The supernatants of TT-specific B cell clones were further tested for their capacity to recognize different antigens by ELISA. We observed that IgM mAbs did not cross-react with unrelated antigens (i.e., HBsAg and respiratory syncytial virus (RSV) antigens) ( Figure 4A) . The TT-specific B cell clones were also screened by flow cytometry for direct binding of the TT antigen labeled with a fluorochrome ( Figure 4B) . Interestingly, three types of clones that produced antibodies that gave a similar signal in ELISA were detected, with high, intermediate and low binding of the fluorescent TT antigen.