The effect of α2 macroglobulin in commercial cytokine assays

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Abstract

α2 macroglobulin (α2M), a 725 kDa plasma protein, has been reported to bind a range of cytokines. We have therefore investigated its effect on a number of commercial cytokine assays. The methylamine converted fast form of the molecule was found to reproducibly depress, by 26% or more, the standard curves obtained with certain commercial assays for IL-2 and for tumor necrosis factor α, and had a small inhibitory effect on some IL-4 assays. In contrast it slightly enhanced or had no effect on ELISAs for IL-1β and IL-6. The inhibition observed was directly proportional to the concentration of α2M used in the range 0.5–5 mg/ml. Studies in the IL-2 system also revealed that it was largely attributable to the fast form of α2M. Preliminary evidence suggests that the effects observed may be dependent on the assay source. These findings may be relevant to the assay of biological fluids in which α2M is present.

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