Very high resolution single pass HLA genotyping using amplicon sequencing on the 454 next generation DNA sequencers: Comparison with Sanger sequencing.

Compared to Sanger sequencing, next-generation sequencing offers advantages for high resolution HLA genotyping including increased throughput, lower cost, and reduced genotype ambiguity. Here we describe an enhancement of the Roche 454 GS GType HLA genotyping assay to provide very high resolution (VHR) typing, by the addition of 8 primer pairs to the original 14, to genotype 11 HLA loci. These additional amplicons help resolve common and well-documented alleles and exclude commonly found null alleles in genotype ambiguity strings. Simplification of workflow to reduce the initial preparation effort using early pooling of amplicons or the Fluidigm Access Array™ is also described. Performance of the VHR assay was evaluated on 28 well characterized cell lines using Conexio Assign MPS software which uses genomic, rather than cDNA, reference sequence. Concordance was 98.4%; 1.6% had no genotype assignment. Of concordant calls, 53% were unambiguous. To further assess the assay, 59 clinical samples were genotyped and results compared to unambiguous allele assignments obtained by prior sequence-based typing supplemented with SSO and/or SSP. Concordance was 98.7% with 58.2% as unambiguous calls; 1.3% could not be assigned. Our results show that the amplicon-based VHR assay is robust and can replace current Sanger methodology. Together with software enhancements, it has the potential to provide even higher resolution HLA typing.

Novel C1q assay reveals a clinically relevant subset of human leukocyte antigen antibodies independent of immunoglobulin G strength on single antigen beads.

It has been known for 40 years that cytotoxic human leukocyte antigen (HLA) antibodies are associated with graft rejection. However, the complement-dependent cytotoxicity assay (CDC) used to define these clinically deleterious antibodies suffers from a lack of sensitivity and specificity. Recently, methods exploiting immunoglobulin G (IgG) antibody binding to HLA single antigen beads (SAB) have overcome sensitivity and specificity drawbacks but introduced a new dilemma: which of the much broader set of antibodies defined by these methods are clinically relevant. To address this, we developed a complement-fixing C1q assay on the HLA SAB that combines sensitivity, specificity, and functional potential into one assay. We compared the CDC, IgG, and C1q assays on 96 sera having 2,118 defined antibodies and determined that CDC detects only 19% of complement-fixing antibodies detected by C1q, whereas C1q detects only 47% of antibodies detected by IgG. In the same patient, there is no predictability by IgG mean fluorescence intensity (MFI) as to which of the antibodies will bind C1q because fixation is independent of MFI values. In 3 clinical studies, C1q(+) antibodies appear to be more highly correlated than those detected by IgG alone for antibody-mediated rejection in hearts as well as for kidney transplant glomerulopathy and graft failure.

A multi-site study using high-resolution HLA genotyping by next generation sequencing.

The high degree of polymorphism at human leukocyte antigen (HLA) class I and class II loci makes high-resolution HLA typing challenging. Current typing methods, including Sanger sequencing, yield ambiguous typing results because of incomplete genomic coverage and inability to set phase for HLA allele determination. The 454 Life Sciences Genome Sequencer (GS FLX) next generation sequencing system coupled with conexio atf software can provide very high-resolution HLA genotyping. High-throughput genotyping can be achieved by use of primers with multiplex identifier (MID) tags to allow pooling of the amplicons generated from different individuals prior to sequencing. We have conducted a double-blind study in which eight laboratory sites performed amplicon sequencing using GS FLX standard chemistry and genotyped the same 20 samples for HLA-A, -B, -C, DPB1, DQA1, DQB1, DRB1, DRB3, DRB4, and DRB5 (DRB3/4/5) in a single sequencing run. The average sequence read length was 250 base pairs and the average number of sequence reads per amplicon was 672, providing confidence in the allele assignments. Of the 1280 genotypes considered, assignment was possible in 95% of the cases. Failure to assign genotypes was the result of researcher procedural error or the presence of a novel allele rather than a failure of sequencing technology. Concordance with known genotypes, in cases where assignment was possible, ranged from 95.3% to 99.4% for the eight sites, with overall concordance of 97.2%. We conclude that clonal pyrosequencing using the GS FLX platform and CONEXIO ATF software allows reliable identification of HLA genotypes at high resolution.

Intravenous gammaglobulin (IVIG): a novel approach to improve transplant rates and outcomes in highly HLA-sensitized patients.

