ELISA for IgM and IgG antibodies against tick-borne encephalitis virus: quantification and standardization of results

A method for standardizing specific antibody determination by ELISA is presented. Tick-borne encephalitis (TBE)-ELISA results are expressed in arbitrary units by comparing extinction values of test sera (tested in triplicate at a fixed dilution) with the extinction-curve of a standard serum run in the same test. The standard serum was given an arbitrary value of 1000 Vienna Units, and the corresponding units for the test serum are read from the standard curve. As a standard for IgM antibody determination, a pool of sera was taken from patients with recent TBE at about the time of maximal IgM antibody production. This IgM-standard was used for a three-layer as well as for a four-layer ELISA. The IgG standard for detection of IgG antibodies in the three-layer ELISA consisted of sera from persons with a past infection. To exclude low nonspecific results only values higher then 50 Vienna Units are regarded as undoubtedly positive. This method for standardizing ELISA gives reproducible results, even when plates coated on different days with different batches of antigen were used.