Routine HLA-B27 typing by flow cytometry: differentiation of the products of HLA-B*2702, B*2705 and B*2708.

Patient HLA-B27 typing is widely performed as an aid to the diagnosis of several diseases, particularly ankylosing spondylitis. Typing by flow cytometry, using monoclonal antibodies, has been shown to be a potentially useful alternative to classical serology on account of its speed, simplicity and economy. However, we required a flow cytometry typing procedure that would accurately differentiate HLA-B27 (Bw4) from B2708 (Bw6) and not be confounded by other HLA-B7/B27 cross-reactive group antigens. Accordingly, we evaluated the simultaneous use of two monoclonal antibody preparations, ABC-m3-FITC (anti-B27 + weak B7)/BB7.1-PE (anti-B7) and FD705-FITC (anti-B27), by testing a highly selected panel of 62 reference lymphocytes containing examples of all HLA-B7/B27 cross-reactive group antigens, including: HLA-B42, B47, B48, B73, B703, B2702, B2705 and B2708. In addition, 268 whole blood samples from routine patient requests for B27-associated disease typing were tested in parallel with HLA-B typing using the standard complement-dependent microlymphocytoxicity test. The detailed specificity of the three monoclonal antibodies was established and the products of HLA-B2702, B2705 and B*2708 were found to be readily differentiated from each other and all other HLA-B7/B27 cross-reactive HLA-B antigens.