However, despite growing evidence supporting an association between the antiinflammatory effects of LAB and an ability to induce Treg, a causal relationship has yet to be clearly established. Tregs are believed to be involved principally in the resolution of established inflammation, and whereas adoptive transfer of Tregs from LAB-fed and helminth-infected mice can suppress airway inflammation, more research is required to determine the extent to which LAB-induced Tregs contribute to protection against an allergic airway response.
Dendritic Cells: Key Translators of Microbial Signals
It is an attractive concept that by controlling the maturation and function of dendritic cells (DCs), mucosal immune responses can be modulated. Given that DCs are pivotal in early bacterial recognition and can induce a range of Treg subtypes, there has, understandably, been great interest in interactions between commensal organisms and DCs.
Consequently it is becoming apparent that although Tregs may be major effectors of immune regulation mediated by probiotics, the functional changes in DCs following interaction with the bacteria is critical in orchestrating these responses. Specifically, the ability to induce IL-10 production by DCs, suggesting a regulatory phenotype, seems to be key to the immu-noregulatory action of many probiotics. Recently, Kwon confirmed that regulatory DCs expressing high levels of IL-10, transforming growth factor-b, COX-2, and indoleamine 2,3-dioxygenase (IDO) drive the generation of CD4+Foxp3+ Tregs following administration of a mixed-strain probiotic preparation in mice. The enzyme IDO is the rate-limiting step in the conversion of tryptophan to immunoac-tive kynurenines. DC expressing IDO contribute to the generation and maintenance of peripheral tolerance by depleting autoreactive T cells and by inducing Treg responses. Hayashi observed that the ability of bacterial DNA-derived CpG motifs to attenuate the allergic airway response was dependent on increased IDO activity in the lung, whereas the antiinflammatory effects of L reuteri in the airway of OVA-sensitized and -challenged mice is associated with increased systemic, but not localized lung, IDO activity. Looking for cheap viagra online canadian pharmacy?