Abstract
Summary
Evidence is presented to show that protective antigen undergoes subtle alterations that affect its biological activity. For one hour following intravenous injection of protective antigen (PA) into the rat, subsequent inoculation of lethal factor leads to death of the rat as expected. Two hours after injection of protective antigen, injection of lethal factor does not kill the rat although challenge with whole toxin produces the classical lethal response. At this time, PA is no longer demonstrable in the bloodstream by immunological methods. In contrast, 4 hours following an injection of protective antigen, rats not only do not die when injected with lethal factor but also are protected from the lethal effect of whole toxin. Some preparations of protective antigen can detoxify in vitro whole toxin of known potency. These facts are discussed in relation to the clearance from the bloodstream of injected whole toxin or its components and a possible role for PA in anthrax therapy is suggested.
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