Abstract
Enhancement of host resistance to infectious agents is a major objective of preventive medicine. One area of investigation of this objective is the influence of genetics on specific immunological host responses (1-10). For instance the amount of antigen needed to induce antibody synthesis (3) and the types of antibody produced (5, 7, 8, 10) are under genetic control. Hence an important factor in the evaluation of vaccine potency is not only the species but also the strain of animal used in the tests. Another area of investigation explores ways to induce a nonspecific enhancement of the immunological response (11-21). A wide variety of substances have been used both as adjuvants, to increase specific humoral responses, and as general reticuloendo-thelium stimulants. For instance: Vitamin E as a supplement in diets has been shown to increase the IgG produced in response to tetanus toxoid (11). Bordetella pertussis vaccine and beryllium sulfate have been shown to be potent adjuvants for increasing antibody response via their effect on macrophages (13). Hyperphagocytic activity of the reticuloendothelial system by glucan increased the primary and secondary immune responses of mice (15). Zymosan (17-20) and bacterial endotoxins share certain chemical and biological properties and both have been used to increase phagocytosis and humoral responses to many different infections. However, zymosan does not have the toxic properties of endotoxin and hence its use in the studies of nonspecific host resistance is less complicated. Methanol extract of the tubercle bacilli (24, 25) (referred to as MER) has the interesting property of prophylactically protecting not only against the tubercle bacilli, from which it is derived, but against such widely different bacterial infections as those caused by staphylococci and Klebsiella. Moreover, mice are protected for as long as 12 weeks after injection with MER.
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