They are an important aid in monitoring immunotherapy. The quantification of allergen-specific IgG4 antibodies in serum provides an appropriate assessment of the immune response. IgG4 has the ability to regulate the immune response to the allergen and therefore has the potential to influence the clinical response. Valuable clinical information can be obtained regarding allergic disease and immunotherapy. The measurement of specific IgG4 antibodies has also been used in clinical studies of different allergic diseases such as asthma, rhinitis, atopic dermatitis and gastrointestinal disorders. It is an important indicator for monitoring allergen immunotherapy (AIT). During immunotherapy, elevated levels of specific IgG4 may indicate: A general, but not definitive, correlation with clinical outcome. That the immune system is responding to treatment. There is no common cut-off value for above normal levels of circulating specific IgG4 antibodies, as these are indicators of allergen exposure, which may not be directly related to the disease and will depend on the local environment and exposure levels.