Figure 3.

Immune cells along the gut-lung axis. Immune cells such as ILC2s, ILC3s and Th17 could transfer from the intestine to the lungs and participate in the inflammatory responses. The migration of immune cells is expedited by intestinal bacteria and their metabolites via IL-33 and IL-25; Intestinal bacteria could change the activity of T lymphocyte subsets through NF-κB and STING signaling pathways; L-selectin expressed by naive T cells binds to MAdCAM-1, exposing binding sites for α4β7 activation and ultimately altering the cytoskeleton; Pathogenic bacteria can be transferred to the lung through the gut-lung axis to trigger inflammatory responses, while probiotics could migrate to the lungs and reduce the inflammatory responses by the production of antibodies and enhancement of NK cells; Bifidobacterium enhances the inflammatory responses caused by the migration of pathogenic bacteria.