Significance of immunoglobulin G subclasses.

IgG subclasses differ from one another both immunochemically and functionally. An isolated absence of a certain specific subclass may or may not be associated with disease. However, an absence of serum IgG4 as measured by a sensitive radioimmunoassay is usually, if not always, associated with severe recurrent pyogenic infections, usually of the respiratory tract. IgG2 and IgG4 deficiencies tends to occur together, often in association with deficiencies of immunoglobulin A (IgA) and/or immunoglobulin E (IgE). The properties of IgG1 are similar to those of IgG3 and those of IgG2 appear to resemble those of IgG4 in certain respects. Specific combined deficiencies tend to be associated with certain diseases. Some patients with deficiency of an immunoglobulin G (IgG) subclass appear able to compensate and to avoid clinical disease whereas others are not. Overlap zones exist in the lower ranges of serum concentrations in which both healthy and immunoincompetent subjects are found. It is important to consider the concentration of each IgG subclass present in a gamma globulin preparation or in plasma used for replacement therapy. If specific antibody deficiencies exist, it may be critical that the preparation used for replacement contains goodly amounts of the missing antibodies.