Structural and functional analysis of three D/L-like class I molecules from H-2v: indications of an ancestral family of D/L genes

A physical map of the Q region of B1O.P

The murine class I MHC Q region is part of a large complex multigene family whose members have various peptide binding functions. The structure of the Q region is complex, varying extensively in the b, d, k, and q haplotypes so far examined. To better understand the structural heterogeneity, we examined the Q region of B 10.P, a strain whose immunological characteristics are distinct from other haplotypes. A total of 89 cosmids were isolated from genomic DNA. The B 10.P Q region was found to contain seven genes in a 190-kb cluster linked to DP and two additional Q genes in a separate 55-kb cluster. The gene arrangement in this haplotype was unique and did not correspond to any other haplotype; this underscores the complexity of chromosomal structure in this region. In addition to the Q region clusters, Tla region was tentatively aligned in five clusters spanning approximately 300 kb. One 37-kb M region cosmid was also identified.

Hierarchy in the assembly of HLA-B27 and HLA-Cw3 molecules in transgenic mice

Cell surface expression of human class I molecules in transgenic mice is dependent upon the available pool of beta 2-microglobulin (beta 2m) and the affinity between mouse beta 2m and human class I molecules. HLA-B27 and HLA-Cw3 transgenes can be expressed in mouse strains of the H-2 haplotypes b, f, k, and s which encode two endogenous class I genes mapping to H-2K and H-2D. The human class I genes cannot be expressed on H-2d and H-2q haplotypes which encode three endogenous class I molecules (K,D,L). This suggests that there may be only enough mouse beta 2m molecules to support three class I molecules. When both the HLA-B27 and HLA-Cw3 genes are introduced into H-2b mice, only HLA-Cw3 reaches the cell surface. This suggests that HLA-Cw3 has a higher affinity than HLA-B27 for mouse beta 2m. The possible implications of our findings regarding the assembly, transport, and expression of class I MHC molecules in vivo are discussed.