Nutritional supplementation, including probiotics, in this population may help maintain immune function either by direct interaction with the host immune system or indirectly by re-equilibrating the gut microbiota. The development of strategies aimed at counterbalancing the immune frailty in the elderly is a major challenge for 21 st century medicine. Moreover, it has been also shown that the age-dependent modifications of the composition of the gut microbiota also contribute to the defective local and systemic immune defenses in the elderly population. SIgA, the predominant immunoglobulin class in human external secretions, is a key element in the maintenance of gut microbiota homeostasis and in the protection of gastrointestinal and respiratory tracts against pathogens. In addition, the production of secretory IgA (SIgA) at the mucosal surfaces decreases with age and can lead to an increased risk of infection. A dramatic reduction in B cell repertoire associated with a decreased systemic antibody response to vaccination has been observed in the elderly population showing that the B cell compartment is also affected by ageing. Moreover, age-dependent thymic involution leads to the reduction of circulating naive T cells and the increase frequency of regulatory, memory and effector T cells. For innate dysfunction, it has been described that the function of natural killer cells, dendritic cells, macrophages and neutrophils decrease in the elderly. Ageing is associated with a decline of innate and adaptive immune responses. Viral respiratory and gastrointestinal infections are a predominant cause of morbidity and mortality in the elderly whose ageing immune system contributes significantly to poor outcomes. A post-hoc analysis on this subset showed a decreased frequency of respiratory infections in the probiotc group compared to the placebo group. subtilis CU1 significantly increased fecal and salivary secretory IgA concentrations compared to the placebo. However, in the subset of forty-four randomized subjects providing biological samples, we showed that consumption of B. subtilis CU1 supplementation did not statistically significantly decrease the mean number of days of reported CID symptoms over the 4-month of study (probiotic group: 5.1 (7.0) d, placebo group: 6.6 (7.3) d, P = 0.2015). Blood, saliva and stool samples were collected in a predefined subset of the first forty-four subjects enrolled in the study. Symptoms of gastrointestinal and upper/lower respiratory tract infections were recorded daily by the subjects throughout the study (4 months). This scheme was repeated 4 times during the study. subtilis CU1 spores daily) by short periodical courses of 10 days intermittently, alternating 18-day course of break. Subjects consumed either the placebo or the probiotic (2.10 9 B. One hundred subjects aged 60–74 were included in this randomized, double-blind, placebo-controlled, parallel-arms study.
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