The complex interplay of the DQB1 and DQA1 loci in the generation of the susceptible and protective phenotype for insulin-dependent diabetes mellitus

Typing of a polymorphic human gene conferring susceptibility to insulin-dependent diabetes mellitus by picosecond-resolved FRET on non-purified/non-amplified genomic DNA

This work concerns the identification of the alleles of the polymorphic DQB1 gene of the human leukocyte antigen system, conferring susceptibility to the development of insulin-dependent diabetes mellitus (IDDM) in non-PCR amplified DNA samples and, more importantly, in crude cell extracts. Our method is based on the time-resolved analysis of a Förster energy-transfer mechanism that occurs in a dual-labelled fluorescent probe specific for the IDDM-associated DQB1-0201 allele. Such an oligonucleotide probe is labelled, at the two ends, by a pair of chromophores that operate as donor and acceptor in a Förster resonant energy transfer. The donor fluorescence is quenched with an efficiency that is strongly dependent on the donor-to-acceptor distance, hence on the configuration of the probe after hybridization with the various DQB1 alleles. By time-correlated single-photon counting, performed with an excitation/detection system endowed with 30-ps resolution, we measure the time-resolved fluorescence decay of the donor and discriminate, by means of the decay–time value, the DNA bearing the ‘susceptible’ allele from the DNAs bearing any other sequence in the same region of the DQB1 gene. We could also distinguish the presence of the DQB1-0201 allele in a homozygous versus a heterozygous condition.

Time-resolved FRET method for typing polymorphic alleles of the human leukocyte antigen system by using a single DNA probe

By tens-of-picosecond resolved fluorescence detection we study Förster resonance energy transfer between a donor and a black-hole-quencher acceptor bound at the 5'- and 3'-positions of a probe-oligonucleotide matching an allelic region of a class II antigen of the human leukocyte antigen system, namely the region between codons 52 and 57 of the HLA DQB1 0201 allele. This dual-labelled probe is annealed with either the exactly complementary allelic sequence or with polymorphic sequences of the same region. We detect the longest-lived donor fluorescence in the case of the perfect hybridization achieved with the 0201 allele and definitely faster and distinct decays for the other allelic variants, some of which are single-nucleotide polymorphic variants.

Specificity of peptide selection by antigen-presenting cells homozygous or heterozygous for expression of class II MHC molecules: The lack of competition

We isolated and identified naturally processed peptides selected by antigen-presenting cells homozygous for expression of I-A(g7) or I-A(d) class II MHC molecules, or from heterozygous antigen-presenting cells that express I-A(g7) along with I-A(g7PD) or I-A(d). Identification of large numbers of peptides demonstrated that despite being closely related on a structural level, each class II MHC molecule selected for very unique peptides. The large data sets allowed us to definitively establish the preferred peptide-binding motifs critical for selection of peptides by I-A(g7), I-A(g7PD), and I-A(d). Finally, extensive analyses of peptide families reveals that there was little competition among class II MHC alleles for display of peptides and that presence of one allele had minimal impact on the repertoire of peptides selected by another.

The regulatory role of DR4 in a spontaneous diabetes DQ8 transgenic model

MHC class II molecules are critical determinants of genetic susceptibility to human type 1 diabetes. In patients, the most common haplotype contains the DRA1*0101-DRB1*0401 (DR4) and DQA1*0301-DQB1*0302 (DQ8) loci. To assess directly the relative roles of HLA-DQ8 and DR4 for diabetes development in vivo, we generated C57BL/6 transgenic mice that lack endogenous mouse MHC class II molecules but express HLA-DQ8 and/or DR4. Neither HLA-DQ nor HLA-DR transgenic mice developed insulitis or spontaneous diabetes. However, when they were crossed to transgenic mice (C57BL/6) expressing the B7.1 costimulatory molecules on pancreatic beta cells that do not normally develop diabetes, T cells from these double transgenic mice were no longer tolerant to islet autoantigens. The majority of DQ8/RIP-B7 mice developed spontaneous diabetes, whereas only 25% of DR4/RIP-B7 mice did so. Interestingly, when DQ8 and DR4 were coexpressed (DQ8DR4/RIP-B7), only 23% of these mice developed diabetes, an incidence indistinguishable from the DR4/RIP-B7 mice. T cells from both DR4/RIP-B7 and DQ8DR4/RIP-B7 mice, unlike those from DQ8/RIP-B7 mice, exhibited a Th2-like phenotype. Thus, the expression of DR4 appeared to downregulate DQ8-restricted autoreactive T cells in DQ8DR4/RIP-B7 mice. Our data suggest that although both DQ8 and DR4 can promote spontaneous diabetes in mice with a non-autoimmune-prone genetic background, the diabetogenic effect of the DQ8 allele is much greater, whereas DR4 expression downregulates the diabetogenic effect of DQ8, perhaps by enhancing Th2-like immune responses.

