Identification of previously unrecognized predisposing factors for ankylosing spondylitis from analysis of HLA-B27 extended haplotypes in Sardinia

OBJECTIVE: To define the contribution of HLA genes other than HLA-B27 in conferring susceptibility to ankylosing spondylitis (AS), through analysis of HLA-B27 haplotypes in Sardinian subjects. METHODS: Ninety-eight patients with AS, 133 HLA-B27-positive controls (of whom 33 were positive for HLA-B*2709), and 190 randomly selected controls were genotyped for microsatellites and single-nucleotide polymorphisms (SNPs) spanning the HLA region. RESULTS: Haplotypes carrying either the B*2705 or the B*2709 allele were found to share a conserved region downstream of the HLA-B gene and a functional polymorphism in the HLA-E gene (R128G), while differing in all other markers. Notably, the presence of an A at SNP rs1264457, encoding for Arg-128, was significantly increased in the cohort of patients (P = 6 x 10(-6), corrected P = 3 x 10(-5)) but not in B*2705- or B*2709-positive controls. Comparing the alleles co-occurring at each HLA marker, we identified a region differentiating patients with AS and B*2705-matched controls. In particular, there was a markedly increased prevalence of heterozygosity at rs1264457 among B27-positive controls (74%, versus 47% in patients and 54% in random controls), suggesting a protective role of G128 in AS. Moreover, other markers around the HLA-B gene were also differentially represented. CONCLUSION: These results demonstrate a significant difference in the frequency of some HLA markers between AS patients and B*2705-positive controls, which could be attributed to the opposite chromosome. In particular, the differential distribution of a functional polymorphism in the HLA-E gene suggests a possible role of natural killer function in AS pathogenesis.     

MICA gene triplet repeat polymorphism in patients with HLA-B27 positive and negative ankylosing spondylitis from Sardinia

OBJECTIVE: We investigated the distribution of MICA triplet repeat polymorphism in a random population and in patients with seronegative spondyloarthritis from Sardinia compared to continental Italy. METHODS: We analyzed the distribution of MICA triplet repeat polymorphism in HLA-B*2709 [not associated with ankylosing spondylitis (AS)] and B*2705 (associated with AS) haplotypes, to verify whether the strong association of MICA-A4 with HLA-B27 reported in other populations is maintained in Sardinia, and compared the distribution of MICA-A alleles in HLA-B27 negative versus HLA-B27+ patients with AS. RESULTS: We found that the frequency of MICA-A4 triplet repeat allele in a random Sardinia population is higher (53.2%) than in other Caucasian populations (around 20%); this allele is strongly associated with both HLA-B*2709 and B*2705. No significant difference between HLA-B27+ patients with AS and healthy controls was found: the MICA-A4 allele was present in more than 90% of subjects. MICA-A4 was found in 16 out of 20 HLA-B27 negative Sardinian patients with AS, with a frequency (80%) more similar to that of the HLA-B27+ group of patients than that of controls. CONCLUSION: The high frequency of MICA-A4 allele in HLA-B27 negative patients with AS from Sardinia, suggests the presence within the HLA region of a susceptibility factor other and certainly weaker than B27. This factor is likely to be more easily found by analyzing genetically homogeneous populations like the Sardinian, characterized by a small number of very frequent haplotypes.     

A strong association between null alleles at the C4A locus in the major histocompatibility complex and systemic sclerosis

Allotyping of the major histocompatibility complex (MHC)-linked complement component C4 has revealed a strong association of the null allele, C4A*Q0, with systemic sclerosis (SSc). Sixty-four percent of patients with SSc carried the C4A*Q0 allele, compared with 17% of the control group. Twenty-five patients and their families were typed for HLA antigens (A, B, Cw, and DR) and the MHC-linked complement components C4 and factor B to identify haplotypes in the MHC linkage group and C4 null alleles. Strong allelic association of HLA-B8 and DR3 with C4A*Q0 probably explains the previously reported association of SSc with the extended haplotype carrying HLA-B8 and DR3. Ninety-two percent of the patients had either C4A*Q0 or DR5; 31% of the controls had either C4A*Q0 or DR5.     