Intravenous immunoglobulin (IVIG) products are derived from pooled human plasma and have been used for the treatment of primary immunodeficiency disorders for more than 24 years. Shortly after their introduction, IVIG products were also found to be effective in the treatment of autoimmune and inflammatory disorders. Over the past 2 decades, the list of diseases where IVIG has a demonstrable beneficial effect has grown rapidly. These include Kawasaki disease, Guillain-Barre syndrome, myasthenia gravis, dermatomyositis and demyelinating polyneuropathy. Recently, we have described a beneficial effect on the reduction of anti-HLA antibodies with subsequent improvement in transplantation of highly HLA-sensitized patients as well as a potent anti-inflammatory effect that is beneficial in the treatment of antibody-mediated rejection (AMR). These advancements have enabled transplantation of patients previously considered untransplantable. These studies and relevant mechanism(s) of action will be discussed here.

Intravenous immune globulin treatment inhibits crossmatch positivity and allows for successful transplantation of incompatible organs in living-donor and cadaver recipients.

BACKGROUND: Sensitization to human leukocyte antigens (HLA) is a significant barrier to transplantation. Currently, no proven therapy exists to improve access to transplantation for highly sensitized patients. Here, we report a novel approach using intravenous immune globulin to modulate anti-HLA antibody and improve the chances for successful transplantation. PATIENTS AND METHODS: Forty-five highly HLA-sensitized patients presented as candidates for living-donor kidney transplantation (n=28), cadaveric kidney transplantation (n=15), or heart transplantation (n=2). All patients had a positive CDC crossmatch (CMX) with their donors. In living-donor recipients, intravenous immune globulin (IVIG) was added to the CMX evaluation to determine whether blocking antibodies present in IVIG could inhibit cytotoxicity. For those who showed in vitro inhibition with IVIG (n=26), IVIG was administered (usually as a single dose, 2 g/kg) and the CDC CMX was repeated against the prospective donor immediately after IVIG infusion. If negative, the patient underwent transplantation with their living-donor kidney within 24 to 72 hr. A similar but modified protocol was performed for cadaver donor candidates, all of whom were highly sensitized and had had CMX positivity with multiple donors, negating transplantation. Reductions in CMX positivity, posttransplantation serum creatinine level, number and severity of rejection episodes, and patient and graft survival rates were determined. RESULTS: Forty-two patients underwent transplantation. IVIG treatment completely abrogated the donor-specific CMXs in 35 of 42 patients. In the remaining 7 patients, the CDC CMX was inhibited, but flow cytometry CMXs remained positive. A total of 13 (31%) of 42 recipients developed rejection episodes 3 to 49 days after transplantation. Three grafts (7%) were lost to rejection. Mean serum creatinine level at 24 months was 1.4+/-0.4 mg/dL. Patient and graft survival rates were 97.6% and 89.1%, respectively, at 24 months. CONCLUSIONS: The in vitro IVIG CMX technique predicts the ability of IVIG to reduce anti-HLA antibody levels in highly sensitized patients. Subsequent in vivo IVIG treatment of responders eliminates the positive CDC CMX and allows for successful transplantation. Thus a positive CMX result is not necessarily a contraindication for transplantation and allows access to transplantation for patients for whom it was previously contraindicated.

Isolation, characterization, and transplantation of bone marrow-derived hepatocyte stem cells.

Recently it was shown that a population of cells in the bone marrow-expressing hematopoietic stem cell antigens could differentiate into hepatocytes. However, explicitly committed hepatocyte progenitors, which exhibit highly differentiated liver functions, immediately upon isolation, have not yet been isolated from bone marrow. After studying common antigens on blast-like cells in fetal and adult regenerating cholestatic rat livers and human regenerating and malignant livers, we hypothesized that beta-2-microglobulin-negative (beta(2)m(-)) cells might represent dedifferentiated hepatocytes and/or their progenitors. Utilizing a two-step magnetic bead cell-sorting procedure, we show that in bone marrow from rat and human, beta(2)m(-)/Thy-1(+) cells consistently express liver-specific genes and functions. After intraportal infusion into rat livers, bone marrow-derived hepatocyte stem cells (BDHSC) integrated with hepatic cell plates and differentiated into mature hepatocytes. In a culture system simulating liver regeneration and containing cholestatic serum, these cells differentiated into mature hepatocytes and metabolized ammonia into urea. This differentiation was dependent on a yet nondescript humoral signal existing in the cholestatic serum. Transmission electron microscopy and three-dimensional digital reconstruction confirmed hepatocyte ultrastructure of cultured BDHSC.

