Question

1. How does the immune system distinguish between food antigens and the antigens of invading bacteria that it must fight? (Describe 2 routes of Ag presentation of soluble food antigens)

2. Explain the mechanism of food allergy. How an oral tolerance can be breached?

Answer 1

Antigens are proteins that are found on the surface of the pathogen. ... The antibodies destroy the antigen (pathogen) which is then engulfed and digested by macrophages. White blood cells can also produce chemicals called antitoxins which destroy the toxins (poisons) some bacteria produce when they have invaded the body.

The immune system recognizes antigens.

Antigens are substances (usually proteins) on the surface of cells, viruses, fungi, or bacteria. Nonliving substances such as toxins, chemicals, drugs, and foreign particles (such as a splinter) can also be antigens. The immune system recognizes and destroys, or tries to destroy, substances that contain antigens

Antigen, a substance that is capable of stimulating an immune response, specifically activating lymphocytes, which are the body’s infection-fighting white blood cells. In general, two main divisions of antigens are recognized: foreign antigens (or heteroantigens) and autoantigens (or self-antigens). Foreign antigens originate from outside the body. Examples include parts of or substances produced by viruses or microorganisms (such as bacteria and protozoa), as well as substances in snake venom, certain proteins in foods, and components of serum and red blood cells from other individuals. Autoantigens, on the other hand, originate within the body. Normally, the body is able to distinguish self from non-self, but in persons with autoimmune disorders, normal bodily substances provoke an immune response, leading to the generation of autoantibodies. An antigen that induces an immune response—i.e., stimulates the lymphocytes to produce the antibody or to attack the antigen directly—is called an immunogen.

On the surface of antigens are regions, called antigenic determinants, that fit and bind to receptor molecules of complementary structure on the surface of the lymphocytes. The binding of the lymphocytes’ receptors to the antigens’ surface molecules stimulates the lymphocytes to multiply and to initiate an immune response—including the production of antibody, the activation of cytotoxic cells, or both—against the antigen. The amount of antibody formed in response to stimulation depends on the kind and amount of antigen involved, the route of entry to the body, and individual characteristics of the host.

Oral tolerance is a complex, active process that occurs in the gut-associated immune system. Although the precise mechanisms have not been completely elucidated, regulatory T cells seem to be essential for its development and maintenance. Other, overlapping mechanisms, including immune deviation, energy, and deletion, also play a role. Many factors affect the balance between allergy and oral tolerance. They include genetic variations, the dose, timing and route of antigen exposure, the microbial milieu, and probably other dietary factors. This field is still young, and much remains to be done to identify the mechanisms of allergic sensitization. Because of the complexity of the system, some things will not be known until interventional studies in humans are carried out.

Food antigen- When ingested food antigens bind to IgE on the surface of intestinal mast cells, causing an immediate hypersensitivity reaction. Basophils may also participate if food antigens appear in the circulation. Foods that commonly cause true food allergies include peanuts, true nuts, shellfish, eggs, milk proteins, and wheat. Cooking may destroy allergenic substances in some foods.

The prevalence of food allergy is increasing, and the development of more accurate diagnostic methods, prevention, and treatment require a better understanding of the underlying mechanisms. Oral tolerance is the normal physiologic response to ingested antigens, and a breakdown in this process results in sensitization to food allergens

ANTIGEN-SPECIFIC IMMUNE RESPONSE DEVELOPMENT TO FOOD ANTIGENS Sensitization to food antigens can take place in the gastrointestinal tract, oral cavity, and skin and occasionally in the respiratory tract. After ingestion, the vast majority of food proteins are broken down largely by gastric acid and digestive enzymes in the stomach and intestine. Subsequently, the remaining intact food proteins and peptides are transported from the lumen to the mucosa through gut epithelial cells (ECs) and by specialized ECs called M cells that are localized above Peyer patches. In addition, direct sampling of ingested antigens/allergens can occur when mucosal dendritic cells (DCs) extend dendrites into the gut lumen. In the mucosa, DCs internalize and process these proteins and peptides and move to T-cell areas of draining lymph nodes, where the DCs can interact with naive T cells and present antigen on MHC class II molecules The activation of anaphylaxis by targeting mast cells.5 Migration and activation of intraepithelial lymphocytes, including gd T cells, also occurs in response to allergic sensitization in mice. Recently, it was reported that injection of a mAb to IL-25, IL-33 receptor or thymic stromal lymphopoietin strongly inhibited food allergy development in mice. Administration of a single mAb targeting either of these cytokines could not suppress established food allergy and optimal food allergy suppression required treatment with a cocktail of all 3 anti– pro-TH2 mAbs.