Detection of antibody isotypes to streptolysin O by dot ELISA

The presence of antibody isotypes (IgG, IgA and IgM) to streptolysin O was determined by dot ELISA in 222 serum samples from patients with different levels of anti-streptolysin O (SLO) antibodies as measured by the neutralizing assay (NA), from patients with diseases not related to nonsuppurative complications of Streptococcus pyogenes infection, and from clinically healthy individuals. Immunoglobulin G antibodies were found in 72 per cent of sera from patients with SLO antibodies higher than 333 Todd units (TU), and IgA antibodies were also detected in 53 per cent, but no IgM antibodies were demonstrable. High copositivity (0.94), conegativity (0.97), and positive (0.96) and negative (0.96) predictive values were observed when IgG and IgA findings were combined. The dot ELISA gave highly reproducible results. The present data suggest that the assay may be of practical value for routine detection of SLO antibodies when employed with an anti-human immunoglobulin light chain peroxidase conjugate.

Diffusion-in-gel enzyme-linked immunosorbent assay (DIG-ELISA) for Chagas'disease serodiagnosis

Diffusion-in-gel enzyme-linked immunosorbent assay (DIG-ELISA) was standardized and evaluated for the diagnosis of Chagas'disease in comparison with the conventional serological tests indirect immunofluorescence (IFI), passive hemagglutination (PHA) and complement fixation (CF). A total of 236 serum samples positive and negative for the serodiagnosis of Chagas'disease were studied. The group included 50 serum samples serologically positive for leishmaniasis and 36 positive for malaria. The best diagnostic performance of DIG-ELISA was observed when serum samples were diluted to 1:8 and a diameter of zero mm (no color) was taken as the cut-off. Under these conditions, the relative indices of sensitivity, specificity and agreement were 100%. High positive correlation coeficients were obtained between DIG-ELISA and IFI (r1=0.9010), PHA (r2=0.8943) and CF (r3=0.8269). We conclude that DIG-ELISA provides an alternative technique for screening chagasic infections, as well as for seroepidemiological surveys mainly because it is simple, easy to carry out and does not require expensive equipment