Critical evaluation of the clinical relevance of the IgG subclasses assays.

Human IgG subclasses play a major role in the physiological regulation and functions of the immune system. There "personality" is obvious. However, the determination requires appropriate reagents and technology. For the IgG1, IgG2, IgG3 subclasses, the radial immunodiffusion technique may be sufficient. For the IgG4 subclass determination and measurement, more elaborate techniques are required. These measurements of existing proteins are of major interest in congenital as well as acquired immune deficiencies more often, besides the total subclass deficiency, these are of utmost interest to evaluate the specific response of a given subclass to a specific antigen. The IgG4 allergen specific subclass has been considered to be involved both in allergic reactions and associated with the appropriate response to allergen-specific immunotherapy. It is now accepted that IgG4 does not play an discernable role in the acute inflammatory response of type I hypersensitivity; it has also been demonstrated that a number of patients who demonstrate elevated levels of allergens specific IgG4 are not protected against allergenic exposure, and conversely, a number of patients who have been heated by immunotherapy without demonstrating any significant increase in their serum levels of allergen specific IgG4 are indeed very well protected. In the field of allergy, the IgG4 determinations remain a matter of controversy and research.