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Description
Effects of Glutathione on HIV and Th17 Depletion in GI Tract In the GI tract, Th17 cells maintain mucosal integrity by producing IL-17, which is a cytokine responsible for mobilizing neutrophils and myeloid cells and also for regeneration of epithelial cells via claudin induction [56]

So it's worth asking if their intake of B12 could be an influence
Kwak et al

10.1038/86882 Nat