Distribution of HLA-B27 and its alleles in patients with reactive arthritis and with ankylosing spondylitis in Tunisia

The purpose of the present study is to investigate the frequency of HLA-B27 and its alleles in reactive arthritis (ReA) and in ankylosing spondylitis (AS) in Tunisia. HLA-B27 alleles were typed by PCR amplification with sequence-specific primers. We studied 17 patients with ReA associated with urethritis or with gastrointestinal infection; 42 HLA-B27-positive patients with AS and 100 healthy controls. Eleven ReA patients (67.7%) were HLA-B27 positive. There was an increased frequencies of HLA-B27 (P = 7.76 × 10⁻¹², OR = 59.30) and a moderate increase of HLA-B51 (P = 0.015; OR = 4.91) alleles in ReA patients when compared with healthy controls. Four B27 subtypes were identified: B*2702, 05, 09 and B*2712. The distribution of these alleles in the ReA patients was 37.5% for B*2702 and B*2705. Only these two subtypes were detected in 18 (42.8%) and 24 (57.1%), respectively, of the AS patients. B*2709 and B*2712 were relatively rare in ReA patients and were identified in one case each. Our results showed a restricted number of HLA-B27 subtypes associated with ReA and AS. B*2702 and 2705 were common in ReA and AS patients.     

Association of ankylosing spondylitis with HLA-B*1403 in a West African population

OBJECTIVE: To investigate the contribution of HLA class I alleles in the susceptibility to primary ankylosing spondylitis (AS) in West African patients living in Togo. METHODS: A large epidemiologic analysis of 9,065 West African rheumatology patients living in Togo was performed in order to identify those who had AS. Eight Togolese patients with AS were identified. HLA was typed by polymerase chain reaction using sequence-specific oligonucleotide probes. DNA typing was also performed on a control population of 85 healthy subjects matched for ethnic background. RESULTS: A significant association between AS and B*14 was identified. This allele was found in 62.5% of the AS patients (odds ratio 69), but was carried by only 2% of the healthy controls. Analysis for B14 subtypes showed that B*1403 was the predominant allele in AS patients (odds ratio 171), and that this allele was absent in healthy controls. B27 was virtually absent, being observed in only 1 AS patient (B*2705). CONCLUSION: HLA-B*1403 shows the B27 "supertype" motif and may exert an effect on AS susceptibility according to the arthritogenic peptide model. The association of B*1403 with AS has not previously been reported in either population.     

Etiopathogenic role of HLA‐B27 alleles in ankylosing spondylitis

HLA‐B27 is the major genetic susceptibility factor for ankylosing spondylitis (AS). However, its precise role in the pathogenesis of AS still remains unclear, even though its gene has been cloned and sequenced, and its crystallographic structure has been defined. Arthritogenic peptide and molecular mimicry hypotheses propose mechanisms related to an antigen‐presenting function of HLA‐B27 to be responsible for disease development. However, peculiar aspects of its immunobiology, such as its misfolding and heavy chain dimerization raise the possibility of involvement of pathogenic mechanisms unrelated to its physiological function. Moreover, HLA‐B27 is not a single allele, but a family of 31 different alleles, named HLA‐B*2701 to HLA‐B*2727. Studies worldwide indicate that the relatively common alleles (subtypes) HLA‐B*2705, B*2704, and B*2702 are strongly associated with AS, whereas HLA‐B*2706 which is prevalent in South‐east Asia and HLA‐B*2709 which is prevalent on the Italian island of Sardinia, seem to lack such an association. The distinction between the disease‐associated subtypes and those that are not associated, may provide clues to the actual role of HLA‐B27 in disease pathogenesis. B*2706 differs from B*2704 by only two residues, and B*2709 differs from B*2705 by only one residue. Moreover, both B*2706 and B*2709 bind an endogenous peptide (derived from vasoactive intestinal peptide type 1 receptor) and also an exogenous peptide (latent membrane protein 2 of Epstein‐Barr virus) but in two drastically diverse conformations. These recent X‐ray diffraction studies of individual peptides in the context of different HLA‐B27 alleles broaden our perception of the possible pathogenetic role of this molecule in the development of AS and related spondyloarthopathies. In summary, the pathogenetic role of HLA‐B27 in AS seem to be quite heterogenous, and cannot be explained by a single mechanism, and new ideas have been raised based on the aberrant immunobiologic features of HLA‐B27.     

