The bound proteins were eluted by a stepwise increase of NaCl from 50 to 500 mm. The fractions with good absorbance selleckchem at 280 nm were analysed by SDS-PAGE and Western blot. The primary antibody (goat anti-human C3) was used at 1 : 500 dilutions (3-h incubation), and the secondary antibody and rabbit anti-goat–horseradish peroxidase conjugate were used at a 1 : 500 dilutions (for 2 h). The fractions with apparent good purity (125 mm elutes) were pooled, dialysed against the equilibration buffer and rechromatographed as before. The purity of recovered C3 was >95% as judged by the densitometry of Coomassie Blue-stained

gel. The coupling of C3 to CNBr-activated Sepharose was performed essentially as described for other proteins [16]. Equal volume (150 μL) of adult H. contortus extract or ES products was mixed with purified C3 and kept at 4°C for 12–16 h. To this, 20 μL of anti-human C3 antibody was added and further incubated at 4°C for 8–10 h. The suspension Erlotinib cell line was centrifuged at

10 000 g at 4°C in a microfuge. The supernatant was discarded, and the pellet was washed three times with PBS and analysed by SDS-PAGE electrophoresis. The H.c-C3BP was first isolated from the ES products collected from 900 to 1000 adult worms using C3–Sepharose as an affinity matrix. The ES products were filtered and passed through a C3–Sepharose column equilibrated with 20 mm Tris-HCl (pH 7·4) and 100 mm NaCl. The column was washed with excess buffer, and the bound proteins were eluted with 0·2 m glycine–HCl (pH 2·2), immediately neutralized with 1 m Tris and analysed by SDS gel electrophoresis. The same protocol enough was followed for the isolation of H.c-C3BP from the adult H. contortus. The frozen worms were transferred to a

mortar kept in an ice bucket and homogenized with a solution containing 20 mm Tris-HCl (pH 7·4), 100 mm NaCl, 2·0 mm EDTA and 1 mm PMSF. The homogenate was centrifuged at 10 000 g for 30 min at 4°C. The supernatant was decanted and filtered before chromatography. The H.c-C3BP interaction with C3 was also studied on a microtitre plate (F96 Maxisorp, Nunc, Denmark) where the wells were coated with 100 μL of 10 μg/mL of purified C3BP in carbonate–bicarbonate buffer (100 mm, pH 9·6) at 4°C overnight. Wells were emptied and washed with saline. The free sites on the plastic surface were blocked with 100 μL of gelatin (10 mg/mL in PBS) for 90 min at room temperature. Uncoated wells and those coated with C3 protein were also blocked. In control C3 wells, highest concentration of C3 (2 μg/mL) was used for coating the wells followed by blocking with gelatin. After washings with PBS-T, different dilutions of C3 protein in PBS (0·25–2 μg/mL) were added to H.c-C3BP-coated wells. The plate was incubated for 3–4 h at room temperature followed by washings. Goat anti-human C3 antibody was added at 1 : 1500 dilutions in PBS-T (100 μL/well).