TABLE 3.

Three potential pathways by which gut microbes may influence IDD.

Pathways	Mechanism of action
Bacteria Infiltration	Bacterial translocation across the gut epithelial barrier and into the IVD, when the intestinal barrier is adversely affected.
Immunomodulation	Dysbiosis of intestinal flora, bacterial contact with the mucosal immune system, promotes activation of the immune system and the release of large amounts of pro-inflammatory factors, which can accumulate toward and affect IVD.
Metabolites and Cytokines	Intestinal bacteria affect the absorption of nutrients by the intestinal epithelium and produce metabolites and cytokines that diffuse into and affect the IVD.

IVD, intervertebral disk degeneration; IDD, intervertebral disk degeneration.