Molecular linkage of the HLA-DR, HLA-DQ, and HLA-DO genes in yeast artificial chromosomes

A 320-kilobase artificial chromosome encoding the human HLA DR3-DQ2 MHC haplotype confers HLA restriction in transgenic mice

MHC class II haplotypes control the specificity of Th immune responses and susceptibility to many autoimmune diseases. Understanding the role of HLA class II haplotypes in immunity is hampered by the lack of animal models expressing these genes as authentic cis-haplotypes. In this study we describe transgenic expression of the autoimmune prone HLA DR3-DQ2 haplotype from a yeast artificial chromosome (YAC) containing an intact similar320-kb region from HLA DRA to DQB2. In YAC-transgenic mice HLA DR and DQ gene products were expressed on B cells, macrophages, and dendritic cells, but not on T cells indicating cell-specific regulation. Positive selection of the CD4 compartment by human class II molecules was 67% efficient in YAC-homozygous mice lacking endogenous class II molecules (Abeta(null/null)) and expressing only murine CD4. A broad range of TCR Vbeta families was used in the peripheral T cell repertoire, which was also purged of Vbeta5-, Vbeta11-, and Vbeta12-bearing T cells by endogenous mouse mammary tumor virus-encoded superantigens. Expression of the HLA DR3-DQ2 haplotype on the Abeta(null/null) background was associated with normal CD8-dependent clearance of virus from influenza-infected mice and development of CD4-dependent protection from otherwise lethal infection with Salmonella typhimurium. HLA DR- and DQ-restricted T cell responses were also elicited following immunization with known T cell determinants presented by these molecules. These findings demonstrate the potential for human MHC class II haplotypes to function efficiently in transgenic mice and should provide valuable tools for developing humanized models of MHC-associated autoimmune diseases.

The human leukocyte antigen TAP2 gene defines the centromeric limit of melanoma susceptibility on chromosome 6p

A single human leukocyte antigen (HLA) class II allele, DQB1*0301, is strongly associated with melanoma, and the HLA-DR locus provides the telomeric boundary for melanoma susceptibility in the HLA class II region of chromosome 6. However, the centromeric boundary is unknown. This study was designed to determine whether the adjacent upstream transporter associated with antigen processing (TAP) locus, TAP2, constitutes the centromeric boundary of disease susceptibility in melanoma. Molecular oligotyping of TAP2 genes was performed for 36 Caucasian patients with melanoma and for 32 Caucasian control individuals by both amplification refractory mutation system (ARMS) polymerase chain reaction (PCR) and PCR-sequence-specific oligonucleotide (SSO) typing. TAP2 allele frequencies in the melanoma patients were compared to those in non-melanoma Caucasian control populations, and to HLA-DQ allele frequencies determined by molecular oligotyping. While HLA-DQB1*0301 was more common in this group of 36 melanoma patients compared to a group of 200 controls (56 percent vs. 27 percent, Bonferoni-corrected chi-square p < = 0.01), no significant differences were observed in TAP2 allele frequencies between melanoma patients and controls. The TAP2 locus represents the centromeric boundary of disease susceptibility for melanoma in the class II region of chromosome 6p. These results support an etiologic role for HLA-DQB1*0301 in melanoma susceptibility.

Genes, genes and more genes in the human major histocompatibility complex

The human major histocompatibility complex (MHC), on the short arm of chromosome 6, represents one of the most extensively characterised regions of the human genome. This approximately 4 Mb segment of DNA contains genes encoding the polymorphic MHC class I and class II molecules which are involved in antigen presentation during an immune response. Recently the whole of the MHC has been cloned in cosmids and/or yeast artificial chromosomes (YACs) and large portions have been characterised for the presence of novel genes. Many unrelated genes, both housekeeping and tissue specific, have been identified and the gene density in some regions is now approaching one gene every few kilobases. Some of the novel genes encode proteins involved in the intracellular processing and transport of antigens that are presented by MHC class I molecules. Others, however, have no obvious role in the immune response. The MHC is located in the chromosome band 6p21.3 which is a Giemsa (G)-light band. The detection of such a large number of functional genes (at least 70) in this region is compatible with the idea that both housekeeping and tissue-specific genes are localised predominantly in G-light bands.

Rapid identification of overlapping YACs in the MEN2 region of human chromosome 10 by hybridization with Alu element-mediated PCR products

An overlapping set of 21 yeast artificial chromosomes (YACs) spanning the RET proto-oncogene [Takahashi et al., Oncogene 3 (1988) 571-578] and D10S102 markers on human chromosome 10 was isolated in a series of hybridization-based chromosomal walks in a YAC library. Genetic linkage analyses implicate this chromosomal region as the location of the gene (MEN2A) responsible for multiple endocrine neoplasia type 2A. Four YACs carrying a RET sequence-tagged site (STS) and two YACs carrying a D10S102 STS were used to initiate chromosome walks. These were based on hybridization of Alu element-mediated polymerase chain reaction (Alu-PCR) products from YACs to dot blots of Alu-PCR products from complex pools of YAC clones. The hybridization anchor content of YACs identified in the walks was confirmed by probing blots of Alu-PCR products from individual YACs and by comparing Alu-PCR fingerprints of each YAC. Ten hybridization-based Alu-PCR anchors and three STS anchors were ordered within eleven intervals created by the 21 overlapping YACs. The order of anchors requiring the fewest gaps in the YACs is consistent with the walking results and establishes the STS anchor order as D10S102-D10S94-RET. The overlapping set of YACs represents about 1.55 Mb of the human genome according to restriction mapping of four representative YACs in the contig. These results demonstrate the power of Alu-PCR hybridization for chromosomal walking and provide a rich source of overlapping YACs which can be used to identify candidate MEN2A genes.

Identification in the HLA class I region of a gene expressed late in keratinocyte differentiation

A gene designated S has been identified in the class I region of the human major histocompatibility complex. The S gene is located 160 kb telomeric of HLA-C. It is expressed at high levels as 2.2-kb and 2.6-kb mRNAs in human skin. No homologous transcripts were detected in other tissues including placenta, liver, spleen, thymus, and brain. In situ hybridization showed that S gene expression was restricted to the differentiating keratinocytes in the granular layer of the epidermis. The predicted amino acid sequence of the S protein was remarkable for its high content of serine, glycine, and proline. There were significant similarities with the amino acid sequences of loricrin, keratin 1, and keratin 10, all major components of the granular-cell layer. The selective expression of the S gene in the granular-cell layer in the epidermis suggests a role in the developmental program of differentiating keratinocytes. Furthermore, in light of the recognized association of psoriasis vulgaris, a disorder of keratinocyte proliferation, with alleles of HLA-C, this gene may contribute primarily to the pathogenesis of this common disorder.