Biological effects of microorganisms and their substances in mice

In our experiments we evidence from several aspects that the normal microbial flora has a permanent and life-long immune modulating role in conventional organisms and a stimulating effect both on specific and non-specific defense. However, in case of artificial interventions (stress, drugs) affecting the organism, existence of the normal flora may have an adverse effect on it (endotoxin effect, bacterial translocation). The immunomodulants show a stimulating effect mainly in organisms with undeveloped immune system, and their effects are independent from the presence or absence of the microbial flora. With ageing, effect of immunomodulants can change and become indifferent or even suppressive. Dose-dependence of stimulating or suppressing effect of immunomodulants may be related to their non-immunological effects (endotoxin effect, bacterial translocation). Finally, on the basis of our experiments, we consider the Gf mouse suitable for examining the effect of a given agent in the practice, on the one hand, and for observing the host organism's reactions, free from the influence of the normal microbial flora, on the other. Along with the known physiological and pathological events, our results draw also attention to as distant fields as drug sensitivity, drug interactions influencing drug sensitivity. The authors put emphasis on importance of germfree environment during immunosuppressive treatments in humans and when making special examinations under experimental conditions.