THE ADJUVANT EFFECT OF MICROBIAL PRODUCTS ON THE IMMUNE RESPONSE

Abstract

The commonly recognized adjuvants are remarkable for their diversity. This review is not intended to cover comprehensively the available list of adjuvants of microbial origin; rather, an attempt is made to evaluate some of the mechanisms which account for the activity of those microbial agents that have been subject in recent years to most investigation. The intention is to stress the common principles of adjuvant activity where these can be seen and to examine some of the experimental approaches. First, we should clarify the range of effects which experimenters in this field include under the term adjuvant. The systems currently used to study adjuvant action only rarely measure induced immunity-for example, the development of increased powers of resistance to a challenge by living microbial agents or virus­ although much recent investigation has been devoted to adjuvants for increasing tumor immunity, that is, nonspecific substances which can be injected before or during the induction of neoplasia and result in increased survival of the host. Both mycobacteria and various anaerobic coryneform bacilli have been used extensively in humans and experimental animals with this intention. The effects observed could depend upon increased nonspecific or specific immune mechanisms. Thus a non­ specific increase of the phagocytic powers of macrophages could possibly explain many ofthe favorable experimental results in tumor immunity without invoking any influence en. specific adaptive immunity. Alternatively