Beneficial effects of fermented milks
The fermented milk is a dairy product made with milk or concentrated powder that has suffered pasteurization, sterilization or boiling, which was inoculated LAB belonging to one or several species, features for each product. The LAB are characterized during fermentation transform some sugars, especially lactose, organic acids (lactic and acetic). They are used to produce yoghurt and certain products of fermentation of milk.
Studies conducted in animals and humans have focused on the effects of fermented milks on three priority functions of the immune system: antigen recognition, regulation and destruction of the material destroyed. Thus, it has become apparent that macrophages, specific immunoglobulins and some cytokines are modified after ingestion of fermented milk.
It was also suggested that regular intake of fermented milk products may be beneficial for preventing common infectious diseases by ingestion of pathogens. In this sense, it was found that childhood diarrhea improved significantly after the ingestion of fermented milk products, which has been attributed to its immunomodulatory effect probably exerted at the level of the intestinal mucosa. One researcher found longer survival periods in mice who ate fermented milk with 8 types of LAB for 13 days before inducing a process of infection after inoculation with Klebsiella pneumoniae is believed that this result involves high levels of IgG produced by the LAB.
Phagocytosis
Phagocytosis is a mechanism called non-specific immune response. This mechanism is activated by certain molecules that act as signals, several authors have demonstrated the activation of this function when given milk fermented with lactobacilli. An increase in the phagocytic capacity, in 28 human volunteers after consuming 7 x 10 10 cfu / day of B. bifidum or L. acidophilus contained in 360 ml of fermented milk. This effect has been observed immediately after the conclusion of 3 weeks of eating the fermented product. Curiously, however, phagocytic activity is further increased when measured 6 weeks after stopping the intake of fermented milk.
Humoral Immunity
In a group of elders after consuming B. bifidum and L. acidophilus. An increase of B cells in peripheral blood with a reduction in colonic inflammation Yasui and Ohwaki have shown that stimulation of proliferation of B lymphocytes in Peyer's patches can be induced by Bifidobacterium shortly.
The consumption of yogurt or fermented with L. acidophilus, Bifidobacterium longum and mixtures of different LAB led to a significant increase in various immune parameters, such as cells that produce secretory immunoglobulin A, IgG levels and specific antibody response.
When implementing a vaccination therapy with oral administration of Lactobacillus casei, in children between 2 and 5 months of age has been shown the immuno-stimulatory effect of the vaccine against rotavirus, resulting in an increase of IgM-secreting cells specific for the infectious agent cited. In a similar study of vaccination against S. typhimurium and previous intake of milk fermented with L acidophilus and Bifidobacterium have been found increased total and specific IgA.
It has been demonstrated in human volunteers that the ingestion of milk fermented with L. acidophilus (5x109 cfu), consecutive to oral vaccination with an attenuated strain of Salmonella typhi significantly increased serum levels of immunoglobulin A against the pathogen lipopolysaccharide.
Cellular Immunity
Schiffrin and coworkers observed no changes in lymphocyte subpopulations of adults after ingestion of B. bifidum or L. acidophilus. Other researchers reported increases in T cell population in general.
Cytokines
In studies in vitro has been observed that by incubating peripheral blood mononuclear cells with L. casei, L. acidophilus or Bifidobacterium sp increases the production of IL1-a, TNF-a and IFN-g. Both intestinal bacteria such as lactic induce the secretion of cytokines, so it might be a link between certain foods, intestinal flora and immune system regulation.
The L. acidophilus Ke-10 also has an immunomodulatory effect in experiments both in-vivo and in vitro. Thus, it has proven its ability to restore the proliferative activity of lymphocytes to produce IL2 in rats with radiation-induced immunodeficiency.
It has also been observed that L. acidophilus, both active and strains in sterilized product induces IFN-g production by macrophages.
Other researchers have found that, after trying various lactic acid bacteria, Lactobacillus helveticus in only half of which protein source is the b-casein, is capable of modulating lymphocyte proliferation, but does not exercise any action on the cytotoxic activity of cells natural killer. When the culture supernatant is activated by mitogen canavalin A is an increase in the production of IFN g and decreased levels of IL-2, results that correlate with decreased lymphocyte proliferation. The authors conclude that activity in the culture supernatant could be related to the interaction with monocytes-macrophages and T cells "help", especially the Th1 type0.
To study the mechanisms of action resulting from the fermentation of milk with lactic acid bacteria, have conducted several studies to investigate which components from LAB could be involved in the development of immunomodulatory activity.
In this sense, the production has been attributed to the effect of cytokines could have a component of the cell wall of lactic acid bacteria.
For its part, it has been determined that the production of pro-inflammatory cytokines (IL1-a and TNF-a) from macrophages by a particular strain of L. acidophilus (LA1) depends on a component of nature from the LA1 lipopolysaccharide, as the LPS of E. coli at different concentrations fails to stimulate the secretion of these cytokines. A study to determine to what extent the yogurt conducive to recovery in a group of anorexics, we measured the synthesis of interferon g (INF-g), interleukins 2, 4, and 6 and tumor necrosis factor (TNF). The results showed a significant increase of these cytokines in the period in which patients took the yogurt.
In a recent and innovative research project carried out in vitro compared the immunological effects of LAB and Enterobacteriaceae on various human enterocytes. While the Enterobacteriaceae are able to activate intestinal epithelial cells themselves, the LAB do so by inducing the expression of certain surface markers in intestinal epithelial cells making them more sensitive to the simultaneous exposure of IFN-g. Moreover, the mechanism triggered by the enterobacteria leads to a local inflammatory response (with production of IL-8, MCP-1, TNF-a and GM-CSF) is not the case with the LAB, feature in conjunction with protective role of the intestinal mucosa.