HLA class I alleles associated with susceptibility or resistance to human immunodeficiency virus type 1 infection among a population in Chaco Province, Argentina

Host genetic factors, such as HLA alleles, are important in human immunodeficiency virus (HIV) infection and its progression to AIDS. HLA class I gene products are involved in peptide presentation, and each allele is responsible for presenting a different set of peptides to cytotoxic T lymphocytes. The increase or decrease in the frequency of certain alleles in HIV-1-positive versus control subjects would suggest that alleles play a role in susceptibility to or protection against this viral infection. In the present study, 56 HIV-1-positive patients in Chaco Province, Argentina, were typed for the HLA-A and HLA-B loci, using polymerase chain reaction and sequence-specific oligonucleotide probes. The frequency of alleles A*24, B*18, and B*39 was increased in HIV-1-positive subjects, suggesting that these alleles play a role in susceptibility to HIV-1 infection. Alleles B*44 and B*55 were not found in HIV-1-positive subjects, suggesting that they have a protective effect against the disease. The P values of the alleles B*39 and B*44 were statistically significant (P<.05).     

Identification of previously unrecognized predisposing factors for ankylosing spondylitis from analysis of HLA–B27 extended haplotypes in sardinia

Objective

To define the contribution of HLA genes other than HLA–B27 in conferring susceptibility to ankylosing spondylitis (AS), through analysis of HLA–B27 haplotypes in Sardinian subjects.

Methods

Ninety‐eight patients with AS, 133 HLA–B27–positive controls (of whom 33 were positive for HLA–B*2709), and 190 randomly selected controls were genotyped for microsatellites and single‐nucleotide polymorphisms (SNPs) spanning the HLA region.

Results

Haplotypes carrying either the B*2705 or the B*2709 allele were found to share a conserved region downstream of the HLA–B gene and a functional polymorphism in the HLA–E gene (R128G), while differing in all other markers. Notably, the presence of an A at SNP rs1264457, encoding for Arg‐128, was significantly increased in the cohort of patients (P = 6 × 10⁻⁶, corrected P = 3 × 10⁻⁵) but not in B*2705‐ or B*2709‐positive controls. Comparing the alleles co‐occurring at each HLA marker, we identified a region differentiating patients with AS and B*2705‐matched controls. In particular, there was a markedly increased prevalence of heterozygosity at rs1264457 among B27‐positive controls (74%, versus 47% in patients and 54% in random controls), suggesting a protective role of G128 in AS. Moreover, other markers around the HLA–B gene were also differentially represented.

Conclusion

These results demonstrate a significant difference in the frequency of some HLA markers between AS patients and B*2705‐positive controls, which could be attributed to the opposite chromosome. In particular, the differential distribution of a functional polymorphism in the HLA–E gene suggests a possible role of natural killer function in AS pathogenesis.

     

HLA and susceptibility to juvenile idiopathic arthritis: a study of affected sibpairs in an isolated Finnish population

OBJECTIVE: To determine the effects of class I (A, B, and C) and II (DRB1 and DQB1) HLA loci alleles and DRB1-DQB1 haplotypes on genetic susceptibility to juvenile idiopathic arthritis (JIA) in families with 2 or more affected siblings. METHODS: A total of 83 affected siblings belonging to 38 families and corresponding to 50 affected sibpairs, their parents, and 45 healthy sibs were typed for HLA in A, C, B, DRB1, and DQB1 loci. Two study designs were used to explore linkage and association: a case-population control design and a family design using the linkage method: identical-by-descent (IBD) allele-sharing and the association analysis methods. Associations in family data were analyzed using the independent transmission disequilibrium test (TDT) for linkage in the presence of association. This was supplemented by the family-based association test (FBAT) to look for association in the presence of linkage, and is robust for population stratification and phenotype-based selection of data. RESULTS: Significantly increased HLA allele frequencies among the affected siblings compared to Finnish bone marrow donors were observed for HLA alleles Cw4 (odds ratio, OR, 1.7), B27 (1.8), B35 (1.7), and DR8 (3.7). The observed ratio of sharing 0, 1, and 2 HLA haplotypes (A, C, B, DRB1, and DQB1) among affected sibpairs (ASP) was 10:23:17, significantly different from expected (p < 0.001), using a formula that takes into account disease prevalence and the sibling recurrence risk. In the univariate association analysis, both independent TDT and FBAT found significantly increased transmission of the DRB1*0801 and DQB1*0402 alleles and Cw*0401. Independent positive allele effects of Cw*0401, DRB1*0801, and DQB1*0402 as well as negative effects of Cw*0701 and DQB1*0302 were shown by the family-based association analysis of the joint allele main effects. Multi-allelic test for association of each locus confirmed significant associations of the DRB1 and DQB1 loci in the risk of JIA. We found DRB1*0801/DQB1*0402 haplotype to be strongly associated (p < 0.001) with JIA, supporting findings of the haplotype associations-based ASP design. CONCLUSION: Both linkage analysis of the affected sibpairs and association analysis of nuclear families with JIA provided overwhelming evidence of the major contribution of HLA to genetic susceptibility to JIA. The association analysis of HLA-A, C, B, DRB1, and DQB1 alleles by both TDT and FBAT tests confirmed in the Finnish population that the most significant associations prevailed for DRB1*0801, DQB1*0402, as expected from previous observations, and supported the independent role of Cw*0401.     

