Previously, we demonstrated that Lactobacillus jensenii TL2937 attenuates the inflammatory response triggered by activation of Toll-like receptor 4 (TLR-4) in porcine intestinal epithelial cells. In view of the critical importance of antigen-presenting cell (APC) polarization in immunoregulation, the objective of the present study was to examine the effect of strain TL2937 on the activation patterns of APCs from swine Peyer's patches (PPs). We demonstrated that direct exposure of porcine APCs to L. jensenii in the absence of inflammatory signals increased expression of interleukin-10 (IL-10) and transforming growth factor β in CD172a+ APCs and caused them to display tolerogenic properties. In addition, pretreatment of CD172a+ APCs with L. jensenii resulted in differential modulation of the production of pro- and anti-inflammatory cytokines in response to TLR4 activation. The immunomodulatory effect of strain TL2937 was not related to a downregulation of TLR4 but was related to an upregulation of the expression of three negative regulators of TLRs: single immunoglobulin IL-1-related receptor (SIGIRR), A20, and interleukin-1 receptor-associated kinase M (IRAK-M). Our results also indicated that TLR2 has an important role in the anti-inflammatory activity of L. jensenii TL2937, since anti-TLR2 antibodies blocked the upregulation of SIGIRR and IRAK-M in CD172a+ APCs and the production of IL-10 in response to TLR4 activation. We performed, for the first time, a precise functional characterization of porcine APCs from PPs, and we demonstrated that CD172a+ cells were tolerogenic. Our findings demonstrate that adherent cells and isolated CD172a+ cells harvested from swine PPs were useful for in vitro study of the inflammatory responses in the porcine gut and the immunomodulatory effects of immunobiotic microorganisms.

Background

Some studies have shown that probiotics, including Lactobacillus rhamnosus CRL1505, had the potential to beneficially modulate the outcome of certain bacterial and viral respiratory infections. However, these studies did not determine the mechanism(s) by which probiotics contribute to host defense against respiratory viruses.

Results

In this work we demonstrated that orally administered Lactobacillus rhamnosus CRL1505 (Lr1505) was able to increase the levels of IFN-γ, IL-10 and IL-6 in the respiratory tract and the number of lung CD3+CD4+IFN-γ+ T cells. To mimic the pro-inflammatory and physiopathological consecuences of RNA viral infections in the lung, we used an experimental model of lung inflammation based on the administration of the artificial viral pathogen-associated molecular pattern poly(I:C). Nasal administration of poly(I:C) to mice induced a marked impairment of lung function that was accompanied by the production of pro-inflammatory mediators and inflammatory cell recruitment into the airways. The preventive administration of Lr1505 reduced lung injuries and the production of TNF-α, IL-6, IL-8 and MCP-1 in the respiratory tract after the challenge with poly(I:C). Moreover, Lr1505 induced a significant increase in lung and serum IL-10. We also observed that Lr1505 was able to increase respiratory IFN-γ levels and the number of lung CD3+CD4+IFN-γ+ T cells after poly(I:C) challenge. Moreover, higher numbers of both CD103+ and CD11bhigh dendritic cells and increased expression of MHC-II, IL-12 and IFN-γ in these cell populations were found in lungs of Lr1505-treated mice. Therefore, Lr1505 treatment would beneficially regulate the balance between pro-inflammatory mediators and IL-10, allowing an effective inflammatory response against infection and avoiding tissue damage.

Conclusions

Results showed that Lr1505 would induce a mobilization of cells from intestine and changes in cytokine profile that would be able to beneficially modulate the respiratory mucosal immunity. Although deeper studies are needed using challenges with respiratory viruses, the results in this study suggest that Lr1505, a potent inducer of antiviral cytokines, may be useful as a prophylactic agent to control respiratory virus infection.