HelminthsAn intestinal worm which grows large enough to be seen with the naked eye when mature but which is microscopic when administered in helminthic therapy. [https://en.wikipedia.org/wiki/Helminths Wikipedia:Helminths] evoke a TH2 response, which up-regulates the intestinal repair rate and thereby helps improve mucosal barrier integrity.
We propose a model whereby the immune response that is triggered to expel gastrointestinal parasites ... may have a beneficial effect in restoring mucosal barrier function... 
What is unique about parasites is that they probably have evolved (and we evolved with them) to have a response that promotes re-establishment of barrier integrity while not damaging or causing problems with the host at uninvolved sites. Without parasites, for whatever reason, this barrier maintenance machinery that is always in the background runs in overdrive, and there is no brake on the system. It is reacting to barrier damage and leading to an overexuberant response to that damage signal. 
Host protective immunity has adapted to enteric parasitic nematodeA category of worms with slender, unsegmented, cylindrical bodies that include roundworms and threadworms.
infection by elaboration of mucins, increasing intraluminal fluid to control access to the surface epithelium, increasing cell turnover to maintain an effective barrier to their invasion, initiating immune responses through activation of resident immune cells, and recruitment of additional immune cells to release immune mediators that help orchestrate these responses. 
At least three helminth self-treaters have seen an improvement in their leaky gut syndrome after commencing the therapy.
My husband seemed to have severe lactose intolerance. In the past, nothing helped and it was instantaneous, as in explosive diarrhea and severe within 20 minutes of ingestion. Since his leaky gut has gotten better since getting worms, he's doing a lot better, so that he can actually digest ice cream. 
At six and half months in (25-25-40 HWhookworm, usually referring to the human hookworm, Necator americanus
) I am just short of claiming success for multiple food intolerances, likely leaky gut and a host of other related symptoms. I couldn't eat gluten or dairy without debilitating symptoms and had been GF DF for 7 plus years. For the past three weeks I have eaten anything I wanted for one meal a day without the terrible symptoms I have experienced all my life. 
NAthe human hookworm, Necator americanus
helped my leaky gut. 
Helminthic Therapy Wiki: documenting the science, management, experience and results of helminth replacement therapy.