Binding and cytotoxic effects of Clostridium botulinum type A, C1 and E toxins in primary neuron cultures from foetal mouse brains.

Binding of purified Clostridium botulinum type A, C1 and E toxins to cultured cells was studied by an immunocytochemical method. Type A and C1 toxins bound strongly to neuron cultures prepared from brains of foetal mice, but binding of type E toxin was weak. None of the toxin types bound to the feeder layer, composed of non-neuronal cells. The heavy-chain component of the type C1 toxin bound to neurons, but the light chain component did not. Type C1 toxin also bound only to cell lines of neuronal origin. When type C1 toxin [final concentration 4 x 10(2) LD50 (10 ng) per well] was added to primary neuron cultures in 96-well plates, degeneration of neuronal processes and rounding of neuronal somas were observed, but type A and E toxins did not produce such changes. The binding and cytotoxic activities of type C1 toxin were blocked by heat treatment (80 degrees C for 30 min) or by preincubation of the toxin with polyclonal anti-C1 IgG and some of the monoclonal antibodies which neutralized the toxin activity in mice. In the neuronal processes treated with C1 toxin, many degenerated mitochondria, membranous dense bodies and vesicles were observed by electron microscopy; these ultrastructural changes were similar to those of Wallerian degeneration in vivo.