The flow cytometry evidence of antibody reactivity with antigens on the surface of IEs expressing VSAPAM and the absence of reactivity with non-PAM-type VSA (Table 1) was confirmed by immunofluorescence microscopy of live IEs ( Fig. 2D and E). Denaturing Western blots of the VSAPAM-expressing sublines yielded single, distinct bands (of similar size for each antibody) when probed with PAM3.10, PAM5.2, PAM6.1 and PAM7.5 monoclonal antibodies ( Fig. 2F , and data not shown). Proteins were not detected when blots were probed with the monoclonal antibodies PAM1.4, PAM2.8 or PAM4.7 (data not shown) despite their reactivity with the surface of intact VSAPAMexpressing IEs (Table 1) , pointing to reactivity with conformation-dependent epitopes. No bands were observed when the monoclonal antibodies were used to probe Western blots of the non-PAM-type VSAexpressing parental lines (Fig. 2F , and data not shown).