Detection and characterization of antibodies against recombinant human erythropoietin by RIPA, ELISA and neutralization assay in patients with renal anemia.

The aim of the present study was to analyze the relations between the serum anti-erythropoietin antibody (AEAb) levels and the antibodies' neutralizing activity in 20 patients with renal anemia and rhEPO-induced antibodies. AEAb levels were determined by the enzyme-linked immunosorbent assay (ELISA, double antigen-bridging) and by radioimmunoprecipitation assay (RIPA). The bone marrow neutralization test was used to determine the neutralizing activity of the antibodies. RIPA and ELISA data resulted in closely correlated measurements. The relations between AEAb levels and the neutralizing activity of the antibodies are variable as shown by follow-up and cross-sectional evaluations of the data. Serum samples with a high antibody level (>1000 ng/ml) are associated with 100% neutralizing activity, whereas serum samples with lower AEAb levels show partial neutralizing activities or have no effect. Determining the neutralizing activity might be helpful when it comes to deciding of whether or not rhEPO therapy should be continued, specifically in patients who have low antibody levels. The apparent affinity of the AEAb as defined by inhibition of the binding of rhEPO (IC(50)) did not change in the course of the disease, nor did it correlate to the AEAb levels or the neutralizing activities.