HLA-B27 transgenic mice in the context of various H-2 haplotypes were produced. A high expression of the HLA-B27 antigen was observed in mice homozygous for H-2b, H-2f, H-2s, H-2p, H-2r, and H-2k haplotypes. Mice of the H-2v haplotype expressed HLA-B27 at an intermediate level. Expression of HLA-B27 was minimal in mice of the H-2q and H-2d haplotypes. This was observed both on the B10 background and in DBA/2 or BALB/c mice. Only minimal expression of HLA-B27 could be detected in B10.PL (KuDd) or B10.RKDB (KkSkDdLb) mice, indicating that the low level of HLA-B27 expression maps to the H-2D gene or a very closely linked gene. Integration and transcription of the HLA-B27 gene does not appear to be different between high-expressing haplotypes and low-expressing haplotypes as determined by Southern and Northern blot analysis. However, expression of HLA-B27 on the cell surface correlated with the amount of HLA-B27 and beta 2M that could be immunoprecipitated with an anti-B27 antibody. Therefore, the association of the B27 heavy chain with endogenous beta 2M and subsequent expression on the cell surface are disrupted in mice with some class I H-2D genes. Possible mechanisms that might contribute to this defect in assembly, transport, and expression of class I molecules are discussed.

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