Analysis of CIITA encoding AIR-1 gene promoters in insulin-dependent diabetes mellitus and rheumatoid arthritis patients from the northeast of Italy: absence of sequence variability

Qualitative and/or quantitative alterations in the expression of the MHC class II molecules affect the onset and maintenance of the immune response and may be the basis of a wide variety of disease states, such as autoimmunity and immunodeficiency.CIITA is a major physiological regulator of the expression of MHC class II genes. The availability of CIITA ap- pears generally essential for MHC class II gene expression, and hence its own transcriptional regulatory mechanisms result of fundamental importance for a correct homeostasis of the immune response. Therefore, it is possible to hypothesize that variability at the CIITA-encoding locus, AIR-1, could constitute an additional source of susceptible traits to autoimmune diseases. Mutations at AIR-1/CIITA promoters could modulate expression of CIITA. Variations in CIITA expression could influence the qualitative and quantitative expression of MHC class II molecules at cell surface. We have analyzed sequence variation at AIR-1/CIITA promoters by PCR-SSCP in 23 IDDM and 30 RA patients compared to a sample of 19 unaffected normal controls and 16 unaffected IDDM family members, for a total of 88 Caucasian subjects from the Northeast of Italy. No sequence difference was found at the four AIR-1/CIITA promoters between autoimmune patients and normal controls. Moreover, the promoters resulted invariant within the entire group of 88 subjects analyzed, comprising patients and controls. This finding suggests a possible selective advantage in maintaining CIITA upstream regulatory sequences invariant.

NOD background genes influence T cell responses to GAD 65 in HLA-DQ8 transgenic mice

The major histocompatibility complex (MHC) genes play a significant role in the predisposition to insulin-dependent diabetes mellitus or type 1 diabetes. HLA-DQ8 (DQB1*0302, DQA 1*0301) genes have been shown to have the highest relative risk for human type 1 diabetes. To develop a "humanized" mouse model of diabetes, HLA-DQ8 was transgenically expressed in mice lacking endogenous class II genes. Since non-MHC background genes of the NOD influence the disease process, AP"/DQ8 mice were mated with the NOD strain and backcrossed to generate Abeta degree/DQ8/NOD mice. These mice have DQ8 as the sole MHC class II restriction element with NOD background genes at the N 2 generation. The DQ8 transgenic mice were used to identify T cell epitopes on glutamic acid decarboxylase (GAD 65), an important putative autoantigen in type 1 diabetes. The NOD background genes strongly influenced antigen processing, that is, different T cell epitopes were generated from the processing of GAD 65 in vivo in the Abeta degree/DQ8 and in the Abeta degree/DQ8/NOD mice.

HLA-DQ6/8 Double Transgenic Mice Develop Auricular Chondritis Following Type II Collagen Immunization: A Model for Human Relapsing Polychondritis

We have generated transgenic (tg) mice expressing HLA-DQ8αβ (DQA1*0301/DQB*0302) or HLA-DQ6αβ (DQA1*0103/DQB1*0601) molecules lacking endogenous murine class II expression (Aβ0) to investigate the ability of these HLA class II to present type II collagen (CII) and induce collagen-induced arthritis. The DQ8αβ tg mice responded strongly to CII, developing severe arthritis, while DQ6αβ tg mice were nonresponsive to CII. The addition of the mixed haplotype DQ8α6β molecule did not significantly influence CII reactivity. To examine the interaction of DQ6αβ and DQ8αβ molecules in vivo, we generated double tg DQ6αβ/8αβ (Aβ0) mice expressing both the α- and β-chains of DQ6 and DQ8 molecules by mating DQ6αβ (Aβ0) and DQ8αβ (Aβ0) tg mice. CII-immunized DQ6αβ/8αβ tg mice developed severe experimental polychondritis, exhibiting both polyarthritis and auricular chondritis. The clinical, serologic, and histologic manifestations of experimental polychondritis are similar to those symptoms in human relapsing polychondritis. The susceptibility of DQ6αβ/8αβ tg mice compared with resistance in the parental strains suggests that expression of both the DQ6αβ and DQ8αβ tgs, unique to the DQ6αβ8αβ tg strain, is important in susceptibility to experimental polychondritis. The DQ6αβ/8αβ tg mice provide a model to investigate putative autoantigens and the mechanisms of pathogenesis involved in relapsing polychondritis as well as the influence of the expression of multiple HLA class II molecules on the disease process.

