Antigen-Sepharose conjugate preparation: 5 mg of antigen was dissolved in 1 mL of coupling buffer (0.1 M NaHCO 3 containing 0.5 M NaCl, pH 8.0). The CNBr-sepharose 4B (Amersham Bioscience AB, Uppsala, Sweden) was activated by swelling in 1 mM HCl and then washed with coupling buffer. The antigen solution was added to the gel and the mixture was stirred for 1h at RT. After the coupling reaction, excess antigen was washed away with coupling buffer. The unreacted activated groups were blocked by treatment with ethanolamine (0.25 M; pH 8.0) for 30 min at RT. The gel was then washed with sodium acetate buffer (0.1 M; pH 4.0), followed by coupling buffer. The antigensepharose beads were either used or stored at 4uC in PBS (1x) containing 1 mM azide.