Enzyme-linked immunosorbent assay and its application to the serological diagnosis of fungal infection

Abstract

With the introduction of the enzyme-linked immunosorbent assay (ELISA), a sensitive technique for detection and quantitation of fungal antibodies and antigens became available. Advantages of ELISA over existing serodiagnostic procedures in medical mycology include Ihe use of objective endpoints, the potential for rapid testing of body fluids and that the equipment necessary to preform basic assays can be both simple and cheap. This review outlines the bases and practical details of the different enzyme-immunoassay techniques and then examines the current status of ELISA procedures that have been applied to particular fungal infections in man and animals.Serological tests are useful as adjuncts to other means of diagnosis of serious fungal infection. These tests are based on the detection of the host's humoral immunological response to fungal infection, or on the detection of products of the fungus itself. Their usefulness depends on the reagents and methods used, on an understanding of their limitations and on judicious interpretation of test findings. Tests for precipitins or agglutinins are often used in the diagnosis of fungal infection [42]. They are useful in patients capable of producing normal levels of immunoglobulins, but are less helpful when applied to immunocompromised hosts where the immune response has been impaired. It is here that sensitive quantitative methods for detection of antibodies or antigen offer the greatest promise and it is not surprising that this field has received so much attention and investment of time.lmmunoassays in various forms have come to play a major role in the serodiagnosis of microbial infection [66]. Immunofluorescence has been widely used in the detection of antibodies and antigens in bacterial, viral and fungal infections. It is, however, rather subjective and labour intensive. In contrast, radioimmunoassay (RIA) is objective and can be automated. However, the reagents used often have a short half-life and there are legal restrictions on the use and disposal of isotopes. Enzyme-immunoassay (EIA), in which enzyme-labelled antibodies or antigens are used, is a more recent technique. Like RIA, it is objective and can be automated. Moreover, it is simple to perform, it is without obvious health risks and the reagents employed have a long shelf life which confers a marked economic advantage over RIA. Specific reagents are available for the detection of individual classes of human immunoglobulin. Established EIA procedures are time consuming but the methods are suited to the development of much more rapid tests. These considerations have led to the development of numerous EIAs, many of which are suitable for use in small laboratories without the need for sophisticated instrumentation.

Diagnosis of histoplasmosis

“…Several enzyme-linked immunosorbent assays (ELISA) protocols have been described for antibody detection using diverse antigenic preparations (113). An indirect sandwich ELISA for the detection of antibodies to H. capsulatum ribosomes and histoplasmin has been developed where antiribosomal antibodies were detected in 97% of histoplasmosis patients, but antibodies to histoplasmin were detected in only 75% of samples (110).…”

Candidosis: Diagnostic tools in the laboratory

“…Previously, it has been claimed that antibodies against proteinaceous fungal antigens may correlate with deep-seated mycosis (25), and the titer kinetics of certain candidal antibodies appear to possess prognostic value: Rising titers may predict a good outcome, while falling titers are associated with a fatal outcome (23,17). However, such correlation may simple reflect an overwhelming course of the infection (5):…”

Clinical laboratory applications of monoclonal antibodies

“…This section will focus on application of ELISAs in clinical microbiology, in particular, those assays that use MAbs. Many excellent reviews and books are available which cover the extensive ELISA development using polyclonal antibodies (20,26,33,71,89,118,141,176,185).…”