There are a lot of foods that can provoke an allergy. Peanuts, nuts (walnut, almond, cashew, hazel nut, Brazil nut) and crustaceans are the foods most often responsible for food-induced anaphylaxis.
When breast-feeding is not an option, hydrolysed cow’s milk products and soya milk formula are good alternatives in case of cow's milk protein allergy. Cow's milk protein allergy is usually diagnosed before the age of 1 year.
Mechanism
A food allergy is provoked by a disorder of the immune system; the immune system then reacts to certain substances in the food as if they were hostile organisms, such as dangerous bacteria. The substances, which the hypersensitive persons react to, are called “allergens” and most allergens are proteins.
The immune system reacts against these allergens by producing antibodies or immunoglobulins (Ig). In case of food allergy these antibodies are of the IgE type. For infections, other types of antibodies are formed, eg. IgA, IgG, IgD and Ig M.
The first time the allergen is eaten, there are often no symptoms, but several antibodies are usually formed. This stage is called the sensitisation phase . The next time the allergen is eaten, the typical IgE antibodies provoke a whole battery of immune responses and they cause the typical symptoms of a food allergy.
The IgE antibodies do not directly attack the antigen, but they send a signal to the mast cells, and these release a large amount of histamine. It’s the histamine that is responsible for the sudden inflammatory symptoms that can include inflammatory reaction on the skin, mucous membranes, muscles or the respiratory tract.
Cow’s milk protein allergy
Cow's milk allergy is a real food allergy (Type I), IgE mediated. The most important allergens in cow's milk are casein, beta-lactoglobulin, alpha-lactalbumin and bovine serum albumin.
Symptoms occur shortly after ingestion and include skin reactions (erythematous lesions), angioedema, Quincke-oedema, respiratory problems (asthma, allergic rhinitis) and gastro-intestinal symptoms (vomiting, diarrhoea) (1,2). In some cases anaphylaxis can occur, with possible life-threatening consequences (3).
Other early, but no life-threatening symptoms of food allergies are: itching (purities) in the mouth, a tingling sensation in the lips, mouth and respiratory tract, nausea and vomiting, a burning skin or red spots (hives or urticaria).
More serious and life-threatening symptoms can progressively appear, such as swelling of the mucous membranes in mouth and throat, low blood pressure and shock, cardiac rhythm disturbances and severe bronchospasm. For cow’s milk allergy these severe symptoms are rare and in most cases patients suffer from stomach and intestinal problems, such as cramps, nausea, vomiting, and diarrhoea. Raches (eczema) are also possible and respiratory tract disorders occur to a lesser extent.
Symptoms mostly disappear in children older then one year. Most children with a cow’s milk allergy tolerate cow’s milk again when they reach the age of three years.
After intake of milk products, protein is broken down into peptides and amino acids. The degree of breakdown by the proteases in the gastro-intestinal tract plays an important role. Before the age of one year, the proteolytic activity of these enzymes is still incomplete.
As a consequence, some of these macromolecules (antigens) pass through the intestinal mucosae and reach the antibody-producing cells. Antigen-specific Ig A 's are formed; these can form complexes with the antigen and thus prevent further absorption. In babies the secretion of IgA can be relatively low, which will give rise to an enhanced gastro-intestinal permeability. If the antigen does penetrate further, other immuno-competent cells are encountered and IgE antibodies formed. On renewed contact with the antigen, an allergic reaction then occurs.
In most people the passage of the antigens through the intestinal wall will cause no problems since normally a systemic tolerance for food antigens exists. The allergy occurs when one or several of the mechanisms involved in this tolerance
fail. Damage to the intestinal wall can also be responsible for increased
penetration of food allergens. A food allergy can occur after an intestinal infection. When an allergy occurs, the food antigen interacts with the IgE molecules on the mast cells. These mast cells degranulate and release a series of mediators, such as histamines and leucotrienes that cause the ultimate symptoms.
In the case of cow's milk allergy without damage to the intestinal membrane, soya drink can be a good alternative.
References
- Casimir. L'allergie alimentaire chez l'enfant. Allergoguide n¡ 4.
- Sicherer. Manifestations of food allergy: evaluation and management. American Family Physician 1999 Jan 15; 59(2): 415 24,429-30.
- Novembre et al. Anaphylaxis in children: clinical and allergologic features. Pediatrics 1998; 101(4).