HLA class II haplotype associations with inflammatory bowel disease in Jewish (Ashkenazi) and non-Jewish caucasian populations.

Ulcerative colitis (UC) and Crohn's disease (CD) are the clinical entities comprising idiopathic inflammatory bowel disease (IBD). Previous studies on the association of IBD and human leukocyte antigen (HLA) class II genes suggested a role for HLA in this disease. Here we present HLA class II (DRB1, DQB1, DQA1, DPB1) allele and haplotype distributions determined using the polymerase chain reaction and sequence-specific oligonucleotide probe methods. A total of 578 UC and CD Caucasian patients and controls from Jewish (Ashkenazi) and non-Jewish populations was examined. Our previously reported association of DR1-DQ5 with CD was attributable to DRB1*0103. A dramatic association with IBD and the highly unusual DRB1*0103-DQA1*0501-DQB1*0301 haplotype (OR = 6.6, p = 0.036) was found. The more common DR1 haplotype, DRB1*0103-DQA1*0101-DQB1*0501, was also associated with IBD (OR = 3.1, p = 0.014), a result suggesting that interaction between DR and DQ may determine the extent of disease risk. Our previously reported association of DR2 with UC was attributable to DRB1*1502 (OR = 2.6, p = 0.006). At the DPB1 locus, a significant association of DPB1*0401 with CD was observed for the combined populations (OR = 1.85, p = 0.007). These observations indicate that some class II alleles and haplotypes confer susceptibility to both UC and CD, implying common immunogenetic mechanisms of pathogenesis, while others confer risk to only one of these diseases, and illustrate the value of DNA HLA typing in disease susceptibility analyses.

Linkage of Crohn's disease to the major histocompatibility complex region is detected by multiple non-parametric analyses.

BACKGROUND: There is evidence for genetic susceptibility to Crohn's disease, and a tentative association with tumour necrosis factor (TNF) and HLA class II alleles. AIMS: To examine the potential of genetic linkage between Crohn's disease and the MHC region on chromosome 6p. METHODS: TNF microsatellite markers and, for some families, additional HLA antigens were typed for 323 individuals from 49 Crohn's disease multiplex families to generate informative haplotypes. Non-parametric linkage analysis methods, including sib pair and affected relative pair methods, were used. RESULTS: Increased sharing of haplotypes was observed in affected sib pairs: 92% (48/52) shared one or two haplotypes versus an expected 75% if linkage did not exist (p=0.004). After other affected relative pairs were included, the significance level reached 0.001. The mean proportion of haplotype sharing was increased for both concordant affected (pi=0.60, p=0.002) and unaffected sib pairs (pi=0.58, p=0. 031) compared with the expected value (pi=0.5). In contrast, sharing in discordant sib pairs was significantly decreased (pi=0.42, p=0. 007). Linear regression analysis using all three types of sib pairs yielded a slope of -0.38 at p=0.00003. It seemed that the HLA effect was stronger in non-Jewish families than in Jewish families. CONCLUSIONS: All available analytical methods support linkage of Crohn's disease to the MHC region in these Crohn's disease families. This region is estimated to contribute approximately 10-33% of the total genetic risk to Crohn's disease.

Posttransplant therapy using high-dose human immunoglobulin (intravenous gammaglobulin) to control acute humoral rejection in renal and cardiac allograft recipients and potential mechanism of action.

