Hybridoma cell lines were screened by an indirect ELISA. The cell lines producing specific antibodies were recloned successively 3-7 times by limiting dilution to ensure monoclonality and stability of the cell line. Hybridoma cell lines were then propagated in large 175 cm 2 tissue culture flasks, and the conditioned supernatant collected. Purification of IgG mAbs was achieved by affinity chromatography using Protein G agarose (Sigma, USA). The IgG immunoglobulin subclass was determined using the mouse hybridoma isotyping reagents according to instructions from the manufacturer (Sigma, USA).