COW MILK PROTEIN ALLERGY
Allergy to milk protein is the abnormal reaction manifested by the body irrespective of the patho-genetic mechanism involved. Dictionaries define allergy as the sum of clinical symptoms like rhinitis, asthma, eczema etc. which appear after contact between an ‘antigen’ (for e.g. dust mites, pollen, cow’s milk, pig’s meat, barley etc.) and a specific antibody of the ‘epsilon’ class of immunoglobulins popularly known by its symbol IgE.
The IgEs are commonly seen attached on the surface of mastocytes and polymorphonuclear basophiles. It is the contact between the antigen and its specific allergen results in release of mediators like histamine that triggers the allergic reaction or the accelerated immune response. Many foods are known to harbour free histamines like tuna, mackerel, dark meat of different fish varieties including some of the seasoned cheeses. Other food items like tomato, strawberries, albumin and lecithin are capable of releasing the histamines through specific mechanisms which in turn causes the hypersensitivity. The degree of manifestation of allergic reactions vary depending on the individual; while some people are more prone to even a smaller quantity of biologically active agent (antigen) resulting in extensive reactions whereas certain people are more resistant to a higher threshold. Cow milk contains 20 different varieties of protein but only five are capable of inducing allergy. |
The five allergy inducing proteins are serum albumin, gamma globulin and alpha lactalbumin which are thermolabile; i.e. they can be easily destroyed by heat whereas the beta lactoglobulin and casein are thermostable; i.e. relatively heat resistant and capable of withstanding the proteolytic action of the gastric juice. The scenario would be completely different as far as digestion is concerned in case of infants. Because of insufficient secretion or lack of profound proteolytic activity in the GI tract of infants, the proteins are not completely broken down to its ultimate end product viz. amino acids and there is a risk of this unbroken proteins being considered by the body as an antigen.
The body has its own defense mechanism to prevent the entry of allergens (antigens) like anatomical barriers (epithelium, mucus) or immunological barriers due to the binding of secretory immunoglobulins with the invading antigens. This step may be considered as an important one as the antigen is prevented from accessing IgE. The newborn baby can well tolerate the maternal milk including the colostrum except in extreme metabolic disorders like phenylketonuria, galactosaemia or icterus etc.
But certain hypersensitive breast fed babies react vigorously to cow milk proteins especially the thermostable proteins like casein and beta lactoglobulin which are imbibed almost intact and recognized by the body as foreign body or antigen. Approximately 2-4 per cent of the adult population are cow’s milk intolerance and the condition is referred to as CMPA – Cow’s Milk Protein Allergy or Cow’s Milk Protein Intolerance while the incidence in breast fed babies vary widely between 1 and 8%. In industrialized countries, the major allergy suffered by the population is due to cow milk proteins. The allergic reaction to cow milk protein may be immunogenic or non-immunogenic.