Allergies
It is a condition in which one begins to study the effects of LAB, however, so far, the results are controversial and do not know the mechanisms of action.
It has been observed remission rate of nasal allergy symptoms in a population of 42 young and 56 adults, after ingestion of 200 grams per day of yogurt for 1 year, compared with a control group. However, there are unknown mechanisms might be involved, since the authors have found no significant differences in immune parameters studied.
In another study, with design of a cross-over, in which individuals with asthma are subject to an intake of 225g of yogurt 2 times a day with or without L. acidophilus for 1 month, has been found in the group consuming yogurt with L. acidophilus that IFN-g levels are higher and eosinophilia is less. However, there are significant differences in clinic patients or in their quality of life.
Similarly, when studied in atopic patients the effects of yogurt containing Lactobacillus bulgaricus and Streptococcus thermophilus, there has been no significant improvement in immune parameters studied (phagocytic function and humoral and cellular immune responses.
Diarrhea
It was considered that the concept of probiotics for acute and chronic diarrhea is very important, demonstrating that some are very effective, providing cost-benefit advantages in treatment.
It was observed that when ingested fermented milk with L. casei and L. acidophilus for 8 days before inoculation with Shigella sonnei is an increase in the survival of experimental animals and an increased serum antibodies against the bacteria, suggesting protection against intestinal infectious process.
The effect of Bifidobacterium in its passage through the gut and the mechanisms by which stimulate the immune system have been studied, being able to check that the regular consumption of fermented milk can prevent infection through the action of secretory IgA that prevents absorption antigen by the mucosal epithelium and its entry into the body and thus prevents the attachment of pathogenic microbes to the intestinal epithelium.
Rotavirus is extremely contagious and attacking young children, infecting the cells of the colon and causing very strong diarrhea each year are responsible for the deaths of some 90 000 children worldwide.
The death rate from diarrhea in malnourished children is greater than 1% and it was found that probiotics can prevent colonization by certain bacteria and viruses that cause diarrhea.
In a study of 39 children between 7-39 months with acute rotavirus gastroenteritis was observed that intake of L. casei increased levels of cells secreting IgA, IgG and IgM, also decreasing the duration of diarrhea compared with a control group (1.1 days in the group with L. casei vs. 2.5 days in group with placebo).
Cancer
Although still not been able to verify the exact mechanism of antitumor action of probiotics is hypothesized increased apoptosis or programmed cell death of cells in the intestine compared to a carcinogen.
Some doctors described the hypothetical pathways by which probiotic bacteria induce their effect on reactions that have a role in the early stages of colon carcinogenesis and the effect of fecal enzymes on the metabolism of carcinogenic substances in Inside the gut, the ability of probiotic bacteria to prevent the absorption of mutagens and carcinogens in the intestine, and the effects of probiotics on the kinetics of colonic epithelial cells.
It was shown that in 48 patients with bladder cancer, which after eating L. casei for one year, after having undergone resection of the tumor, the interval of time that elapsed before the reappearance of that was longer than in the control group who ingested a placebo, 350 days versus 195 days of the study group.
Have also conducted studies in mice to observe the prevention and treatment of cancer found a significant decrease in the development of secondary tumors when animals were previously fed with L. casei observed that consumption of L. casei inhibited the growth of a fibrosarcoma implanted subcutaneously, these authors emphasized the importance of concentration and frequency of ingestion of L. casei in the development of these effects.
The effect of yogurt carcinogenic compounds against different experimental colon level. To determine whether the antimutagenic activity requires the presence of bacterial growth, the results were compared against those obtained with non-treated fermented milk or lactic acid. Milk extracts showed the same low antimutagenic activity, approximately 2.5 times lower than that found in yogurt extract, thus demonstrating the importance of the presence of LAB.
A group of doctors conducted a study in mice fed with yogurt, which he induced an intestinal tumor, the animal fed yogurt remained, resulting in an inhibition of intestinal carcinoma, com-producing cells increased IgA and T lymphocytes.
In studying the effect of milk fermented with various strains of LAB (Bifidobacterium infantis, Bifidobacterium bifidum, Bifidobacterium animalis, Lactobacillus acidophilus and Lactobacillus paracasein) on the growth of a cell line of breast cancer, has shown inhibition of the same, being the most effective strains Bifidobacterium infantis and Lactobacillus acidophilus. Noteworthy is the fact that there can relate to the antiproliferative effect of the presence of bacteria in fermented milk or whole milk or one of its main fractions (lactalbumin or beta-lactoglobulin), since they are unable to affect the cell growth. Therefore, it suggests the presence of a soluble compound produced ex novo by LAB during fermentation of milk, which has antiproliferative activity and is useful in the prevention and therapy of serious tumors, including breast cancer.
Recent results have described the scientific basis by which yogurt exerts its antitumor effect, suggesting it could be: the decline of the inflammatory response through the increase of IgA + cells, avoiding the formation of oxidant radicals, which are mutagenic and favor tumor development and / or decrease in mitotic index and increased apoptosis, by releasing cytokines.
Conclusion
Because fermented milks have a modulating effect on the intestinal mucosa, could exert a preventive mechanism against infectious diseases and a persistence of immune system homeostasis without inducing adverse effects such as allergies or autoimmune reactions.
Study needs more research in both basic and experimentation in the practical application, to understand various issues still unresolved. For example, the nature of the interaction of fermented milks at the intestinal mucosa and the mechanisms involved. It will also be important to establish the relationship between immune response and the observed beneficial effects on health. The next step is identifying those LAB (species, strains) most beneficial for different purposes, and to determine the concentration and frequency of consumption of various forms of fermented milk products, for optimum effects, and the development of new products with specific positive effects for a particular purpose.
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