Methods for reducing nonspecific interaction in antibody–antigen assay via atomic force microscopy

We developed a method to measure the rupture forces between antibody and antigen by atomic force microscopy (AFM). Previous studies have reported that in the measurement of antibody–antigen interaction using AFM, the specific intermolecular forces are often obscured by nonspecific adhesive binding forces between antibody immobilized cantilever and substrate surfaces on which antigen or nonantigen are fixed. Here, we examined whether detergent and nonreactive protein, which have been widely used to reduce nonspecific background signals in ordinary immunoassay and immunoblotting, could reduce the nonspecific forces in the AFM measurement. The results showed that, in the presence of both nonreactive protein and detergent, the rupture forces between anti-ferritin antibodies immobilized on a tip of cantilever and ferritin (antigen) on the substrate could be successfully measured, distinguishing from nonspecific adhesive forces. In addition, we found that approach/retraction velocity of the AFM cantilever was also important in the reduction of nonspecific adhesion. These insights will contribute to the detection of specific molecules at nanometer scale region and the investigation of intermolecular interaction by the use of AFM.


Epigallocatechin activates haem oxygenase-1 expression via protein kinase Cδ and Nrf2

The Nrf2/anti-oxidant response element (ARE) pathway plays an important role in regulating cellular anti-oxidants, including haem oxygenase-1 (HO-1). Various kinases have been implicated in the pathways leading to Nrf2 activation. Here, we investigated the effect of epigallocatechin (EGC) on ARE-mediated gene expression in human monocytic cells. EGC time and dose dependently increased HO-1 mRNA and protein expression but had minimal effect on expression of other ARE-regulated genes, including NAD(P)H:quinone oxidoreductase 1, glutathione cysteine ligase and ferritin. siRNA knock down of Nrf2 significantly inhibited EGC-induced HO-1 expression. Furthermore, inhibition of PKC by Ro-31-8220 dose dependently decreased EGC-induced HO-1 mRNA expression, whereas MAP kinase and phosphatidylinositol-3-kinase pathway inhibitors had no significant effect. EGC stimulated phosphorylation of PKCαβ and δ in THP-1 cells. PKCδ inhibition significantly decreased EGC-induced HO-1 mRNA expression, whereas PKCα- and β-specific inhibitors had no significant effect. These results demonstrate for the first time that EGC-induced HO-1 expression occurs via PKCδ and Nrf2.