A NEW ASSAY FOR THE INVASIVE ADENYLATE-CYCLASE TOXIN OF BORDETELLA-PERTUSSIS BASED ON ITS MORPHOLOGICAL EFFECTS ON THE FIBRONECTIN-STIMULATED SPREADING OF BHK-21-CELLS

When baby hamster kidney (BHK) cells are allowed to spread on fibronec tin-coated substrata in the absence of serum and the presence of agent s which elevate intracellular 3':5'-cyclic AMP (cAMP) levels they adop t an abnormal, stellated morphology. To determine whether the invasive adenylate cyclase (AC) toxin of Bordetella pertussis induced the same response, cell extracts were prepared from several B. pertussis strai ns. They were characterized for AC toxin production by enzymic assay a nd by immunoblotting with an AC-toxin-specific monoclonal antibody. Ex tracts of strains producing AC toxin induced elevated levels of intrac ellular cAMP in BHK cells and promoted a stellation response during ce ll spreading. Extracts prepared from strains defective in AC toxin pro duction showed no effect. Using image analysis to quantify the morphol ogical change, we have demonstrated that the effect of AC toxin on cel l spreading is dose dependent. This technique is a rapid and sensitive assay for the invasive AC toxin.