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.

Quantitation of Ina blood group antigens.

Using indirect immunoradiometric assay the mean (+/- SD) number of Ina antigenic sites per erythrocyte was estimated to be 73857 +/- 18285 in normal adults and 20142 +/- 8571 in newborn infants. Pregnant women showed temporary reduction in Ina antigens (28144 +/- 13857), which returned to normal levels, 3-6 months after delivery. Ina antigens were shown to be denatured by papain treatment of red cells, proving it to be of glycoprotein nature.

Quantitative variations in A, B, Ht1 and Ht2 antigens on erythrocytes in leukemia and lymphoma.

Using an immunoradiometric assay, A, B, Ht1 and Ht2 antigens on erythrocyte membranes were quantitated in 192 leukemia and 23 lymphoma patients. A and B antigens were reduced in 37% and 50% of leukemia cases respectively. A wide range of antigenic reduction was observed for A antigen, while B antigenic reduction was generally 16-20%. Passive absorption of Ht1 antigen from plasma onto erythrocytes was greater in leukemic compared to normal subjects. Among patients with reduced A and B antigens, 27% had increased and 37% decreased Ht2 antigens. Incidence of reduction in antigens was significantly higher (p less than 0.001) in untreated compared to treated patients.