Letter Regarding Article by Li et al, “C-Reactive Protein Upregulates Complement-Inhibitory Factors in Endothelial Cells”
To the Editor:
Recently, Li et al reported an increase in decay accelerating factor (DAF) expression on human endothelial cells on incubation with C-reactive protein (CRP).1 Using our in-house–generated recombinant CRP,2 we were unable to reproduce these effects on human umbilical vein endothelial cells or the endothelial cell line EA.hy926. Commercial CRP (recombinant, Calbiochem), however, increased DAF expression on both cell types. Commercial CRP preparations contain 0.05% to 0.1% azide per milligram CRP. When azide was removed by dialysis, the commercial CRP lost its ability to induce DAF (Figure). When azide was added to our own CRP, this preparation gained the ability to increase DAF expression (see Figure). Azide on its own also increased DAF expression significantly (see Figure). We obtained similar results with EA.hy926 and human umbilical vein endothelial cells. The commercial CRP preparation (Trichem Resources) used by Li et al also contains azide (0.1%/mg CRP). These authors did not mention the removal of the azide before the addition of CRP to the cells. We show here convincingly that azide, present in commercial CRP preparations, is responsible for the increased expression of DAF, and therefore conclude that the results published by Li et al are artifacts and must be attributed to azide and not to CRP. Furthermore, CRP-induced endothelial cell activation studies with commercial preparations of CRP must be interpreted with care because some of the components in these preparations may induce artifacts. Indeed, we have found recently that azide and not CRP is responsible for the reported CRP-induced vasorelaxation.2
The authors’ research on this topic received financial support from the British Heart Foundation.
Li SH, Szmitko PE, Weisel RD, Wang CH, Fedak PW, Li RK, Mickle DA, Verma S. C-reactive protein upregulates complement-inhibitory factors in endothelial cells. Circulation. 2004; 109: 833–836.
van den Berg CW, Taylor KE, Lang D. C-reactive protein-induced in vitro vasorelaxation is an artefact caused by the presence of sodium azide in commercial preparations. Arterioscler Thromb Vasc Biol. 2004; 24: e168–e171.