TNF and Alzheimer disease: Pro-inflammatory GM can contribute to the activation of innate immune cells such as macrophages and microglia thus resulting in the release of proinflammatory cytokines, such as interleukin-1 beta (IL-1β) and tumor necrosis factor-alpha (TNF-α), which leads to increased permeability of gastrointestinal tract and potentially exacerbates neuroinflammation in AD [37].