Indeed, CD4+CD25+ transferred from L reuteri-fed nonsensitized mice can attenuate the allergic airway response in ovalbumin (OVA)-sensitized animals. L rhamnosus GG has also been shown to reduce the murine allergic airway response, with associated increases in Foxp3+ T cells, but only when the bacteria are administered in the neonatal period. This led to the suggestion that probiotic intervention might be successful primarily in the initial stage of intestinal colonization, a time point that is believed to be crucial for the maturation and balance of the immune system Viagra online. However, as described previously, it is clear that certain strains of LAB can have profound immunoregulatory and antiallergic effects when administered to adult mice.
Interestingly, Lyons demonstrated that one particular strain of Bifidobacterium induced Tregs only when fed to mice in the perinatal period, whereas another strain was able to induce Tregs in both adult and neonatal mice. Only this second strain attenuated the allergic airway response in adult OVA-sensitized mice. This suggests that a combination of bacterial strain-specific characteristics and host-specific processes, such as immunologic maturity, mucosal lymphoid antigen sampling, and gut barrier integrity, may be important for the induction of host regulatory responses.
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LAB can induce a regulatory response that does not require prior exposure of Tregs to a specific allergen. Once activated, Tregs can suppress effector T cells in an antigen-nonspecific way called “bystander suppression,” and in vivo transfer studies demonstrate that Tregs can create a regulatory milieu that promotes the outgrowth of new populations of Tregs with antigen specificities distinct from those of the original population. In this way, certain LAB may induce Tregs in the gut-associated lymphoid tissue (GALT) that can spread to the airways in response to immune challenge and inflammation (Fig 1). This is supported by the finding that oral treatment with L reuteri results in an increase in Tregs in the draining lymph nodes of the lung, relative to vehicle-treated control subjects, only following airway challenge in sensitized mice.