Some pulmonologists want to follow IgG4 concentration of the allergen during desensitization because IgG4 must increase for good result. This test is often contested.
This response is based on an excellent presentation in UpTo Date:
High levels of allergen-specific IgG as a result of SCIT do not necessarily correlate with clinical relief of symptoms. However, the failure to produce allergen-specific IgG in an individual patient receiving immunotherapy does predict a lack of clinical response This finding can be used clinically to assess the efficacy of a patient's previous immunotherapy. If the patient reports that a previous course of SCIT did not seem to help, the finding of low allergen-specific IgG levels to the allergen given essentially confirms that the therapy was not effective.
Despite data suggesting that IgG4 is important for successful SCIT, not all studies have found that increases in this isotype correlate with clinical improvement. In a retrospective review of six immunotherapy studies, only two found an association between increased IgG4 and clinical benefit . Thus, simple measurements of the levels of allergen-specific IgG4 do not correlate with clinical success. It may be that some type of functional assays of allergen-specific IgG, such as detection of IgG-associated serum inhibitory activity for IgE-facilitated allergen presentation, basophil histamine release, or both, might be more closely associated with the clinical response to immunotherapy, although this remains to be tested.
I hope this will be an answer some of your question.
I think you would need to look at multiple factors such as FcgR polymorphisms as well as at IgG levels. For example IgG4 interacts with the high affinity form of FcgRIIIa and thus can mediate activation of cells expressing that polymorphism. Thus you could easily find that IgG4 was inhibitory in some individuals and activatory in others.
Many laboratory tests have been suggested and studied as candidates for a marker of AIT efficacy. Serum IgG4 level is one of them. However there are no sound evidence based data that we can use just one particular test to predict and assess AIT results. That is the reason why allergists have accepted that total symptom score, medication usage score and quality of life are the markers for AIT efficacy.
For an individual patin, the assay of the IgG4 antibodies againts a specific allergen has no value to follow the immunisation. In a group of patients desensitized the rise of specific Ig4 associated to the decrease of the speciific IgE demonstratthe potency of the traitement. In individuals suspected of food allergy the assay of specific IgG (IgG4) is without diagnostic value. Many Allergologic Societes have pointed this fact.
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