Evaluation of a modified IRMA for anti-D quantitation, using 3H protein A.

A modified immunoradiometry assay (IRMA) using tritiated (3H) protein A was developed to estimate anti-D concentration. The main advantages of the assay were longer shelf life of the labelled reagent (more than two years); minimum radiation hazard and; low non specific binding. Levels of anti-D were estimated in 23 Rh (D) immunised women. A good correlation of anti-D concentration (micrograms/ml) with Rh antibody titre was observed (r = +0.89, P < 0.01). Anti-D concentration estimated by 3H protein A IRMA correlated well with the severity of Rh-HDN. This assay could quantitate anti-D in sera having exclusively IgG3 subtype.

Protein A-antibody mediated hemagglutination assay for serodiagnosis of amebic liver abscess.

A successful modification of the indirect hemagglutination test to demonstrate antibodies for serodiagnosis of amebic liver abscess has been described in the present study. In the modified test, the protein A-IMA, Staphylococcus aureus (Cowan's strain I) bearing protein A (SAPA) cells were used to enhance hemagglutination of sensitized red cells. Use of SAPA cells markedly enhanced sensitivity of the test and greatly increased the titers obtained with most of the sera. At a diagnostic antibody titer of 1:128 and above, the protein A-IHA could detect 72 (100%) of amebic liver abscess (ALA) cases. Amongst the controls, no false positive reaction was observed in non-amebic liver disease controls. However 1(2%) of sera demonstrated false positive reactions from healthy controls. The protein A-IHA was highly sensitive when compared with that of the indirect hemagglutination (IHA) for serodiagnosis of amebic liver abscess. The novel immunoassay is simple, inexpensive and requires little technical skill. It has the potential for wide application in serodiagnosis of amebic liver abscess.