Oral administration of milk fermented by Lactobacillus casei CRL431 was able to decrease metastasis from breast cancer in a murine model by modulating immune response locally in the lungs.

Graphical abstract Highlights • Milk fermented by L. casei CRL431 (PFM) diminished lung metastasis in a mouse model. • PFM modulated the immune response to fight against tumour cells in the lungs. • Systemically, PFM administration modulated the inflammatory response. • Decreases of IL-10+ F4/80+ cells in lungs were associated to PFM beneficial effect. Abstract The host immune system is an important factor to combat metastasis. In this work, it was evaluated the immunomodulation exerted by milk fermented with the probiotic strain Lactobacillus casei CRL431 (PFM) when was administered to mice in the metastatic stage of breast cancer. Mice received PFM were compared to animals given milk. PFM administration diminished metastasis in the lungs and increased the survival of the animals. Systemically, PFM administration decreased pro-inflammatory cytokines and locally in the lungs (metastatic organs) decreased F4/80+ cells, principally IL-10/F4/80+ cells. The highest percentages for CD4+ and CD4+CD8+ cells were observed in PFM group. Finally, immune cells from lungs of mice given PFM showed lower production of most cytokines evaluated when they were re-stimulated in vitro with tumour cells. The results obtained suggest that modulation of immune cells in the lungs by PFM could be a strategy to fight against tumour cells in the metastatic sites. [ABSTRACT FROM AUTHOR]