Toxicity tests on native and recombinant Bordetella pertussis adenylate cyclase toxin preparations

Bordetella pertussis produces a cell-invasive adenylate cyclase toxin which is synthesised from the cyaA gene as an inactive protoxin that is post-translationally activated by the product of the cyaC gene. Active and inactive CyaA proteins were prepared in crude and purified form from B. pertussis or from recombinant E. coli expressing both cyaA and cyaC genes or the cyaA gene alone, respectively. The specific AC activities of all the crude or all the purified toxins were similar. The toxins produced in the absence of CyaC activity had no cell invasive, haemolytic or cytotoxic activity. The cell invasive and cytotoxic activities of native and recombinant active CyaA preparations were similar, but the haemolytic activity of the recombinant toxin was lower than that of the native protein. As part of mouse protection tests, mice were injected subcutaneously with 15 microg per mouse of crude or purified CyaA preparations plus alhydrogel or with 1/5 human dose of adsorbed DPT vaccine (Wellcome Trivax-AD) using two doses at a two week interval. Control groups of mice were injected with alhydrogel in PBS alone or left unvaccinated. The toxin preparations had little or no effect on mouse weight gain, and there were no marked differences between mice vaccinated with the active toxin and those given the inactive form. Thus, at the dose used, there was no clear toxic physiological response caused specifically by active CyaA.