CONICET | Buscador de Institutos y Recursos Humanos

In the twentieth century, scientist Ellie Metchnikoff suggested that the consumption of live microorganisms present in fermented products could explain the longevity of certain ethnic groups in Eastern Europe. He demonstrated that these aliments containing lactic acid bacteria (LAB) capable of producing lactic acid from the sugar of milk are substances that inhibit the growth of harmful microorganisms. His book The Prolongation of the Life published in 1907 confirmed the importance of the intestinal microbiota in protecting against disease. LAB and bifidobacteria are two populations of the intestinal microbiota that are associated with many beneficial effects for the host. Health can be affected by diet, antibacterial drugs, chemotherapy, stress, etc., and probiotic supplements can repair these defects. The word probiotic, relating to feed supplements, dates back to Parker in 1974; however, the history of live microbial feed supplements goes back hundreds of years, and the concept of fermented milk in many different forms has continued until the present day. The beneficial claims of probiotic supplementation are numerous and include improved growth rate, and utilization of food, milk, or egg production for farm animals (Lehloenya et al., 2008). For humans, they include resistance to infectious disease, cancer prevention, regulation of peristalsis and decrease in the symptoms of lactose deficiency, decrease in the gut inflammatory response, and prevention of food allergy (Aureli et al., 2011). In most of the effects attributed to probiotics, the immune system plays a key role, and as LAB are usually ingested as part of the normal daily diet in yoghurt, fermented milks, cheese, sausages, etc., the effect of these bacteria on the systemic and mucosal immune systems is extremely important, to establish the scientific basis for probiotic use and to determine how these nonpathogenic microorganisms influence the immune system. In this sense, experimental models in mice are useful. Even though all the results from animal models cannot be extrapolated to humans, the value of the studies conducted in experimental animal models is undeniable when attempting to understand the behavior of the probiotic or fermented milk containing these microorganisms in different pathologies where the immune system is involved. It has been shown that the substances that enhance or stimulate the immune response (adjuvant or immunomodulatory substances) can enhance the nonspecific defense mechanisms of the host and activate the cells involved in the innate and/or the adaptive immune response (Bomford, 1990; Cox and Coulter, 1997). Probiotics may activate the immune system by stimulating one, or all the types of response. If probiotics have the potential to exert an effect by preventing diseases where the immune system plays a pivotal role, the first question to answer is: Can these microorganisms act as adjuvants of the immune system? This question is prompted by the knowledge that the oral administration of antigen may induce or inhibit an immune response. Whether one effect occurs or another depends on various factors such as the nature of the antigen (soluble or particulate), where the dose of the antigen and the number of stimulations play an important role. Before a new substance can be used as an oral immunomodulator, its efficiency in the enhancement of the immune response and the absence of harmful effects for the host, such as intestinal inflammatory effect, disturbance in the microbiota (which could induce bacterial translocation), and the absence of any side effects on the intestinal ecosystem that might occur as the result of long-term administration, must be determined. The influence of the oral administration of probiotic bacteria or fermented milk containing these microorganisms or the bacteria-free fraction from fermented milk on the immune system has been studied in our laboratory.

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