INTERNATIONAL REFERENCE-STANDARDS - ANTIBODY STANDARDS FOR THE INDIRECT ENZYME-LINKED-IMMUNOSORBENT-ASSAY

Reference standards are used to calibrate similar assay systems agains t an international reference protocol and to provide a template for th e preparation of secondary and/or working standards. Three reference s tandards are recommended for the indirect enzyme-linked immunosorbent assay: a strong positive standard, a weak positive standard and a nega tive serum standard. The negative standard should be derived from a si ngle serum or from a serum pool which exhibits typical background acti vity in the reference protocol. The strong and weak positive standards should be derived from a single serum or from a serum pool which typi fies the humoral response (antibody) to natural infection. Suitable ca ndidates for the positive reference standards should exhibit dose/resp onse curves in the mid-range of antibody activity. The strong and weak positive standards should each be prepared from a one-time dilution i n the negative standard, to yield antibody activities which are define d by specific points on the linear portion of the dose/response curve. The strong positive standard should represent an antibody activity (a bsorbance value) midway between the upper and central points and the w eak positive standard should represent an antibody activity midway bet ween the central and lower points of the linear portion of the curve. Owing to inherent differences among assay systems, antibody activities should be expressed in relative rather than in absolute terms. It is recommended that the antibody activity of the strong positive standard should denote 100% positivity The activities of the weak positive and negative standards should then be expressed as relative percentages. Every set of international reference standards should be accompanied b y an information skeet which includes, among other things, a plot of t he dose/response curve and an indication of the dilutions used to prep are the standards.