Diagnostic procedures in immunodermatology

Most immunologic diseases are caused by the derailment of the humoral or cellular pathways of the immunologic defense system. This derailment results from numerous factors such as the inability of the patient to remove the pathogen; the consumption, defect, or deficiency in any component of these pathways, and the overproduction of any of the components. To diagnose these immunologic disorders one has to detect the pathogen and the reactions caused by it and to determine the cause of its nonclearance. The immunofluorescence techniques has been invaluable in detecting both the antigen that causes the disease and the reactions initiated by the antigen, such as the production of antibodies and the activation of the complement system. The immunoperoxidase technique has also been used for these purposes in certain instances. For detecting the circulating immune complexes which occur as intermediates in the chain of reactions initiated by the antigen, various physiochemical and biologic techniques have been used. However, none of these tests seems to be totally reliable for determining whether circulating immune complexes are present. The consumption of complement was detected by hemolytic estimations and radial immunodiffusion or rocket electrphoresis. These techniques were also useful in detecting the hereditary deficiencies in immunoglobulins and components of classical and alternative pathways of complement activation. Since these techniques cannot be used to estimate IgE, the radioallergosorbent test was used to measure such levels in the atopic patients. Cellular hypersensitivity was detected with skin tests together with methods which assess the ability of lymphocytes to produce mediators in response to antigen. Many of these mediator assays, however, are not suitable for this purpose. A satisfactory substitute appears to be to determine the factor in antigen-stimulated, lymphocyte culture supernatants which activates macrophages to take up radiolabeled colloidal gold or radiolabeled glucosamine. In contact allergic dermatitis, an increase in the IgD-bearing lymphocytes and granulocytes has also been correlated with cellular hypersensitivity. Lymphocytes and polymorphonuclear leukocytes coated with antibodies mainly directed against nuclear antigens of the basal layer cells of the noninvolved epidermis have invariably been encountered in psoriasis. The use of these findings for diagnostic purposes and for understanding the mechanisms of certain diseases is being explored.