Immunodiagnosis Detection of Antigens in Body Fluids

Abstract

Rapid, sensitive methods have been developed to detect antigens which appear in body fluids during infections due to a wide variety of infectious agents. Antigens that are currently detectable include those of hepatitis B surface antigen, dengue, coxsackie A, and rotavirus; the capsular polysaccharides of Hemophilus influenzae types a–f, pneumococci of many types. Neisseria meningitidis groups A, B, C, and Y, Klebsiella of many types, Escherichia coli strains, Pseudomonas aeruginosa, group B streptococcus (Streptococcus agalactiae), Staphylococcus aureus, and Cryptococcus neoformans; antigen from Rickettsia prowazekii; and endotoxin. The purpose of this chapter is to review the newer methods of antigen detection, the problems associated with their use, their application in various clinical situations, and potential areas of future application. Specifically, the methods to be discussed include the precipitin tube test; countercurrent immunoelectrophoresis (CIE); agglutination tests, including latex agglutination (LA), hemagglutination inhibition (HI), and passive hemagglutination (PHA); the radioimmunoassay tests (RIA); the enzyme-linked immunosorbent assay (ELISA); and the limulus lysate test (LT). Table 1 shows which tests have been applied to each of the above antigens. None of these tests requires the presence of living or whole-killed infectious agents for the detection of antigen in body fluids. Staining, quellung, agglutination, and fluorescent labeling of whole organisms free in body fluids or attached to cells are not the subjects of this chapter. Since the complement-fixation test is rarely used, it will only be referred to in the discussion of other methods.