Comparison of immunofluorescence and immunoperoxidase staining for identification of rubella virus isolates

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Abstract
To explore possible advantages of immunoperoxidase (IP) staining over immunofluorescence (IF) staining for identifying rubella virus isolates, direct comparative studies were done on the same coded clinical materials using the same rubella immune rabbit serum as the primary antiserum in both systems. The rubella immune rabbit serum and conjugated anti-rabbit immune globulins could be used more dilute in the IP system than in the IF system. Both IP and IF staining detected rubella antigen in all specimens which were positive by interference. IP staining also detected low levels of rubella antigen in a few additional specimens which were originally positive for rubella virus, but which on re-testing were negative by interference and IF staining. With 2nd-cell-culture-passage material, IP and IF staining showed comparable specificity, and the few specimens which reacted nonspecifically generally did so in both systems. Cell cultures inoculated directly with [human] urine specimens showed greater nonspecificity by IP than by IF, but this activity could be abolished by pretreatment with sodium azide and peroxide; other methods tried for inactivating endogenous peroxidase activity also destroyed rubella antigen. The intensity of staining for positive specimens was comparable in the 2 systems. More antigen was demonstrable in both systems when [baby hamster kidney] BHK-21 cells were inoculated as a cell suspension and then permitted to grow into monolayers than when the same specimens were inoculated into preformed monolayers. IP staining was considered to be a highly satisfactory alternative to IF staining for identification of rubella virus isolates.