Matters arising.

Systemic inflammation in osteoarthritis Several studies have shown that the acute phase response may take place in osteoarthritis (OA), suggesting that low grade systemic inflammation may be present in patients with OA. 1 2 I read with interest the paper by Stürmer et al on high sensitivity C reactive protein (CRP) in relation to the severity and extent of OA. 3 As assessed by high sensitivity nephelometry, serum high sensitivity CRP was higher in 770 patients with advanced OA than in 567 age and sex matched healthy controls (geometric mean 2.5 mg/l v 1.7 mg/l, respectively). Moreover, severity of pain as measured by a visual analogue scale was associated with mean high sensitivity CRP. Interestingly, neither the bilateral nor the generalised extent of OA, nor any of the dimensions of the Western Ontario and McMaster Universities OA index (WOMAC) were associated with mean high sensitivity CRP concentrations. The authors concluded that the subjective severity of pain is associated with low level systemic inflammation in OA, and measurement of high sensitivity CRP may have some potential for monitoring and/or predicting the clinical course of OA. In contrast with CRP, some acute phase proteins like a 1-acid glycoprotein (AGP) or a 1-antichymotrypsin (ACT) are glycoproteins and possess glycosylation sites attached by N-glycosidically bound, complex-type oligosac-charide side chains. 4 Heteroglycans of acute phase proteins share the common core structure but differ in their outer chain sequences. According to the number of these oligosac-charide chains bi-, tri-and tetra-antennary heteroglycans can be distinguished. This structural diversity (termed ''microhetero-geneity'') results in different reactivity with the lectin concanavalin A (con A). It has been shown that biantennary side chains react strongly with con A. Thus, diverse micro-heterogeneous forms of acute phase glyco-proteins, containing different number of biantennary heteroglycans, differ in their reactivity with con A. 5 Glycosylation of acute phase proteins takes place in the liver and is controlled by cytokines. 6 Affinity immunoelectrophoresis with con A is a simple technique that can be used to study the glycosylation pattern of acute phase proteins. 7 Glycosylation variants of AGP/ACT can be separated during electrophoresis in a gel containing con A, and the area enclosed by the precipitates representing microhetero-geneous variants of AGP and ACT can be measured by planimetry (fig 1). The results are usually expressed as the reactivity coefficients (AGP RC and ACT RC, respectively), calculated according to the formula: total area under the peaks of …