Science Cannabis

196 THE SCIENCE OF MARIJUANAwhite blood cells present. White cells are the soldiers of the immunesystem, they are attracted to regions of tissue inflammation or damageand help to kill and remove infectious microbial invaders and to removedamaged or dead cells and tissue debris. The large white cells known asmacrophages are particularly important scavengers, which engulf and killinvading bacteria and fungi and remove damaged tissue. Approximately2-3 times more macrophages were collected from the lungs of tobaccoor marijuana smokers versus nonsmokers, suggesting the presence of aninflammatory response. The macrophage from both tobacco and marijuanasmokers also showed significant impairments in their ability to killand engulf fungi (Candida albicans) or bacteria (Staphylococcus aureus).The macrophages from smokers were also less able to generate some ofthe chemical toxins (e.g., superoxide) that they normally use to kill invadingmicroorganisms, or the chemicals known as cytokines that help toactivate further inflammatory and immune system responses. In addition,the macrophages were impaired in their ability to attack and kill cancercells (small cell cancers) in vitro. Studies in animals have confirmedthese findings, showing that exposure of macrophages to marijuanasmoke in vitro impairs their function, and that exposure of rats to marijuanasmoke in vivo makes them less able to inactivate bacteria (Staphylococcusaureus) delivered by aerosol to the lungs. The animal studiesalso indicated that the toxic effects of marijuana smoke on the immunedefenses were not due to THC but to some other components of themarijuana smoke, since smoke from THC-extracted herbal material remainedtoxic. These findings suggest that like tobacco smokers, marijuanasmokers are likely to be more susceptible to respiratory tract infectionsand possibly less able to defend against the development of lungcancers. An added complication is that some batches of herbal cannabismay be contaminated with fungi (e.g., Aspergillus species) that couldthemselves cause lung infections. This could be a particular hazard toAIDS patients whose immune defenses are already compromised.A similar concern is the contamination of some United States suppliesof herbal cannabis by the herbicide paraquat, used by the UnitedStates government to destroy cannabis crops in the United States and