Persistent retention of colitogenic CD4+ memory T cells causes inflammatory bowel diseases to become intractable.

Despite the advent of an age when "malignant" leukemia is cured by bone marrow transplantation, "benign" inflammatory bowel diseases (IBDs) are still intractable lifelong diseases. Why is it that once an IBD develops it lasts a long time? We propose that, the same as in the response to vaccination, immune memory T cells that remember the disease are formed in IBDs and, perceiving them as "benign T-cell leukemia"-like lifelong pathology that hematogenously spreads throughout the body, we here propose that the bone marrow itself, which produces large amounts of the survival factor IL-7, is the reservoir for colitogenic CD4(+) memory T cells responsible for the intractability of IBDs.