A two-colour immunofluorescence test with a monoclonal human proinsulin antibody improves the assay for islet cell antibodies

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Abstract
The conventional indirect immunofluorescence assay for islet cell antibodies was compared with a two-colour immunofluorescent assay to detect both islet cell antibodies with fluorescein isothiocyanate-labeled rabbit anti-human IgG and pancreatic B cells with a monoclonal human proinsulin antibody and Texas red-labeled sheep anti-mouse IgG. Determinations of end-point titres showed a correlation between the new two-colour immunofluorescent assay and the conventional indirect immunofluorescent assay in 1) selected sera positive for islet cell antibodies and insulin autoantibodies rs= 0.93 (prs=0.99 (prs=0.95 (p<0.0001). No interference between the monoclonal human proinsulin antibodies and islet cell antibodies with or without insulin autoantibodies or between the two second fluorescent antibodies was detected. It is concluded that the two-colour immunofluorescence assay is advantageous since a) it is possible to mix the reagents to avoid a more time-consuming and technically complicated assay, b) the presence of B cells can be confirmed in each section to permit detection of B cell cytoplasmic antibodies and c) microscopic evaluation is easier and more accurate, particulary in islet cell antibody negative samples.