Association and frequency of HLA-A, B and HLA-DR genes in south Tunisian patients with spondyloarthritis (SpA)

The aim of this study is to investigate the association of HLA-A, B and HLA-DR gene expression and to assess an association of additional HLA antigens besides HLA-B27 in south Tunisian patients with spondyloarthritis (SpA). Eighty-five patients diagnosed with ankylosing spondylitis (AS, n=68) and reactive arthrithis (ReA, n=17) were selected and compared with 100 healthy controls (HC). HLA class I antigens were typed serologically using microlymphocytotoxicity technique. HLA-DRB1* alleles were studied by polymerase chain reaction amplification with sequence-specific primers. The significance of differences between patients and controls was tested by chi-square analysis. We found significantly increased frequencies of HLA-A3 (30.6%; pC=0.04; OR=2.95), HLA-B27 (62.35%; pC=4.10(-17), OR=53.55), and HLA-DRB1*15 (17.2%; pC=0.026; RR=2.58) alleles in SpA patients compared to HC. The most frequent and strongest association was observed for HLA-B27 in AS (pC=6.6 ×10(-16), OR=52.23). When AS and ReA patients were analysed separately, HLA-DRB1*15 and HLA-A3 were increased only in AS (pC=0.01, OR=2.99 and pC=0.03, OR=3.14, respectively). In ReA patients, HLA-DRB1*04 (p=0.033, pC=NS, OR=2.89) was found to be the most common allele. By analysing the HLA-B27-negative subgroup, HLA-A3 and HLA-DRB1*15 expression was found to be dependent on the presence of HLA-B27. HLA-B27 expression was higher in male (45/53; 85%) as compared to female (8/53; 15%) patients (p=0.03). Apart from HLA-B27, HLA-A3 and HLA-DRB1*15 are the MHC class I and II alleles found most frequent in Tunisian patients with AS, whereas HLA-DRB1*04 was found most frequent in ReA patients. HLA-B27 is more frequent in male than in female patients.     

Update: the twenty subtypes of HLA-B27

HLA-B27 is a serologic specificity that encompasses 20 different alleles-HLA-B*2701 to B*2720. These alleles are also called subtypes of HLA-B27, and they have evolved from the B*2705 subtype, mostly from changes in exons 2 and 3 (which encode the alpha 1 and alpha 2 domains of the peptide binding groove, respectively). Occurrence of ankylosing spondylitis (AS) or related spondyloarthropathy (SpA) has thus far been documented in subjects possessing any one of the first 10 subtypes. However, B*2706 in Southeast Asian and B*2709 in the Italian island population of Sardinia may have a relatively much weaker association with AS. The 10 most recent subtypes have not yet been studied for disease association. There may exist a hierarchical ranking, resulting, in part, from differences in other co-inherited genetic factors, or due to environmental factors; eg, B*2705 is clearly disease-associated throughout the world, but not among the West Africans of Senegal and Gambia. It is important to investigate whether certain subtypes show any preferential association with some of the clinical features or forms of AS and related SpA among the various ethnic/racial populations and geographic regions of the world. This may help to identify the polymorphic positions of HLA-B27 that may have a disease-predisposing role.     

