Helminths, Oligosaccharides and Immunotolerance

Parasitic worms reverse allergies and autoimmune diseases using oligosaccharides to mimic self and silence immune over-responsiveness.

Helminth therapy, i.e. infection with parasitic intestinal worms to provide remission from allergies, inflammatory bowel and other autoimmune diseases, has been examined as a potential therapeutic model to rehabilitate immunological dysfunction.  The surface oligosaccharides of these worms have been found to mimic human oligosaccharides and alter immune responses by binding to carbohydrate-binding, i.e. lectin, receptors.

Immune Tolerance
The essence of allergic and autoimmune diseases is a defect in distinguishing between pathogen, innocuous and self molecules.  Heightened immune reactions as a result of inflammation move the immune system toward production of antibody and T cell receptors specific for antigens.  Those antigens respond to unique receptors on the surface of each B and T lymphocyte.  The lymphocyte population has been previously depleted of cells that can produce receptors that will bind to most self antigens.  This depletion makes the lymphocyte population generally non-responsive, or tolerant to self antigens.  Thus, the immune system is blind to the body.

Regulatory T Cells and Tolerance
Most of the immune cells of the body are present in the lining of the gut.  It is in the gut that various immune cells continue to develop for their various roles, including controlling immune reactions to self antigens and to common food molecules.  Immune cells in the gut are exposed to some food molecules and bacteria that leak through the cells of the intestinal villi.  Responding to these common antigens by inflammation can lead to inflammatory bowel disease.  This pathological over-responsiveness is normally avoided by development of regulatory T cells, Tregs, that suppress immune responses to common food molecules and to surface antigens of common bacteria.

Treg Development Depends on Gut Flora
Gut bacteria are needed for the normal function of the immune system.  Oddly, Helicobacter pylori, Hp, the cause of stomach ulcers and cancer, also stimulates the development of Tregs.  Thus, the pathology of Hp may result not from its presence, but rather from how it is growing.  Since Hp uses hydrogen gas produced by Klebsiella in the lower bowel and hydrogen production is dependent on dietary starch, then it follows that the pathological behavior of Hp may be dependent on dietary starch.  A low starch diet may actually result in Treg stimulation from Hp and a reduction in allergies and autoimmune diseases.

Tregs Enhanced by Heliminths
Immunological tolerance is also stimulated by parasitic worms, Helminths.  Helminth infestations, therefore, reduce allergies and autoimmune diseases and may contribute to the hygiene hypothesis to explain the prevalence of allergies, autoimmune and other inflammation-based degenerative diseases in modern societies.  Examination of worms to find the molecules responsible for inducing immunological tolerance has identified complex surface and secreted oligosaccharides (small sugar chains) as the active molecules.  Helminth oligosaccharides mimic human cell surface oligosaccharides and bind to carbohydrate-binding, lectin, receptors on immune cells to stimulate Treg development.

Lectin Receptors Control Tolerance
There are many implications of the modulation of the immune system via oligosaccharides.  Note that related oligosaccharides are components of human milk and prepare the gut and develop the immune system.  This explains why formula, which lacks these unique oligosaccharides, results in aberrant gut flora, contributes to neonatal necrotizing colitis and supports the development of allergies and autoimmune diseases.  In contrast, judicious use of self or Helminth oligosaccharides may provide a means of restoring the function of damaged immune systems and therapy for allergies and autoimmune diseases.  Also note that the critical use of lectins, which have oligosaccharide-binding sites rich in aromatic amino acids to bind the hydrophobic faces of the sugars, will also bind and provide entry into immune cells for allergens and autoantigens that have triplets of basic amino acids.  The binding sites of lectins should also bind many aromatic phytochemicals.  Immunomodulation by phytochemicals may result from interference with or mimicking the binding of oligosaccharides to lectin receptors.

reference:
van Die I, Cummings RD.  Glycans modulate immune responses in helminth infections and allergy.  Chem Immunol Allergy. 2006;90:91-112.

Lectins - Heat’em and Eat’em

Lectins are proteins common in seeds. They bind to sugars attached in chains to proteins, i.e. glycoproteins, and are displayed on the surfaces of cells that line the gut. Lectins could inhibit digestion of raw beans, but cooking makes them digestible.

Fear of lectins is puzzling. Lectins are proteins that have binding sites on their surfaces for specific single or small sequences of sugars. They are present in seeds to protect the seeds from herbivores.

A seed is mostly food (starch, protein, fat) for the plant embryo that will grow from it. This is also true of a chicken egg and just like the egg, the seed contains defensive proteins to inhibit the growth of bacteria, fungi and egg/seed eaters.

The egg has enzymes to degrade bacterial walls and proteins that bind iron, vitamins, etc. needed by bacteria and humans. Eating many raw eggs can lead to vitamin deficiencies. Boiling the eggs, unravels the defensive proteins and makes them digestible and nutritious.

Seeds block being digested by containing proteins that foul the digestion system of would be devourers. For example, soybeans have trypsin inhibitor that binds to our digestive enzyme and makes eating raw soybeans nonproductive and uncomfortable. Boiling soybean meal to produce a curd, i.e. tofu, agglutinates the denatured soy proteins, including the lectins and washes away the soy trypsin inhibitor. Tofu is free of digestion inhibitors and lectin activity.

It is not an accident that lectins bind to human red blood cells. The sugars displayed on the surface of red blood cells are the blood group antigens. Different sugars on the end of the sugar chains decorating RBCs characterize the A, B and O antigens. These same sugars are present on the surfaces of various bacteria. Immune systems don’t produce antibodies to self antigens, so a person with type A blood produces antibodies only to B antigen sugars it encounters on bacteria. A person who is type AB doesn’t produce antibodies to A or B sugar antigens. There aren’t antibodies to O, because that sugar structure is the basis upon which both A and B are made, and some of the
structure is present on all RBCs. Lectins are specific for A or B or other common bacterial sugar antigens.

I did some modeling to show a lectin with lactose (red and gray) bound to sticky tryptophans (yellow) in two places on the surface. In one case a lysine (blue) is draped on the other side. That shows that sugars bind both to aromatic amino acids and to the hydrophobic arms of basic amino acids.


Some people think that humans and other mammals must be protected from lectins and that this protection is shown in human and cow’s milk in the form of antibodies against lectins. This seems to be a misunderstanding. For example, human antibodies secreted in breast milk are secretory IgAs. These antibodies are glycoproteins, i.e. they are proteins with attached sugar chains. Some lectins will bind to these antibodies, because of the attached sugars. These are not lectin-specific antibodies, but rather glyco-specific lectins. The lectins are binding to the glycoprotein antibodies, not the other way around.

It is possible for people to be allergic to lectins, but this is unlikely. For example, peanut allergies involve proteins other than the peanut lectins.

There are some dangerous lectins. For example, ricin is a very nasty, but effective, toxin produced by the castor plant. Ricin is a lectin, in that it binds very specifically to sugars found on the surface of gut cells of insects and humans. After the ricin binds to surface proteins, it is brought into the cells where it chops up the protein synthesizing machinery. That is a dangerous lectin. It takes very little ricin to kill each cell and only a tiny amount to kill a human. Ricin is a terrorist toxin. Yet oil extracted from castor beans contains so little contaminating ricin that it is safe to eat. [Castor oil is wonderful to apply to aching feet overnight for painfree, luxuriously soft feet in the morning.]

The bottom line is that seed lectins add to the nutrition of cooked beans and grains that have been the foundations for several thriving civilizations. The longest living members of the bean and grain cultures are typically older and more fit than comparable individuals with a modern, inflammatory diet based on omega-6 oils.