Immunoglobulin immune complex reaction

A Type III allergic reaction occurs when antibodies of the immunoglobulin G class (IgG) form immune complexes which are slowly eliminated and thus may elicit an inflammatory reaction by binding to the Fey receptors of leukocytes resulting in their activation. 

There are thus various autoantibodies present, and if the auto-antigens are released by cellular breakdown, a type III immune reaction can occur where an immune complex is formed, which is deposited in small blood vessels and joints, giving rise to many of the symptoms. The immunoglobulins IgG and IgE act as both autoantibody and antigen, and hence immune complexes form. Such complexes stimulate the complement system leading to inflammation, infiltration by polymorphs and macrophages, and the release of lysosomal enzymes. 

The immunoglobulins have been extensively studied by ITP (in serum and csf see Section 2.4.4) and in particular the subclasses of IgG have been studied (H8, HIO, Hll, Z3). An extension of this work has been the demonstration of soluble immune complex formation in vitro (H9), which has obvious implications, particularly for the assessment of immune complex diseases. Preparative work has involved the isolation of, for example, antibodies to pig lactate dehydrogenase (B21, PI) and IgD myeloma protein (Jl). ITP has also been applied in the field of en-zymology, not for the direct measurement of enzymes as proteins, but for the determination of enzyme reaction substrates and products, and hence has been of use in enzyme kinetics. This work is summarized in Table 1. 

The immune complex transfer assay has allowed the development of very sensitive EIAs for the detection of antibodies. In one example, the assay utilizes a 2,4-dinitrophenyl (DNP)-biotin-conjugated antigen. This is incubated with the sample antibody to be measured, and, after the immune reaction, the immune complexes are trapped onto a primary solid phase coupled with anti-DNP antibody. After washing away unbound materials, immune complexes are eluted with DNP-lysine and transferred to a secondary streptavidin-coated solid phase. Next, an enzyme-labeled anti-immunoglobulin antibody is added, and, after washing, enzyme activity is assayed. In this case, the enzyme activity correlates with the amount of antibody in the sample. The sensitivity depends on the amount of nonspecific binding of the enzyme-labeled antibody on the second solid phase. Thus, several modified assay systems have been developed to reduce background. 

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