Undifferentiated spondyloarthropathies in Brazilians: importance of HLA-B27 and the B7-CREG alleles in characterization and disease progression

OBJECTIVE: To analyze the profile of the HLA-B27 and B7 cross-reactive group (CREG) alleles and the role of these markers in disease characterization and progression in patients with undifferentiated spondyloarthropathies (uSpA). METHODS: A total of 80 patients with a diagnosis of uSpA (40 HLA-B27 positive and 40 HLA-B27 negative) were prospectively studied for 2 years. The control group consisted of 66 HLA-B27 positive and 112 HLA-B27 negative individuals without a history of seronegative SpA. HLA-B alleles were typed at low (B7-CREG alleles, i.e., B*7, B*54, B*55, B*56, B*40, B*42) or high resolution (B*27 alleles) using polymerase chain reaction-amplified DNA hybridized with sequence-specific oligonucleotide probes. RESULTS: HLA-B*2705 was the most frequent allele, observed in 92.5% of the patients and in 77% of the controls, followed by the HLA-B*2702, observed in 5% of the patients and in 12% of the controls. HLA-B*2704 was observed in only one patient (2.5%), and was absent in the control population. HLA-B*2703 (6%) and HLA-B*2707 (5%) alleles were observed only in controls. No associations between HLA-B*27 alleles or B7-CREG alleles and any specific manifestation of uSpA were observed. HLA-B27 positive patients more frequently presented juvenile onset SpA (p = 0.002) and progression to ankylosing spondylitis (AS) (p = 0.03) than did HLA-B27 negative patients. The B7-CREG alleles were observed in 5% of the HLA-B27 positive uSpA group, in 25% of the HLA-B27 negative uSpA group, in 7% of the HLA-B27 positive controls, and in 13% of the HLA-B27 negative controls; a significant association was observed between the presence of the B7-CREG and the HLA-B27 negative uSpA group (p = 0.012). CONCLUSION: The frequency of the HLA-B*2705 allele among the B27 positive uSpA patients of this series was closely similar to that reported for patients with ankylosing spondylitis (AS). The presence of HLA-B*27 alleles was associated with the progression to AS, and the presence of B7-CREG was associated with uSpA in the HLA-B27 negative group.     

Increase of HLA-DRB1*0408 and -DQB1*0301 in HLA-B27 positive reactive arthritis

OBJECTIVE—To study HLA class II association in reactive arthritis.
METHODS—63 patients with reactive arth-ritis and 46 with rheumatoid arthritis were included in the study. HLA-DR alleles were determined by using a sequence specific PCR method. Oligonucleotide hybridisation was used for definition of DRB1*04 subtypes and DQB1 alleles. HLA-B27 was determined by standard microcytotoxity test or by PCR. HLA-B27 subtyping was made by sequencing.
RESULTS—46 (73%) of 63 patients with reactive arthritis were HLA-B27 positive and 24 (38%) were HLA-DRB1*04 positive. When haplotypes were inferred according to the known associations between DRB1 and DQB1 alleles, the frequency of DRB1*04-DQB1*0301 haplotype was found to be 13% (12/92) in HLA-B27 positive reactive arthritis patients, in contrast to 0% in HLA-B27 negative reactive arthritis (P = 0.04) and 1% in random controls (P = 0.0009). However, this combination was also found in 5% of 84 HLA-B27 positive control haplotypes, showing a linkage disequilibrium between B27 and this particular class II haplotype. HLA-DRB1*0408 subtype was found in 8/24 (33%) of the HLA-DRB1*04 alleles in patients with reactive arthritis, accounting for most DQB1*0301 haplotypes, but only in 5/55 (9%) of the DRB1*04 alleles in random controls (P = 0.017). All reactive arthritis patients with this subtype were positive for HLA-B27. DRB1*04-DQB1*0302 haplotype was increased in patients with rheumatoid arthritis (28/92, 30%) compared with reactive arthritis (12/126, 10%) or with the controls (12/100, 12%; P = 0.003). HLA-B*2705 was by far the dominant B27 subtype both in reactive arthritis patients with the particular DRB1*0408-DQB1*0301 haplotype and in controls. It was found in 11 out of 12 DR analysed patients, as well as in 10 out of 11 randomly selected B27 positive controls.
CONCLUSIONS—Although no single class II allele was found to be increased among patients with reactive arthritis, HLA-B27, DRB1*0408, and DQB1*0301 might exert a haplotypic effect in the pathogenesis of reactive arthritis, or they may be markers of a subset of B27 haplotypes conferring susceptibility.

