Cow milk allergy and the mechanisms of food allergy

A food allergic reaction occurs as a result of some component of the immune system, which normally protects us from infectious agents, inappropriately reacting to the proteins in foods we eat. Food allergic diseases usually occur in the first decade of life and are directly linked to the maturation of the immune system. In general, clinical symptoms are not detected at birth and although the production of IgE starts in the eleventh week of gestation, no specific sensitization to food allergens can be detected in cord blood.

During the first months of life initial IgE responses to food proteins, particularly hen’s egg and cow’s milk may be observed even in exclusively breast-fed infants. In such individuals, it is proposed that exposure occurs through proteins in their mother’s milk.

Allergic reactions to foods can be broadly divided into immediate on-set and delayed on-set reactions.

IgE-Mediated Food Allergies

The parts of the immune system responsible for immediate on-set reactions (the most dramatic example of which is food anaphylaxis) are IgE antibodies.

In allergic individuals (who are sometimes referred to as being "atopic") eating certain food proteins (such as whey and casein protein contained in cow’s milk) results in the production of specific IgE antibody molecules directed against the protein. The second time the individual eats the food, these specific IgE molecules interact with each other, and the protein, to cause the release of harmful chemicals (such as histamine) from special mast cells. This causes the damage associated with the symptoms of food allergy. Damage may occur to the skin, respiratory system or gastrointestinal tract, where the symptoms of food allergy are almost exclusively seen.

Non-IgE-Mediated Food Allergy

"T-cells" are the components of the immune systems responsible for delayed-type food allergic reactions. In individuals with a predisposition for delayed on-set food allergy, initial ingestion of food protein leads to the production of specific types of "T-cell". When the food is subsequently ingested, the food protein is "processed" in a variety of ways and "presented" to the previously generated food-specific T-cells. These T-cells then "invade" the area of the body about to suffer damage, as the skin or the bowel. This processing, presenting and invasion can take 24-48 hours which explains the delayed response. T-cells release chemicals that, through a chain of events, lead to the damage associated with symptoms of food allergy.

Infants and Cow Milk Allergy

Cow milk allergy (CMA) is a reaction to cow milk that results from a hypersensitive immune response to one or more milk proteins.

Milk is the most common cause of food allergy affecting a minimum of 2-3% of infants. However symptoms suggestive of cows’ milk allergy may be present in up to 15% of babies, highlighting the importance of getting an accurate diagnosis.

Most babies with cow milk allergy develop symptoms within the first few months of life. It is rare for symptoms to begin after the age of 12 months.

Symptoms of cow milk allergy can be:

• skin symptoms, (e.g. eczema and rash),
• stomach or gut symptoms (e.g. vomiting, diarrhea or constipation)
• breathing symptoms (i.e. wheezing)

Most babies with cow milk allergy will have two or more symptoms.

The recommended management approach to cow milk allergy is to completely avoid cow milk protein. Because milk is an important food for infants, cutting it out from a baby’s diet may put them at risk of poor growth. This risk can be overcome with an alternative hypoallergenic formula, such as amino-acid based formulas (AAF) or extensively hydrolyzed formulas (eHF), which can provide rapid relief of symptoms and enables optimal growth and development.

(Source: Act Against Allergy: February 2008)