Western blot analysis of transgenic N. tabacum plants expressing MAb 2G12. Leaf discs from 2G12-expressing plants were extracted in either PBS (-) or PBS supplemented with protease inhibitor cocktail (+) and incubated at room temperature for 24 hours. Proteins were separated by 4-15% SDS-PAGE under non-reducing conditions. The proteins were blotted to nitrocellulose membranes and probed with either anti-human IgG Fc-specific antiserum (Panel A) or anti-human κ antiserum (Panel B). The positive control (PC) consists of the human IgG1κ (1 ng/lane). The asterisk indicates the fully assembled 2G12 antibody; lower case letters (a to i) indicate antibody fragments.