Table 1 The gut microbiota-immuno-brain axis

Structural and maturation pattern [30, 31, 40]; reduce oxidative stress and mitochondrial dysfunction [41]

Microglia

Implicated in Parkinson’s [43], Huntington disease [44, 45], MS [46, 47]

Regulate levels [68]; promote recruitment and migration [71]; inhibit nitric oxide generation [72]; enhance effector responses [73,74,75]

Neutrophils

Implicated in stroke, Alzheimer’s, Parkinson’s, Huntington disease, MS, autism [76], epilepsy [77]

Regulate intestinal levels [69]; dampen degranulation and development food allergies [176]

Mast cells

Involved in neurogenesis, neuroinflammation, neurodegeneration, disruption of the BBB. Implicated in Alzheimer’s, Parkinson’s, Huntington disease, ALS [78]

Promote anti-inflammatory phenotype [29, 65]

Dendritic cells

Implicated in stroke, brain tumors, MS, Alzheimer’s, Parkinson’s, and epilepsy [82]

Promote anti-inflammatory phenotype, chemotaxis, and phagocytosis [29, 65]; affect polarization and reduce glycolysis [79, 80]

Macrophages

Implicated in neurodegenerative (i.e., Parkinson’s and Alzheimer’s) and neuroinflammatory disorders (MS and ALS) [81]

Promote differentiation of NKp46 + cells expressing RORγt [65], which regulate mucosal immunity [85]

NK

Reside in the meninges at steady state and migrate to the brain parenchymal during stroke and MS [85]

Modulate CD4 + Th differentiation (Th1, Th2, Th17 or Treg) [29, 65, 88, 91, 92]

Regulate CD8 + cell function [65, 95] and maintenance [96]. SCFAs enhance CD8 + T cells activation and differentiation into long-lived memory cells [98, 99]

T cells

CD4 + accumulation is associate with hemorrhagic brain injury pathology [93]

CD8 + are implicated in neurodegenerative conditions (i.e., Parkinson’s, Alzheimer’s, and MS) [100]; as well as in neuroinflammation, endotheliopathy [101], limbic encephalitis [102], and Rasmussen encephalitis [103]

Impact B cell anatomical clustering and function [104]. SCFAs can play contrasting roles on B cell epigenetics, class switching, antibody responses, and differentiation [107, 108]

B cells

Implicated in MS, neuromyelitis optica spectrum disorder, MOG antibody-associated disorder, Anti-N-methyl-D-aspartate receptor encephalitis, autoimmune epilepsy, Parkinson’s and Alzheimer’s disease [109]