Stx consists of a cytotoxic A subunit and a pentamer of cell-binding B subunits [9]. The A subunit inhibits protein synthesis due to its N-glycosidase activity, which removes an adenine base from 28S ribosomal RNA and induces apoptotic cell death [9], [10]. The B subunits bind to cell surface carbohydrate selleck chemical CHIR99021 ligands like globotriaosylceramide (Gb3), which is also known as CD77 in human activated B-lymphocytes [11], [12]. CD77 is expressed on some Burkitt��s lymphoma cell lines and germinal center B cells in humans, but not on mouse germinal center B cells [13]�C[15]. Gb3 is also expressed on Vero cells, which are derived from the kidneys of African green monkeys, and Stx exhibits cytotoxicity toward Vero cells [16].

Immunoglobulin A (IgA) is one of the major factors for immune defense against pathogens and toxins on mucosal surfaces such as that of the intestines [17]. On the mucosal surface, IgA is secreted as SIgA consisting of dimeric IgA (dIgA), comprising two IgA monomers covalently linked through a joining (J) chain, and a secretory component (SC). By binding with SC, IgA gains resistance to digestive enzymes and the ability to be localized near the epithelial surface through anchoring to the mucus [18]�C[20]. Thus, SIgA is supposed to function well in the protection of the gastrointestinal tract. Based on this function, SIgA is expected to prevent infectious diseases by excluding the entry of toxic substances and pathogens from the gastrointestinal tract when used as an orally administered therapeutic antibody.

Production of therapeutic antibodies using mammalian cell cultures has limitations due to the high cost and limited scalability of production [21], [22]. A plant expression system is expected to be a candidate for solving these problems because of the lower cost of production and higher scalability [21]�C[25]. Plants are also suitable as hosts for the production of edible pharmaceutical proteins [26]�C[28]. EHEC can be transmitted by fruits and vegetables contaminated with the faeces of domestic or wild animals [29]. Thus, physical containment is required, but this is naturally a part of the production process for transgenic plants. Because it does not require sterile syringes and health professionals, the oral administration of therapeutic proteins will be particularly useful in developing countries.

If Stx-specific SIgA can be expressed in plants, therapeutic or preventive effects would be expected in people eating these Carfilzomib plants expressing recombinant antibodies. Recombinant antibodies produced by plants have been proposed to be called ��plantibodies�� [23]. In previous studies, we established mouse hybridoma cell lines producing IgA and IgG monoclonal antibodies (mAb) against Stx1B [30], [31]. Of the two, the IgG mAb more efficiently inhibited Stx1B binding to cell surface ligands.