HP and rheumatoid arthritis: Specifically, dysfunction of the intestinal barrier, also known as “leaky gut”, has been postulated to be a crucial factor in the pathology of RA, as zonulin, a marker for intestinal permeability, has been found to be upregulated in the serum of individuals with RA-specific autoimmunity but without clinical arthritis as well as chronic RA patients compared to controls (Tajik et al., 2020).