LAUSR

Aim HLA-B27 (associated with ankylosing spondylitis, juvenile rheumatoid arthritis, and Reiter’s syndrome) can be detected utilizing monoclonal antibodies. This assay is a simple qualitative two-color direct immunofluorescence flow cytometric method for rapid detection of the cell-surface glycoprotein expressed on nucleated human cells in whole blood without additional processing. This assay is known to cross-react with other HLA-B antigens, as reported with limited sampling, which yields a gray zone result. We present our observations of this cross-reactivity over approximately an eight and a half year period. Methods Whole blood samples (ACD) are tested with the BD (BD Biosciences, San Jose CA) HLA B27 kit utilizing monoclonal antibody GS145.2. Flow cytometric results falling in the gray zone were confirmed using SSO typing assay. Gray zone results were analyzed to identify cross reacting HLA-B antigens. Results In our laboratory, 311 samples fell into our defined gray zone. Analysis of this demonstrated 30 HLA-B27 cross-reactive antigens, including published HLA-B27 cross-reactive antigens and additional antigens not previously published. The 11 most common cross reactive HLA-B antigens in descending order of frequency are: HLA-B7, 44, 39, 8, 60, 51, 37, 35, 62, 18, and 64. Conclusions Our study expands on the previously published breadth of known HLA-B27 cross reactive antigens. An ongoing understanding & confirmation of gray zone results are important for accurate patient diagnosis.