BACKGROUND: Intravenous gammaglobulin (i.v.IG) contains anti-idiotypic antibodies that are potent inhibitors of HLA-specific alloantibodies in vitro and in vivo. In addition, highly HLA-allosensitized patients awaiting transplantation can have HLA alloantibody levels reduced dramatically by i.v.IG infusions, and subsequent transplantation can be accomplished successfully with a crossmatch-negative, histoincompatible organ. METHODS: In this study, we investigated the possible use of i.v.IG to reduce donor-specific anti-HLA alloantibodies arising after transplantation and its efficacy in treating antibody-mediated allograft rejection (AR) episodes. We present data on 10 patients with severe allograft rejection, four of whom developed AR episodes associated with high levels of donor-specific anti-HLA alloantibodies. RESULTS: Most patients showed rapid improvements in AR episodes, with resolution noted within 2-5 days after i.v.IG infusions in all patients. i.v.IG treatment also rapidly reduced donor-specific anti-HLA alloantibody levels after i.v.IG infusion. All AR episodes were reversed. Freedom from recurrent rejection episodes was seen in 9 of 10 patients, some with up to 5 years of follow-up. Results of protein G column fractionation studies from two patients suggest that the potential mechanism by which i.v.IG induces in vivo suppression is a sequence of events leading from initial inhibition due to passive transfer of IgG to eventual active induction of an IgM or IgG blocking antibody in the recipient. CONCLUSION: I.v.IG appears to be an effective therapy to control posttransplant AR episodes in heart and kidney transplant recipients, including patients who have had no success with conventional therapies. Vascular rejection episodes associated with development of donor-specific cytotoxic antibodies appears to be particularly responsive to i.v.IG therapy.

Immunomodulatory actions of intravenous immunoglobulin (IVIG): potential applications in solid organ transplant recipients.

Intravenous gammaglobulin (IVIG) products are known to have powerful immunomodulatory and anti-inflammatory functions in vitro and in vivo. In addition, IVIG has shown benefit in the treatment of many human autoimmune and inflammatory disorders. One potential mechanism of action responsible for these beneficial effects is the down-regulation of deleterious autoantibody titers through idiotypic-anti-idiotypic networks. Until recently, few data were available on the use of IVIG in the management of alloimmune disorders. In this review, we will discuss current data on the use of pooled human gammaglobulin as an agent with potential to regulate undesirable alloimmune responses and allosensitization through similar idiotypic-anti-idiotypic circuits and how this therapy could be of benefit in the management of highly sensitized patients both pre- and post-transplant. We will also discuss other potential anti-inflammatory and immunoregulatory mechanisms induced by IVIG treatment and how these may be applied to improve transplantability and outcomes in human transplantation.

Cw*1701 defines a divergent african HLA-C allelic lineage.

The complete sequence of a new HLA-C allele, Cw*1701, was determined from a South African Zulu individual. Unique features that distinguish Cw*1701 from other HLA-C alleles include multiple point substitutions and an 18 nucleotide insertion in exon 5, which encodes the transmembrane domain. In a phylogenetic analysis of HLA-C sequences, Cw*1701 forms a third, distinct allelic lineage. A comparison of the transmembrane domain of Cw*1701 with other HLA-B and -C alleles reveals that duplications and deletions have been common in the evolution of these loci. A polymerase chain reaction based typing method was used to determine the distribution of this unusual allele in human populations. In contrast to the other two lineages of HLA-C alleles, the Cw*17 lineage is found at high frequencies only in populations of African descent. In addition, the HLA-B/Cw*17 haplotype diversity is higher in Africa.

A new syndrome of Crohn's disease and pachydermoperiostosis in a family.

Few syndromic associations with Crohn's disease are described. The aim of this study was to characterize a new syndrome of Crohn's disease associated with pachydermoperiostosis in 3 brothers. Three probands, 6 siblings, both parents, 20 of 21 third-generation relatives, and 9 spousal controls were evaluated. Serological evaluation for antineutrophil cytoplasmic antibodies and human leukocyte antigens as well as genetic testing for tumor necrosis factor microsatellites, intercellular adhesion molecule 1 polymorphisms, the interleukin 1 receptor antagonist gene, and the interleukin 1 beta gene were performed. Only the 3 probands were affected and developed pachydermoperiostosis between ages 14 and 17 years. Pachydermoperiostosis preceded Crohn's ileocolitis by 6 and 20 years in two probands, excluding secondary hypertrophic osteoarthropathy. Two probands were antineutrophil cytoplasmic antibody positive vs. 1 of 27 unaffected relatives (P < 0.001, chi 2). Haplotypes for human leukocyte antigen and tumor necrosis factor microsatellites were discordant. The probands' generation was homozygous for the common allele 1 of the interleukin 1 receptor antagonist and interleukin 1 beta genes. Two probands carried a rare polymorphism of the intercellular adhesion molecule 1 gene. A new syndrome of Crohn's disease and pachydermoperiostosis associated with antineutrophil cytoplasmic antibodies is described. Inheritance is most likely autosomal recessive by pedigree. No clear association was found between this syndrome and the gene regions evaluated.

