Expression of HLA‐B27 in transgenic mice is controlled by the H‐2D gene(s)

The HLA‐B27 transgene was introduced into mice of the B10 background with various H‐2 haplotypes. High levels of B27 antigen were detected on the surface of peripheral‐blood lymphocytes from mice homozygous for the H‐2^b, H‐2^f, H‐2^s, H‐2^P, H‐2^r and H‐2^k haplotypes. In contrast, cell‐surface expression of B27 was decreased in mice homozygous for the H‐2^d, H‐2^q and H‐2^v haplotypes. Only minimal levels of B27 could be detected on cells from B10.RKDB (K^kS^kD^dL^b) mice, indicating that the H‐2D region of the H‐2^d haplotype appears to interfere with B27 expression. To try to determine the specific area of the H‐2D genes affecting B27 expression, the B27 transgene was introduced into B10.D2‐dml and BALB/c‐dm2 mice. Expression was normal in the dm2 animals which have only one functional gene, D^d, in the H‐2D region. High levels of B27 expression were observed in the dm I animals. These mice also have only one functional H‐2D gene, but it is a hybrid gene formed by the fusion of the 5′ part of the D^d gene and the 3′ part of the L^d gene. Thus, low expression of B27 is controlled by gene(s) mapping between H‐2D and H‐2L.