I think I've just found the connection.
"Since white blood cells involved in the immune process are the cells that release various chemicals can result in increased intestinal permeability, the presence of increased numbers of these cells are a microscopic clue that the gut is leaky. Typical cells seen are lymphocytes but may also include eosinophils and mast cells in certain conditions. These cells release chemical mediators that attract more cells to the area. Lymphocytes in particular release a chemical tumor necrosis factor (TNF) that increases the numbers of lymphocytes in the villi."