Conjugation of enzymes to anti-poliovirus globulin: effect of enzyme molecular weight on virus neutralization capacity

Enzyme-linked immunoassays for the detection of microbial antigens and their antibodies

Antibodies could be labeled with enzymes for use in histochemical staining procedures by enzyme-immunoassay (EIA). The use of EIA is an extension of previously used serological tests, using enzyme-labeled antibody or antigen to determine antibody content. Direct detection of antigen by EIA represents a more dramatic departure from previous methods based on culture. Also, the method has enabled detection of infectious agents that are difficult to cultivate, such as hepatitis A virus and rotavirus, or agents that cannot be cultivated, such as hepatitis B. The use of EIA tests for detection of microbial antigens provides an alternative to culture as a means for direct identification of a specific microbial agent. It also provides a means to detect microbial agents which have not been successfully propagated. The detection of circulating antigen or detection of antigen in other body fluids by EIA is more difficult than detection of antibody because of the sensitivity required, and because of interfering substances in specimens such as feces and respiratory secretions. For this reason, very few antigen detection assays have the sensitivity and specificity required to be used as a primary diagnostic test. The number of tests that have been developed, however, is impressive and because of the possibilities for rapid, specific diagnosis, the interest in antigen detection by EIA remains high.

Critical density for protein-protein monoconjugation on a polysaccharide matrix

The galactose binding toxin (RCAII) from Ricinus communis was affinity-immobilised at varying densities on a polysaccharide matrix and reacted with glutaraldehyde. The critical density below which inter-molecular cross-links were not formed was determined. At this density RCAII was monoconjugated to lysozyme. This approach could serve as a prototype for enzyme-lectin and enzyme-antipolysaccharide antibody monoconjugation.

Comparison of techniques and immunoreagents used for indirect immunofluorescence and immunoperoxidase identification of enteroviruses

Peroxidase-conjugated antibodies were found to be as sensitive as those conjugated to fluorescein-isothiocyanate (FITC) for identification of selected enterovirus types by the indirect technique. Peroxidase conjugates, however, were found to give fewer nonspecific reactions. The reasons for the higher specificity of the immunoperoxidase technique appear to be related to the relative size, charge, and uniformity of the preparations. Monomers of peroxidase-conjugated globulin are larger than those of FITC conjugates, but the latter readily form aggregates. This was shown by chromatography on Sepharose 6B columns: various FITC-conjugated globulins eluted before those conjugated to peroxidase and before (125)I-labeled immunoglobulin G. The net charge of the conjugates was determined by adsorption to ion-exchange columns. FITC-labeled globulins had a negative net charge, eluting at pH 5.1 from diethylamino-ethyl-Sephadex A-50 columns. Peroxidase conjugates were not retained by either cationic or anionic exchangers at pH values ranging from 4.0 to 10.5. Further, the fluorescein/protein ratios of FITC conjugates from different commercial sources and of those prepared in the laboratory were found to be variable; higher fluorescein/protein ratios (>2:1) give a higher degree of nonspecific reactions, whereas the peroxidase/protein ratio does not appear to affect specificity. These characteristics of peroxidase conjugates make the immunoperoxidase technique easier to standardize and more reliable for enterovirus identification than the immunofluorescence technique.