Anti-idiotype monoclonal antibodies (Mabs) to mLL2, an anti-B-cell lymphoma and CD22-specific murine IgG2a-kappa Mab, were generated by hybridoma technology from splenocytes of Copenhagen rats immunized with mLL2 F(ab')2. Mab WN, an IgG2a-kappa, was selected based on its specific binding to mLL2 and not other IgG isotypes or anti-B-cell Mabs. In a radioimmunoassay, WN was found to inhibit the binding of 125I-labeled mLL2 to Raji cells and to have no effect on the binding of other B-cell-reactive antibodies. Using high performance liquid chromatography analysis, WN was shown to complex specifically with both mLL2 and mLL2 Fab'. Meanwhile, we have constructed chimeric (cLL2) and humanized (hLL2) versions of LL2. Both cLL2 and hLL2 were demonstrated to retain the original antigen specificity and affinity of mLL2 [S.O. Leung et al., Proc. Am. Assoc. Cancer Res., 2872 (abstract), 34: 481, 1993]. The specific binding of WN to either radioiodinated or peroxidase-conjugated mLL2 was inhibited in a dose-response manner, and to a similar extent by mLL2, cLL2, and hLL2. Since the mLL2 complementarity-determining regions are the only sequences common to mLL2, cLL2, and hLL2, the result confirms that WN is specific to the antigen-binding complementarity-determining regions. A WN binding assay is currently being evaluated as a substitute for the tedious, and sometimes inconsistent, Raji cell-binding assay for the determination of LL2 immunoreactivity. In conclusion, we have developed an anti-idiotype Mab, WN, to mLL2. Its potential use as a surrogate antigen for B-cell lymphoma is under investigation.