/ml.