Direct and indirect promotion of myelopoiesis mechanisms by postbiotics obtained from Lactobacillus rhamnosus CRL1505

Abstract

Many attempts have been made to find safer immunomodulatory agents that enhance the immune response and reduce the number and severity of infections in at-risk populations. Our previous studies have shown that Lactobacillus rhamnosus CRL1505 (Lr05) and its postbiotics, peptidoglycan (PG05) and cell wall (CW05), were able to improve bone marrow (BM) myelopiesis and to protect against respiratory pathogens in mice undergoing chemotherapy. However, the underlying mechanisms remain unknown. Hence, the role of TLR2 and G-CSF involved in the ability of Lr05, P05 and CW05 to induce basal myelopoiesis by direct or indirect interaction with BM hematopoietic stem and progenitor cells (HSPC) was evaluated. First, in vitro colony-forming unit assays were performed to assess whether the clonogenic capacity of BM cells responds to direct interaction with Lr05 and its postbiotics. For this, mouse BM cells were plated in the presence or absence of Lr05, PG05 or CW05 in culture medium for the granulocyte/macrophage forming unit (CFU-GM) (MethoCult? GFM3534). The counts and the phenotypic characterization of the colonies obtained were determined. Besides, the effect of the addition of fibroblast supernatants conditioned by Lr05 or its postbiotics on the clonogenic activity of HSPC was investigated. Finally, the expression of TLR2 of CFU-GM and the levels of G-CSF in the culture medium on day 14 were determined by flow cytometry and ELISA, respectively. Lr05 significantly stimulated the TLR2 expression and secretion of G-CSF, and enhanced the clonogenic activity of HSPC and fibroblast. Interestingly, CW05 showed a strong stimulatory effect while PG05 showed immune effects that were more similar to Lr05. These results allow us to know, at least in part, the cellular and molecular mechanisms involved in the myelopoiesis-enhancing capacity of new safe products to be potentially used in patients undergoing chemotherapeutic treatment.