Induction of insulitis by glutamic acid decarboxylase peptide-specific and HLA-DQ8-restricted CD4(+) T cells from human DQ transgenic mice

Insulin-dependent diabetes mellitus in humans is linked with specific HLA class II genes, e.g., HLA-DQA1*0301/ DQB1*0302 (DQ8). To investigate the roles of HLA-DQ8 molecules and glutamic acid decarboxylase (GAD) in disease development, we generated DQ8(+)/I-Abo transgenic mice expressing functional HLA-DQ8 molecules and devoid of endogenous mouse class II. DQ8(+)/I-Abo mice produced antigen-specific antibodies and formed germinal centers after immunization with GAD65 peptides. Two GAD peptide-specific (247-266 and 509-528), DQ8 restricted Th1 CD4(+) T cell lines, were generated from immunized DQ8(+)/I-Abo mice. They induced severe insulitis after adoptive transfer into transgene positive (but not negative) mice who were treated with a very low dose of streptozotocin that alone caused no apparent islet pathology. In addition to CD4, islet mRNA from these mice also showed expression of CD8, IFNgamma, TNFalpha, Fas, and Fas ligand. Our data suggest that a mild islet insult in the presence of HLA-DQ8 bearing antigen-presenting cells promotes infiltration of GAD peptide reactive T cells into the islet.

Evidence that an HLA-DQA1-DQB1 haplotype influences susceptibility to childhood common acute lymphoblastic leukaemia in boys provides further support for an infection-related aetiology

Comparison of DQA1 and DQB1 alleles in 60 children with common acute lymphoblastic leukaemia (c-ALL) and 78 newborn infant control subjects revealed that male but not female patients had a higher frequency of DQA1*0101/*0104 and DQB1*0501 than appropriate control subjects. The results suggest a male-associated susceptibility haplotype in c-ALL and supports an infectious aetiology.

Molecular analysis of HLA-DQB1 alleles in childhood common acute lymphoblastic leukaemia

Epidemiological studies suggest that childhood common acute lymphoblastic leukaemia (c-ALL) may be the rare outcome of early post-natal infection with a common infectious agent. One of the factors that may determine whether a child succumbs to c-ALL is how it responds to the candidate infection. Since immune responses to infection are under the partial control of (human leucocyte antigen) HLA genes, an association between an HLA allele and c-ALL could provide support for an infectious aetiology. To define the limit of c-ALL susceptibility within the HLA region, we have compared HLA-DQB1 allele frequencies in a cohort of 62 children with c-ALL with 76 newborn controls, using group-specific polymerase chain reaction (PCR) amplification, and single-strand conformation polymorphism (SSCP) analysis. We find that a significant excess of children with c-ALL type for DQB1*05 [relative risk (RR): 2.54, uncorrected P=0.038], and a marginal excess with DQB1*0501 (RR: 2.18; P=0.095). Only 3 of the 62 children with c-ALL have the other susceptibility allele, DPB1*0201 as well as DQB1*0501, whereas 15 had one or the other allele. This suggests that HLA-associated susceptibility may be determined independently by at least two loci, and is not due to linkage disequilibrium. The combined relative risk of the two groups of children with DPB1*0201 and/or DQB1*0501 is 2.76 (P=0.0076). Analysis of amino acids encoded by exon 2 of DQB1 reveal additional complexity, with significant (P<0.05) or borderline-significant increases in Gly26, His30, Val57, Glu66-Val67 encoding motifs in c-ALL compared with controls. Since these amino acids are not restricted to DQB1*0501, our results suggest that, as with DPB1, the increased risk of c-ALL associated with DQB1 is determined by specific amino acid encoding motifs rather than by an individual allele. These results also suggest that HLA-associated susceptibility to c-ALL may not be restricted to the region bounded by DPB1 and DQB1.

Genetics of autoimmune disease

In the past year, the major advances in understanding the genetics of autoimmune disease in both man and mouse have been made as a result of using the positional cloning approach. Construction of congenic mouse strains, and, in humans, the exploitation of linkage disequilibrium between very closely linked markers and disease-predisposing loci, is enabling fine mapping of these loci.