Fecal microbiota transplantation in allergic diseases

Table 1 Potential roles of probiotics and fecal microbiota transplantation in alleviating or preventing allergic diseases[99]

Probiotics and FMT	Potential roles
Probiotics	Epithelial integrity ↑
	Tight junction protein expression ↑
	Bacterial translocation ↓
	Inflammatory cytokines such as IL-6, IL-8 and TNF-α ↓
	Restoration of Th1/Th2 balance
	Treg cell numbers and function, IL-10 and TGF-β ↑
	SCFAs production (especially butyrate) ↑
FMT	Pro-inflammatory cytokine secretion ↓
	Restoration of Th1/Th2 balance
	Stimulates T cell activity and leukocyte adhesion
	Change in intestinal bacterial diversity (Firmicutes, Bacteroidetes ↑/Proteobacteria, Actinobacteria ↓)
	Intestinal permeability ↓
	Epithelial integrity ↑
	SCFAs production ↑
	Intestinal pH ↓
	Bacterial adhesion to H2O2 ↑

SCFA: Short chain fatty acid; FMT: Fecal microbiota transplantation; TNF-α: Tumor necrosis factor-alpha; IFN-γ: Interferon-gamma; IL: Interleukin.

Table 2 Impact of fecal microbiota transplantation on allergic diseases

Disease	Species	Main result	Ref.
Food allergy	Mice	Food allergy protection was achieved in food allergy-prone recipient mice receiving FMT from a healthy donor	[69]
	Mice	It has been shown that recipient germ-free mice after FMT from healthy and cow's milk allergy-free donors are protected against anaphylactic reactions to cow's milk allergen	[70]
	Human	Phase 1 and phase 2 study investigating the efficacy of oral capsule FMT in people with peanut allergy is ongoing	[71,72]
Eosinophilic gastritis	Human	Combination of FMT and steroid therapy in a patient with steroid-resistant eosinophilic gastritis improved the patient's symptoms	[76]
Allergic proctocolitis (FPIAP)	Human	After 2 days after administration of FMT via rectal tube to 19 infants with FPIAP, 17 infants showed symptomatic regression	[80]
Atopic dermatitis	Mice	In recipient mice after FMT administered from non-atopic dermatitis patients to atopic dermatitis patients: SCFA ↑, Th1 cytokines (IL-12, IFN-γ, TNF-α) ↑, Th2 cytokines (IL-4, IL-5, IL-13) ↓, Total IgE ↓, SCORAD ↓	[86,87]
	Human	After FMT in patients with moderate to severe AD: SCORAD ↓, need for topical corticosteroids ↓	[88]
Allergic rhinitis	Mice	In recipient mice after FMT: nasal symptoms ↓, Total IgE ↓, histopathological recovery (decrease in eosinophilia)	[91]

SCFA: Short chain fatty acid; FMT: Fecal microbiota transplantation; FPIAP: Food protein-induced allergic proctocolitis; SCORAD: Scoring atopic dermatitis; TNF-α: Tumor necrosis factor-alpha; IFN-γ: Interferon-gamma; IL: Interleukin.