HLA–B27 is capable of forming in vitro a heavy-chain homodimer structure lacking β2-microglobulin. We undertook this study to ascertain if patients with spondylarthritis express β2-microglobulin–free HLA–B27 heavy chains in the form of homodimers and receptors for HLA–B27 homodimers.
Expression of HLA–B27 heavy chains by mononuclear cells was analyzed by fluorescence-activated cell sorter staining, Western blotting with the monoclonal antibody HC-10, and 2-dimensional isoelectric focusing. Fluorescence-labeled tetrameric complexes of HLA–B27 heavy-chain homodimers were constructed in which each dimer comprised one His-tagged heavy chain and one biotinylated heavy chain, and were used to stain patient and control mononuclear cells and transfected cell lines.
Patients with spondylarthritis expressed cell-surface HLA–B27 homodimers. Populations of synovial and peripheral blood monocytes, and B and T lymphocytes from patients with spondylarthritis, and controls carried receptors for HLA–B27 homodimers. Experiments with transfected cell lines demonstrated that KIR3DL1 and KIR3DL2, and immunoglobulin-like transcript 4 (ILT4), but not ILT2, are receptors for HLA–B27 homodimers.
Patients with spondylarthritis express both HLA–B27 heavy-chain homodimers and receptors for HLA–B27 homodimers. This may be of significance with regard to disease pathogenesis.