A method for isolating the bioactive component of the water-soluble extract of Uncaria tomentosa known as C-MED-100.RTM., comprising (i) precipitating the spray drying carrier from C-MED-100.RTM.; (ii) using the resulting C-MED-100.RTM. to obtain a spotting mixture for thin layer chromatography (TLC); (iii) spotting the C-MED-100.RTM. spotting mixture on pre-run TLC plates and eluting the plates to obtain the fluorescing band with R.sub.f=0.2-0.3; (iv) scraping off the R.sub.f=0.2-0.3 band, eluting it in ammonia and freeze drying the eluted band to form a powder; and (v) extracting the powder with methanol to remove solubilized silica gel, concentrating the methanol solution and crystallizing the concentrated solution to obtain the bioactive component. The isolated bioactive component in vitro is a quinic acid analog, preferably quinic acid lactone. By contrast, the isolated bioactive component in vivo is quinic acid, whether as free acid or as a quinic acid salt, including quinic acid ammonium salt. A pharmaceutical composition comprising a pharmaceutically effective amount of the bioactive component and a nontoxic inert carrier or diluent. The bioactive component may be used to enhance immune competency, treat disorders associated with the immune system, inhibit the inflammatory response, treat disorders associated with the inflammatory response, enhance the anti-tumor response, and treat disorders associated with the response to tumor formation and growth, all in mammals.