The Mucus Binding Factor Is Not Necessary for Lacticaseibacillus rhamnosus CRL1505 to Exert Its Immunomodulatory Activities in Local and Distal Mucosal Sites

Both viable and non-viable orally administered CRL1505 modulate immunity in local (intestine) and distal (respiratory) mucosal sites. So, intestinal adhesion and colonization are not necessary for this probiotic strain to exert its immunomodulatory effects. In this work, a mucus-binding factor knockout CRL1505 strain (Δ CRL1505) was obtained and the lack of binding ability to both intestinal epithelial cells and mucin was demonstrated in vitro. In addition, two sets of in vivo experiments in 6-week-old Balb/c mice were performed to evaluate Δ CRL1505 immunomodulatory activities. (A) Orally administered Δ CRL1505 prior to intraperitoneal injection of the Toll-like receptor 3 (TLR3) agonist poly(I:C) significantly reduced intraepithelial lymphocytes (CD3 NK1.1 CD8αα ) and pro-inflammatory mediators (TNF-α, IL-6 and IL-15) in the intestinal mucosa. (B) Orally administered Δ CRL1505 prior to nasal stimulation with poly(I:C) significantly decreased the levels of the biochemical markers of lung tissue damage. In addition, reduced recruitment of neutrophils and levels of pro-inflammatory mediators (TNF-α, IL-6 and IL-8) as well as increased IFN-β and IFN-γ in the respiratory mucosa were observed in Δ CRL1505-treated mice when compared to untreated control mice. The immunological changes induced by the Δ CRL1505 strain were not different from those observed for the wild-type CRL1505 strain. Although it is generally accepted that the expression of adhesion factors is necessary for immunobiotics to induce their beneficial effects, it was demonstrated here that the protein is not required for CRL1505 to exert its immunomodulatory activities in local and distal mucosal sites. These results are a step forward towards understanding the mechanisms involved in the immunomodulatory capabilities of CRL1505.