A multiplexed and miniaturized serological tuberculosis assay identifies antigens that discriminate maximally between TB and non-TB sera.

We have developed a multiplexed and miniaturized TB serological assay with the aim of identifying (combinations of) antigens that maximally discriminate between TB and non-TB patients. It features a microarray accommodating 54 TB antigens, less than 1 microl serum consumption and an indirect immunofluorescence detection protocol. With a panel of 20 TB and 80 non-TB sera we ranked combinations of TB antigens with respect to sensitivity and specificity of TB detection by means of logistic step-forward regression analysis. The highest-ranking TB antigen combination had an area-under-the-curve of the receiver-operator-characteristics (ROC) of 0.95. We also identified an antigen that on its own provided good specificity and sensitivity of TB detection (Ara6-BSA; area-under-the-ROC curve: 0.90). These area-under-the-ROC curve values are exceptionally high for a serological TB assay. We conclude that TB antigen microarrays permit rapid identification of TB antigens that, either alone or in combination, discriminate maximally between TB and non-TB patients and that such identification provides an excellent starting point for developing point-of-care diagnostic assays.

Enzyme-linked immunosorbent assays using immune complexes for the diagnosis of tuberculosis.

The serodiagnosis of tuberculosis has long been the subject of investigation, but we still lack a test with widespread clinical utility. The poor sensitivity and specificity of commercial assays precludes their use as the sole means of diagnosis. All of these assays use mycobacterial antigens adsorbed onto a surface. Little attention has been paid to changes in antigen conformation that may occur as a result of passive coating of these antigens to solid supports like polystyrene. Such changes may cause technical artifacts resulting in false-positive (FP) and false-negative (FN) reactions. We have developed two different enzyme-linked immunosorbent assay (ELISA) systems, in which human serum antibodies and target antigens of Mycobacterium tuberculosis are able to associate and dissociate freely in solution to form immune complexes. In one ELISA, rabbit antibodies against M. tuberculosis, passively coated in the ELISA wells, capture the immune complexes (ICs). In the other ELISA, the ICs are detected by these same rabbit antibodies but are first captured by passively coated goat anti-rabbit IgG. We have compared these two ELISA systems with an ELISA using M. tuberculosis antigens passively adsorbed to the solid polystyrene surface of the plate. We studied sera from 81 patients with tuberculosis and 47 healthy subjects. The differences between tuberculosis (TB) patients and healthy subjects were statistically significant in all three of our ELISA systems. However, the ELISA systems using soluble M. tuberculosis antigens distinguished better between TB patients and healthy subjects than the ELISA using surface-adsorbed M. tuberculosis antigens. We suggest that in the latter ELISA, passive adsorption of the target antigens induces conformational change, generating altered epitopes that are recognized by antibodies present in the serum from even healthy people. These altered conformational epitopes are recognized by antibodies that were originally evoked by antigens other than M. tuberculosis, known as heterophile antigens.

Use of horseradish peroxidase- and fluorescein-modified cisplatin derivatives for simultaneous labeling of nucleic acids and proteins.

BACKGROUND: Microarray platforms will change immunochemical and nucleic acid-based analysis of cell homogenates and body fluids compared with classic analyses. Microarrays use labeled target and immobilized probes, rather than fixed targets and labeled probes. We describe a method for simultaneous labeling of nucleic acids and proteins. METHODS: Horseradish peroxidase- and fluorescein-modified cisplatin derivatives were used for labeling of nucleic acids and proteins. These reagents, called the Universal Linkage System (ULS), bind to sulfur- and nitrogen-donor ligands present in amino acids and nucleotides. For automated screening of proteins and nucleic acids on microarrays, it is advantageous to label these biomolecules without pre- or postpurification procedures. The labeling of antibodies and nucleic acids in whole serum was therefore pursued. RESULTS: Immunoglobulins in nonpurified serum were labeled efficiently enough to be used for immunochemistry. To investigate whether protein-adapted labeling allowed nucleic acid labeling as well, 1 microg of plasmid DNA was added to 1 microL of serum. DNA and serum proteins were simultaneously labeled, and this labeled DNA could be used as a probe for direct fluorescence in situ hybridization. CONCLUSION: ULS provides a direct labeling tool for the (simultaneous) modification of proteins and nucleic acids even in unpurified samples.