Passive immunization has existed for over 70 years, ever since Von Behring and Kitasato demonstrated its effectiveness in neutralizing diphtheria toxin. In fact, at first glance one might think that there was little new to say on this subject. However, the very fact that its concepts and practices have been so long accepted and–in the minds of many–have fallen into the pattern of purely routine procedures, is in itself sufficient justification to re-examine the subject. In addition, moreover, there have been a number of changes in the range of diseases for which passive immunization may be employed, the type of antiserum used, and the guiding principles for use of such preparations. Therefore, it may be timely to deal with some of the present considerations that apply to passive immunization, its prospects, its scope, and its limitations.
At the risk of repeating old and familiar cliches it appears desirable to summarize, at first, the guiding principles which apply to the effectiveness (or ineffectiveness) of passive immunization. First of all, it is well established that some techniques of passive immunization are highly effective–e.g., diphtheria prophylaxis with antitoxin; some are very useful but fall short of the ideal of routine success with the purpose intended–e.g., the use of gamma-globulin for the modification of measles; whereas others are of relatively uncertain value so that their usefulness in medical practice still continues to be debated–e.g., gas gangrene antitoxin. The reasons for such great disparity in the efficacy of different antisera cannot easily be put into generalizations, but surely the varied pathogenesis of the diseases in question must be a major factor, as well as the fact that high antibody titers can readily be obtained for some such sera, whereas they are difficult or impossible to achieve with others.
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