     

The role of HLA genes in familial spondyloarthropathy: a comprehensive study of 70 multiplex families

OBJECTIVES: To investigate whether HLA alleles, other than HLA-B27, influence predisposition to spondyloarthropathy (SpA) in multiplex families. METHODS: Seventy French families with at least two affected SpA members were recruited. Patients, and their first degree relatives were typed for HLA-A, B, C, and DR, and extended HLA haplotypes were determined. The distribution of HLA-A, C, and DR alleles carried on HLA-B27+ haplotypes in SpA families was compared with the distribution of these alleles among HLA-B27+ haplotypes in the French general population. Contribution to SpA susceptibility of HLA-A, B, C, and DR alleles, other than HLA-B27, was tested by transmission disequilibrium test. The contribution of HLA alleles to specific presentation features of SpA was examined. RESULTS: Frequencies of HLA-A, C, and DR alleles carried on HLA-B27+ haplotypes from SpA families were comparable with those seen in the French population, except for DR13 which was overrepresented among patients (pcorr<0.001). Most interestingly, the HLA-DR4 allele was transmitted in excess to patients with SpA, independently of linkage to HLA-B27 (pcorr=0.05), and in a direction opposite to that for HLA-B27+ unaffected siblings (pcorr=0.01). Finally, the distribution of HLA alleles was not related to the presentation feature of SpA. CONCLUSION: HLA predisposition to familial SpA appears not to be limited to HLA-B27, but some HLA-DR alleles also have a significant influence. In particular, HLA-DR4 contributes significantly to a genetic predisposition to SpA, which may have implications in our understanding of SpA pathogenesis.     

Genetic aspects of ankylosing spondylitis

There is substantial evidence strongly favouring a direct role for HLA-B27 in genetic susceptibility to ankylosing spondylitis (AS) and related spondyloarthropathies (SpA), although the underlying molecular basis has yet to be identified. HLA-B27 itself is a serologic specificity that encompasses 26 different alleles that encode 24 different subtypes - HLA-B*2701 to B*2725, with the exclusion of B*2722. [The B*2722 allele was deleted as an official WHO allele in April 2002, with a note that the reference cell has been shown to have the same sequence as B*2706. Thus, from now on, with this deletion of B*2722, there will be a "hole" among the HLA-B*2701 to B*2725 group of alleles]. The 24 HLA-B27 alleles (subtypes) seem to have evolved from the most widespread subtype, B*2705. Two B27 alleles have been reported to lack association with AS: B*2706 among Southeast Asian populations, and B*2709 among Sardinians. The distinction between the disease-associated subtypes and those that are not disease-associated may provide some clues to the actual role of HLA-B27 in disease pathogenesis. Genetic family studies in populations of European descent indicate that HLA-B27 contributes only 16 % of the total genetic risk for the disease. The genes in the Major Histocompatibility Complex (MHC) as a whole, that includes HLA-B27, account for about half of the genetic susceptibility for AS. This clearly indicates the presence of additional disease predisposing genes in the MHC region on chromosome 6, and genome-wide studies have identified many areas of interest on other chromosomes that may contain additional disease predisposing genes. Additional studies emanating from the recent mapping of the human genome is expected to lead to better understanding of the genetic basis of these and other rheumatic diseases. Genetic counselling and the use of HLA-B27 typing as an aid to diagnosis are also reviewed.     

HLA-B27 subtypes in Turkish patients with ankylosing spondylitis and healthy controls

The aim of this study was to determine human leukocyte antigen (HLA)-B27 subtypes frequency in ankylosing spondylitis (AS) and related spondyloartropathy (SpA) patients. Therefore, we investigated the differences in HLA-B27 subtypes between HLA-B27-positive patients and controls. Sixty six patients were included in this study (51 AS and 15 SpA). Thirty-five individuals were diagnosed with leukemia or chronic renal failure, and their donors without any rheumatological problem (no SpA history) were selected as the control group. HLA-B27 subtyping was performed by PCR-SSP (polymerase chain reaction with sequence-specific primer) method in serologically HLA-B27-positive 46 AS patients, 9 SpA patients and control group. When the frequency of HLA-B27 was 4.5% in Turkish population, this frequency was 90.2% in AS patients. Four different HLA-B27 subtypes found in AS patients were B*2705 (65.2%), B*2702 (26.1%), B*2704 (6.5%) and B*2707 (2.2%). In SpA patients, B*2705 and B*2702 found in equal frequency. Five B27 alleles were identified in our control group: B*2705 (54.3%), B*2702 (31.4) %, B*2703 (2.9%), B*2704 (2.9%) and B*2702/B*2705 (8.5%). Both in the patient group and in the control group, we also observed B*2705 as most frequent allele, and B*2702 was second common allele. Our results show that the frequency of HLA-B27 subtypes is not significantly different between patients and controls (P?>?0.10).     

