Antibody penetration achieving

Clostridial neurotoxins are very toxic. However they are ineffective in individuals immunized with the corresponding toxoids. In most countries children are vaccinated with tetanus toxoid and this is sufficient to provide full protection against tetanus for decades. A booster injection of tetanus toxoid (available from health authorities) before starting research with TeTx is advisable. On the other hand, the vaccine for BoNT/A, B, C, D and E is not commercially available, but can be obtained from the Center for Disease Control (CDC, Atlanta, GA). Due to the rather low efficacy of the BoNTs vaccine, a protective serum anti-BoNT titre is generally, but not always, achieved. Human anti-TeTx antibodies and horse anti-BoNT antibodies are also available from health authorities, and their injection immediately after accidental penetration of the toxin into the circulatory system is sufficient to prevent the disease. 

For antibodies to penetrate inside fixed cells, the membranes must be opened with detergents. Membranes are lipid bilayers that have a hydrophilic or water-soluble side facing the cytoplasm and the extracellular space (Fig. 5.4a). The hydrophobic or water-insoluble sides face each other at the center of the membrane. Also, there are transmembrane proteins that interact with the lipids and are held in the membrane. Membranes are barriers because they do not allow water or hydrated molecules to pass. For immunocytochemistry, the membrane must be parhally dissolved to allow antibodies to cross. It is also important that the transmembrane proteins remain cross-linked to other proteins so that they are not washed away (Fig. 5.4b). Detergent will dissolve the membranes but not the transmembrane proteins, which are cross-linked by the fixative to other proteins (e.g., scaffold proteins). For tissue sections, antibodies must penetrate through many cell layers into the center of the section. Achieving this depth of penetration requires removing most of the cell membranes but leaving the proteins so that they can bind antibodies when needed. 

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