Human diversity in killer cell inhibitory receptor genes.

The presence and expression of killer inhibitory receptor (KIR) and CD94:NKG2 genes from 68 donors were analyzed using molecular typing techniques. The genes encoding CD94:NKG2 receptors were present in each person, but KIR gene possession varied. Most individuals expressed inhibitory KIR for the three well-defined HLA-B and -C ligands, but noninhibitory KIR genes were more variable. Twenty different KIR phenotypes were defined. Two groups of KIR haplotypes were distinguished and occurred at relatively even frequency. Group A KIR haplotypes consist of six genes: the main inhibitory KIR, one noninhibitory KIR, and a structurally divergent KIR. Allelic polymorphism within five KIR genes was detected. Group B comprises more noninhibitory KIR genes and contains at least one additional gene not represented in group A. The KIR locus therefore appears to be polygenic and polymorphic within the human population.

Heterogeneous phenotypes of expression of the NKB1 natural killer cell class I receptor among individuals of different human histocompatibility leukocyte antigens types appear genetically regulated, but not linked to major histocompatibililty complex haplotype.

Natural killer (NK) cells that express the NKB1 receptor are inhibited from killing target cells that possess human histocompatibility leukocyte antigen (HLA) B molecules bearing the Bw4 serological epitope. To investigate whether NKB1 expression is affected by HLA type, peripheral blood lymphocytes of 203 HLA-typed donors were examined. Most donors had a single population of NKB1+ cells, but some had two populations expressing different cell surface levels of NKB1, and others had no detectable NKB1+ cells. Among the donors expressing NKB1, both the relative abundance of NKB1+ NK cells and their level of cell surface expression varied substantially. The percentage of NKB1+ NK cells ranged from 0 to >75% (mean 14.7%), and the mean fluorescence of the positive population varied over three orders of magnitude. For each donor, the small percentage of T cells expressing NKB1 (usually <2%), had a pattern of expression mirroring that of the NK cells. NKB1 expression by NK and T cells remained stable over the 2-yr period that five donors were tested. Patterns of NKB1 expression were not associated with Bw4 or Bw6 serotype of the donor or with the presence of any individual HLA-A or -B antigens. Cells expressing NKB1 are often found in donors who do not possess an appropriate class I ligand, and can be absent in those who express Bw4+ HLA-B antigens. Family studies further suggested that the phenotype of NKB1 expression is inherited but not HLA linked. Whereas identical twins show matching patterns of NKB1 expression, HLA-identical siblings can differ in NKB1 expression, and conversely, HLA-disparate siblings can be similar. Thus NKB1 expression phenotypes are tightly regulated and extremely heterogeneous, but not correlated with HLA type.

HLA-B16 antigens: sequence of the ST-16 antigen, further definition of two B38 subtypes and evidence for convergent evolution of B*3902.

The ST-16 antigenic specificity of the HLA-B locus is defined as a B39 variant of Mexican-Americans. Nucleotide sequencing of cDNA shows the ST-16 allele (B*3905) differs from B*39011 by a single substitution that substitutes tyrosine for aspartic acid at position 74 of the mature class I heavy chain. The complete coding region sequence for the common caucasoid allele encoding the B38 antigen has been determined. This B*3801 allele differs from B*3802 at two nucleotide substitutions within the Bw4 sequence motif. B*3801 and B*3802 may have been derived independently from B*39011 by conversion events with B alleles donating distinctive Bw4 motifs. A novel allele B*39022 derived from a Colombian Indian differs from the B*39021 allele of Japanese origin at two widely separated silent substitutions. Comparison of sequences for the known B16 alleles suggest that B*39021 and B*39022 were independently derived by recombination from B*39013 and B*39011 respectively.

Intravenous immunoglobulin suppression of HLA alloantibody in highly sensitized transplant candidates and transplantation with a histoincompatible organ.