HLA class II antigens (DR, DQ loci) and peripheral arthritis in ankylosing spondylitis.

Fifty one patients with ankylosing spondylitis (AS) were typed for HLA-A, B, C, DR, and DQ antigens. The antigen frequencies were compared with those of a normal population and with a B27 positive control group. All but one of the patients with AS were HLA-B27 positive. A positive linkage disequilibrium between Cw1, Cw2, DR1, and the B27 antigen was observed. Patients with AS showed a significant increase in DQw2 antigen compared with the B27 positive control group. No differences in antigenic frequencies were observed in patients having peripheral arthritis and patients with only axial involvement. Seven out of nine patients (78%) with an erosive peripheral arthritis were DR7 positive, suggesting that DR7 or genes closely linked could be related with a more aggressive peripheral joint involvement in patients with AS.     

Association of the KIR3DS1*013 and KIR3DL1*004 alleles with susceptibility to ankylosing spondylitis

Objective

The killer cell immunoglobulin‐like receptors (KIRs) form a group of regulatory molecules that specifically recognize HLA class I molecules. The aim of this study was to analyze the possible contribution of the KIR3DL1 and KIR3DS1 alleles, in addition to HLA–B27, in the susceptibility to ankylosing spondylitis (AS) in a population of individuals from Spain.

Methods

We genotyped the KIR3DS1 and KIR3DL1 alleles in 2 cohorts of patients with AS and healthy control subjects. In total, 270 patients with AS and 435 healthy, HLA–B27–positive matched control subjects from Spain were enrolled. The KIR3DS1 and KIR3DL1 alleles were genotyped by sequence‐specific oligonucleotide probe–polymerase chain reaction, and their association with AS was analyzed. All individuals were typed for HLA–B.

Results

The KIR3DS1*013 allele was solely responsible for the increased frequency of the activator receptor KIR3DS1 in patients with AS compared with healthy HLA–B27–positive control subjects (35.7% versus 22.6% [P = 10⁻⁶], odds ratio 1.90, 95% confidence interval 1.50–2.40). The increased frequency of the KIR3DS1*013 allele in patients with AS was independent of the presence or absence of the HLA–Bw4I80 epitope. Moreover, the null allele KIR3DL1*004 was a unique inhibitory KIR3DL1 allele that showed a negative association with AS in the presence of HLA–Bw4I80.

Conclusion

The increased frequency of the KIR3DS1*013 allele in patients with AS is clearly independent of the presence of the HLA–Bw4I80 epitope, whereas the presence of inhibitory allotypes such as KIR3DL1*004 demonstrated a negative association in patients with AS in the presence of HLA–Bw4I80. As a consequence, the influence of KIR genotypes on AS susceptibility would be mediated by a general imbalance between protective/inhibitory and risk/activating allotypes.

     

An update on the contribution of the MHC to as susceptibility

The 40-year-old association of HLA-B27 with ankylosing spondylitis is one of the best examples of disease association with a hereditary marker. Genomewide association and family studies suggest that other important major histocompatibility complex (MHC) influences are operative in ankylosing spondylitis (AS) susceptibility. HLA-B27 positive hepatitis C individuals are immunologically more efficient in combating viral infections such as HIV-1, hepatitis C, and influenza and less efficient in combating against certain bacteria (and perhaps other organisms) capable of surviving intracellularly. A recent representative population survey of the frequency of HLA-B27 in the USA found a lower frequency of HLA-B27 in older US adults, perhaps reflecting this. Other HLA class I and class II alleles have been implicated in AS susceptibility, the most consistent being HLA-B*40/B60 (B*40:01) but also B14, B15, A*0201, DRB1*04:04, and certain DPA1 and DPB1 alleles. Non-HLA MHC alleles have also been implicated, although many such studies have been inconsistent, likely due to power issues related to the low number of HLA-B27-negative AS patients examined. The best evidence is for major histocompatibility complex class I chain-related gene A (MICA) whose recognition by intestinal epithelial T cells expressing different V-delta-1 gamma/delta TCR further implicates the gut in AS pathogenesis. The HLA class I and class II and other non-HLA allelic associations underscore the importance of T cells in AS pathogenesis.