Tu1978 Bifidobacterium Infantis 35624 Administration and Peyer's Patch Immune Response Following Salmonella Infection: The Role of Regulatory T-Cells and Chemokine Secretion

Background: The outcome following infection depends on the generation of an immune response that results in control of the pathogenic microorganism, while limiting the damage sustained to the host itself. In this regard, regulatory T cells (Treg) have been shown to play a pivotal role. Probiotics, such as Bifidobacterium infantis 35624, have been shown to be protective against Salmonella associated host injury in a mechanism involving induction and/ or recruitment of Tregs within the gastrointestinal tract. Aim(s): To examine the molecular mechanisms by which B. infantis-induced Tregs protect against Salmonella-associated infection and inflammation. Method(s): B. infantis 35624 was administered to animals for 6 weeks. Mice were subsequently inoculated with Salmonella orally and sacrificed after infection for 4 days. Peyer's patches single-cell suspensions were stimulated with anti-CD3/anti-CD28 for 48 hours and supernatants analysed for MIP-1 alpha, MIP-1beta, and RANTES. CD4+CD25- and CD4+CD25+ T cells were isolated from splenocytes using immunomagnetic beads and co-incubated with increasing numbers of splenocytes. Co-cultures were stimulated with anti- CD3/anti-CD28 antibodies for 48 hours and levels of cytokines and chemokines measured. Result(s): B. infantis 35624 feeding to Salmonella-infected mice has a significant impact on Peyer's patch chemokine secretion, where there was significantly reduced secretion of both MIP-1alpha and MIP-1beta. In addition, chemokine secretion was significantly inversely correlated with Peyer's patch CD4+CD25+ cell numbers. In vitro, CD4+CD25+ T cells inhibited TNF- alpha and IFN-gamma secretion, while CD4+CD25- T cells enhanced TNF- alpha and IFN-gamma production confirming that the balance between CD25+ and CD25- T cells influences pro-inflammatory cytokine release. However, both CD25+ and CD25- T cells suppressed MIP-1 alpha and MIP- 1beta secretion to the same extent in vitro. Conclusion(s): This data extends previous studies whereby B. infantis 35624-induced Tregs correlate with inhibition of chemokine secretion within the mucosa of pathogen infected animals. In addition, direct and indirect mechanisms may play a role as chemokine secretion is suppressed by both CD25+ and CD25- cells in vitro.