New immunobiotics from highly proteolytic Lactobacillus delbrueckii strains: their impact on intestinal antiviral innate immune response

Proteolytic starter cultures with intrinsic immunomodulatory activities are desirably features for the development of functional foods, which would significantly reduce the cost of their production (one-strain starter) having an additional beneficial effect on the host. In this work, Lactobacillus delbrueckii strains were selected according to their ability to efficiently hydrolyse β-casein and to modulate the immune system. Among 36 strains evaluated, the highest proteolytic activities were found for L. delbrueckii subsp. lactis CRL581 and L. delbrueckii subsp. bulgaricus CRL656. The immunomodulatory effect of both strains and their β-casein hydrolysates (CRL581 and CRL656 hydrolysates, respectively) were studied in a murine model. Balb/c mice were fed lactobacilli or their hydrolysates for three days. One day after the last lactobacilli or hydrolysate treatments, mice were challenged with the Toll-like receptor 3 (TLR3) agonist poly(I:C) by intraperitoneal injection. Before and after poly(I:C) challenge the phagocytic and microbicidal activity of peritoneal macrophages, intestinal immunoglobulin A (IgA), cytokine profile, and histological analysis of the intestine were analysed. L. delbrueckii subsp. lactis CRL581 significantly increased the activation of peritoneal macrophages as well as the levels of intestinal IgA, interleukin (IL)-10 and interferon (IFN)-γ when compared to untreated controls. In addition, the CRL581 strain was able to significantly reduce the intestinal inflammatory damage triggered by TLR3 activation. L. delbrueckii CRL581 increased the levels of IL-10, IFN-γ and IFN-β, and reduced tumour necrosis factor alpha and IL-6 concentrations in the intestine of poly(I:C)-challenged mice. No immunomodulatory effects were observed for the CRL656 strain or for the CRL581 or CRL656 hydrolysates. The results of this work show that the technologically relevant and high proteolytic strain L. delbrueckii CRL581 is able to beneficially modulate the intestinal innate antiviral immune response. Although further studies with the CRL581 strain are required to corroborate and deepen its immunological effects, this bacterium is an interesting alternative for the development of new functional foods with antiviral capabilities.