A Review of In-Vitro Assays for IgG and IgG₄ Antibodies: Concept and Potential Applications

In-vitro assays for the diagnosis of allergy presently are quite common, having been demonstrated by a number of investigators to possess a high degree of specificity and sensitivity. These assays are for the most part rapid, flexible, and when utilized properly, cost effective.

It has long been known that antibodies, other than the homocytotropic antibodies, are involved in allergy. The concept of "blocking antibodies" was first introduced by Cooke in 1935. He demonstrated that these antibodies could neutralize the effects of reagins present in the sera of allergic individuals. Since that time investigators have developed a series of techniques to assess and define blocking antibodies. These techniques include inhibition of antigen-induced histamine release from peripheral blood leukocytes, hemagglutination with allergen coated erythrocytes, radio-allergo-sorbent test (RAST), define antigen substrate sphere (DASS), antigen binding radioimmuno assay, and more recently, enzyme-linked immunosorbent assays (ELISA). These methods have been utilized to show that "blocking antibodies" are predominantly of the IgG class.

Recently, several assays have been introduced to the clinical laboratory for the purpose of monitoring the production of blocking antibodies (i.e., IgG) in response to immunotherapy. These assays, while adding an important tool to the arsenal of the clinical practitioner, may have limited utility because of a lack of specificity and sensitivity. Recently, 3M Diagnostic Systems (3MDS) has introduced an assay via its Reference Laboratory designed for the measurement of what many investigators feel is the appropriate marker for monitoring immunotherapy… the IgG₄ subclass. This assay offers a high degree of specificity and sensitivity. Today we will discuss this assay and its possible utility.