Patients awaiting solid organ transplantation who are highly sensitized to HLA antigens remain problematic in terms of finding compatible (crossmatch-negative) donors. We have used intravenous gammaglobulin (IVIG; 10% Gamimune N) to determine both its efficacy in reducing panel-reactive antibodies in vitro and the prognostic value of the in vitro testing for in vivo efficacy. In 18 patients with PRAs ranging from 40 to 100% (mean: 77%) we found a reduction in absolute PRA of 4-70% (mean decrease: 35%; percent inhibition: 4-100%; residual PRA 0-96%). In 7 cases, the residual antibody specificity could be easily determined and often appeared to include a short HLA-A2. This was independent of A2 subtype as determined by PCR-SSOP. Testing the IVIG on a panel of 21 HLA reagent alloantisera resulted in heterogeneous inhibitory patterns (7 complete, 3 partial, 8 differential, 3 none) independent of titer or specificity. In vivo administration to a 13-year-old kidney patient awaiting retransplant resulted in a PRA drop from 95% to 15% and successful retransplantation (now 11 months post-transplant). More impressively, successive in vivo administration of IVIG to a sensitized (anti-HLA-A2, A68, A69; B57, B58) heart transplant candidate resulted in successful transplantation with an A2+ histoincompatible heart. The patient experienced only one subclinical humoral rejection in the first 5 months posttransplant. Biochemical studies to determine the effective component of IVIG show that it is the IgG fraction and not soluble antigen or the minor IgM or IgA contaminants that is responsible. This suggests an antiidiotypic modulation of anti-HLA antibodies in vitro and in vivo.

Testing the importance of each residue in a HLA-B27-binding peptide using monoclonal antibodies.

When a peptide derived from histone 3.3 was incubated with mouse L cells transfected with HLA-B27, the cells became highly reactive with Ye-2, an anti-HLA-B27 mAb. The critical residues were analyzed by testing analogues in which each of the nine residues in the peptide was consecutively substituted by 19 other amino acids. The conclusions were separately verified using a different HLA-B27-positive cell line. The ability of some of these peptides to bind to HLA-B27 was also assayed by their ability to stabilize HLA-B27 in a mutant cell line which required HLA-B27-binding peptides to express HLA-B27 at 37 degrees C. These experiments showed that in P4, P5, P6, P7, P8, and P9, all 20 different amino acids could be substituted without eliminating the ability of the analogues to bind to HLA-B27. The residues which were responsible for the HLA-B27-peptide complex reacting with the Ye-2 antibody were P8 and P9. The latter might mediate its effect by altering either the surface conformation of the closely associated HLA-B27 heavy chain or the conformation of the peptide itself.

Vitamin A-enhanced cleft palate susceptibility gene maps between C4 and B144 within the H-2 complex.

Pregnant mice congenic with C57BL/10 in the region of H-2, the major histocompatibility complex on Chromosome 17 (B10.BR, B10.A, B10.A(1R), B10.A(2R), B10.A(15R), B10.A(18R), B10.OL, or crosses between them) were fed Purina Laboratory Chow or the same diet plus 400 IU of vitamin A daily from conception and given dexamethasone (80 or 160 mg/kg) intraperitoneally on the twelfth day of pregnancy. It was found that the added vitamin A increased the frequency of isolated cleft palate only in strains that had b alleles between C4 and B144. The enhancement of susceptibility to glucocorticosteroid-induced cleft palate by vitamin A appears to be a recessive trait and the locus, called Acp, maps centromeric to another corticosteroid-induced cleft palate gene (Dcp-2) that also is in the C4:B144 interval.

Distinct associations of HLA class II genes with inflammatory bowel disease.

BACKGROUND: There are relatively few studies of HLA class II association either with Crohn's disease (CD) or ulcerative colitis (UC). The few available association studies have been carried out by serological techniques, and the results from these studies are inconclusive. METHODS: The association between HLA class II genes was studied using molecular genotyping in combination with allele-specific oligonucleotide hybridization by polymerase chain reactions. RESULTS: In UC (n = 74), we observed a positive association with the HLA DR2 allele (P = 0.008) and negative associations with the DR4 (P = 0.018) and DRw6 (P = 0.028) when compared with ethnically matched controls (n = 77). No associations were observed with any DQ alleles. In contrast, in CD (n = 95) we observed a positive association with the combination of DR1 and DQw5 alleles (P = 0.021). Furthermore, stratifying DR1 and DQw5 alleles indicated that neither allele was independently associated with CD, suggesting that the association was with the haplotype rather than either of the alleles individually. A suballele of DQw5, DQB1*0501, contributed this haplotypic association (P = 0.012). CONCLUSIONS: DR and DQ molecules firmly separate UC and CD on genetic grounds, suggesting that the contribution of the HLA class II genes to the disease susceptibility is quite different for the two disorders.