Helminthic Therapy - Theoretical Explanation

Theoretical Explanation

Although the mechanism of autoimmune disease development is not fully defined, there is broad agreement that the majority of autoimmune diseases are caused by inappropriate immunological responses to innocuous antigens, driven by a branch of the immune system known as the TH1 type immune response. Extra-cellular antigens primarily trigger the TH2 response, as observed with allergies, while intracellular antigens trigger a TH1 response. The relationship between these two types of immune response is a central theme of the hygiene hypothesis, which suggests that there is a regulatory action between the two types of response. However, the observation that allergies and autoimmune response are increasing at a similar rate in the industrialized nations appears to undermine the hygiene hypothesis.

A refinement of the hygiene hypothesis, which overcomes this apparent contradiction, is the "old friends hypothesis." The old friends hypothesis modifies the hygiene hypothesis by proposing that T regulator cells can only become fully effective if they are stimulated by exposure to microorganisms and parasites that have low levels of pathogenicity, and which have coexisted universally with human beings throughout our evolutionary history. This theory has recently been given more credibility by a study demonstrating the impact of infectious organisms, and helminths in particular, upon genes responsible for the production of various cytokines, some involved in the regulation of inflammation, in particular those associated with the development of Crohn's Disease, ulcerative colitis, and celiac disease.

The hygiene hypothesis proposes that appropriate immune response is in part learned by exposure to these microorganisms and parasites, and in part regulated by their presence. In the industrialised nations, humans are exposed to somewhat lower levels of these organisms. The development of vaccines, hygienic practices, and effective medical care have diminished or eliminated the prevalence and impact of many parasitic organisms, as well as bacterial and viral infections. This has been of obvious benefit with the effective eradication of many diseases that have plagued human beings. However, while many severe diseases have been eradicated, humans' exposure to benign and apparently beneficial parasites has also been reduced commensurately. The central thrust of the theory is, therefore, that correct development of T regulator cells in individuals may depend on exposure to organisms such as lactobacilli, various mycobacteria, and helminths. Lack of exposure to sufficient benign antigens, particularly during childhood, is sometimes suggested as a cause of the increase in autoimmune diseases and diseases for which chronic inflammation is a major component in the industrialized world.