Circulating immune complexes of Aβ and IgM in plasma of patients with Alzheimer's disease

Abstract

It has previously been shown that immune complexes (IC) of a given biomarker with class M immunoglobulins (IgM) provide better performances compared to the unbound biomarker in a number of cancer entities. In the present work, we investigated IC of IgM-Aβ as a potential biomarker for Alzheimer's disease (AD). Aβ-IgM concentration has been measured in 75 plasma samples from patients with AD, individuals with mild cognitive impairment (MCI), and healthy age- and sex-matched controls (HC). To characterize the fractions associated with Aβ, pooled plasma samples were subjected to gel-filtration analysis. Size-separated fractions were analyzed for the presence of Aβ using a sandwich ELISA assay. A strong reactivity was observed in the high molecular weight IgM (>500 kDa) and 150 kDa (IgG) fractions indicating that blood Aβ is strongly associated with antibodies. Using an ELISA assay detecting Aβ-IgM complexes, we observed that high levels of Aβ-IgMs were detectable in HC and MCI patients; however, there was no significant difference to the AD group. © 2009 Springer-Verlag.