SEROLOGICAL DIAGNOSIS OF MUMPS AND PARAINFLUENZA TYPE‐1 VIRUS INFECTIONS BY ENZYME IMMUNOASSAY, WITH A COMPARISON OF TWO DIFFERENT APPROACHES FOR DETECTION OF MUMPS IgG ANTIBODIES

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Abstract
Two solid-phase enzyme-linked immunosorbent assays (ELISA) for detection of mumps IgG antibodies, viz., indirect ELISA and catching-antibodies (C.A.)-ELISA, are described and the results obtained with both assays are compared with each other and with the conventional complement-fixation (CF) test. In the indirect method, mumps antigens are used for coating the wells of the microtest plates, whereas in the C.A.-ELISA method mumps antigens are selectively bound to rabbit anti-mumps antibodies coated surfaces. A positive correlation was found between the optical density (O.D.) values given by both ELISA assays and CF-antibody titers. The ELISA assays showed improved sensitivity compared to the CF test, since 54% (C.A.-ELISA) and 33% (Indirect-ELISA) of additional positive reactions were detected by these assays. In terms of specificity, however, only the C.A.-ELISA was superior to CF, since significant rises of IgG-antibodies were detected only in paired sera of mumps patients. Conversely, when the indirect method was used significant IgG antibody rises were demonstrated in paired sera from mumps patients and in serum pairs of six patients with parainfluenza type-1 virus infection. With the CF test, heterologous antibodies responses were demonstrated in 2 of these patients. Absorption experiments of mumps sera with mumps and parainfluenza virus strains demonstrated that the IgG antibodies detected by the C.A.-ELISA are specific for mumps virus and therefore interference due to heterologous antibody responses were not observed. Results with purified mumps virus proteins demonstrated that the antigen-antibody reactions that partake in the C.A.-ELISA are mainly associated with the nucleoprotein antigen. Detection of IgG-antibodies to parainfluenza virus type-1 was assessed by ELISA (paraflu-T1-ELISA) using only the indirect approach. The results obtained with this assay showed improved sensitivity compared to a paraflu Tl-CF test, since 47% of additional positive reactions were demonstrated by ELISA. In terms of specificity, however, heterologous antibody responses were detected by both the ELISA and the CF test in 4 out of 20 patients with mumps infections.