Estimation of rotavirus immunoglobulin G antibodies in human serum samples by enzyme-linked immunosorbent assay: expression of results as units derived from a standard curve

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Abstract
A method for estimating rotavirus IgG antibodies by assay of human serum samples at a single serum dilution was studied. Antibody was measured by enzyme linked immunosorbent assay ELISA. The optical density of the reaction with a 1:100 dilution of each serum was expressed as ELISA units of antirotavirus IgG by reference to a standard curve. This standard curve was obtained by incorporation in each assay of 5 dilutions of a serum containing an arbitrary number of units of antirotavirus IgG. Test serum samples found to contain high amounts of antirotavirus IgG were reassayed at a 1:1000 dilution. There was good correlation between antirotavirus IgG ELISA units in 45 serum sampled and endpoint titers of the same sample (Spearman rank correlation coefficient rs, 0.95). Seroconversion during rotavirus infection was defined as an increase in antirotavirus IgG ELISA units per milliliter of > 28% (2 .times. intra-run coefficient of variation of the assay) in consecutive serum samples from the same child. Paired serum samples from 9 children with diarrhea not due to rotavirus infection showed no seroconversions. Paired samples from 8 children with rotavirus infection showed seroconversions. Estimation of antirotavirus IgG ELISA units in serum is simple, rapid, reproducible and economical of serum samples. Standardization of results could be achieved by worldwide distribution of a standard serum. Its use would facilitate epidemiological surveys to evaluate potential rotavirus vaccines.