A comparison of different enzyme-antibody conjugates for enzyme-linked immunosorbent assay

Calf intestinal alkaline phosphatase (CIAP)- and horseradish peroxidase (HRP)-linked goat antibody (Ab) conjugates have been prepared by two procedures. One procedure is by glutaraldehyde coupling of the proteins; the other is by intermolecular disulfide bond formation of the appropriately modified proteins. The conjugates, specific for rabbit IgG, were tested for their effectiveness as reagents in enzyme-linked immunosorbent assays for ragweed antigen E specific rabbit antibody. The CIAP-Ab conjugate prepared by glutaraldehyde coupling and the HRP-Ab conjugate made by disulfide bond formation were equally effective reagents for immunoassay, but the HRP-Ab conjugate obtained by glutaraldehyde coupling was definitely less useful than the other two conjugates. The assay procedure utilized an antigen E coupled paper disc as the immunosorbent and it was sensitive in the range of 0.5--100 ng per test. Inhibition of the enzyme-linked immunosorbent assay was used as a sensitive technique for measuring antigenic activity of antigen E or its derivatives.