The effect of Lactobacillus rhamnosus CRL1505 (Lr) on macrophages (Ma) and dendritic cells (DC) in the orchestration of anti-pneumococcal immunity was studied using malnutrition and pneumococcal infection mouse models. Monocytes (Mo), Ma, and DC in two groups of malnourished mice fed with balanced diet (BCD) were studied through flow cytometry; one group was nasally administered with Lr (BCD+Lr group), and the other group was not (BCD group). Well-nourished (WNC) and malnourished (MNC) mice were used as controls.Malnutrition affected the number of respiratory and splenic mononuclear phagocytes. The BCD+Lr treatment, unlike BCD, was able to increase and normalize lung Mo and Ma. The BCD+Lr mice were also able to upregulate the expression of the activation marker MHC II in lung DC and to improve this population showing a more significant effect on CD11b+ DC subpopulation. At post-infection, lung Mo values were higher in BCD+Lr mice than in BCD mice and similar to those obtained in WNC group. Although both repletion treatments showed similar values of lung Ma post-infection, the Ma activation state in BCD+Lr mice was higher than that in BCD mice. Furthermore, BCD+Lr treatment was able to normalize the number and activation of splenic Ma and DC after the challenge.Lr administration stimulates respiratory and systemic mononuclear phagocytes. Stimulation of Ma and DC populations would increase the microbicide activity and improve the adaptive immunity through its antigen-presenting capacity. Thus, Lr contributes to improved outcomes of pneumococcal infection in immunocompromised hosts.
Keywords: Dendritic cells; Immunocompromised hosts; Lactobacillus; Macrophages; Pneumococcal infection.