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The Journal of Immunology, 2003, 170: 5778-5785.
Copyright © 2003 by The American Association of Immunologists

Allospecific T Cell Epitope Sharing Reveals Extensive Conservation of the Antigenic Features of Peptide Ligands Among HLA-B27 Subtypes Differentially Associated with Spondyloarthritis1

Veronica Montserrat, Mercè Martí and José A. López de Castro2

Centro de Biología Molecular "Severo Ochoa" (Consejo Superior de Investigaciones Científicas and Universidad Autónoma de Madrid), Facultad de Ciencias, Universidad Autónoma de Madrid, Madrid, Spain


   Abstract
Top
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 References
 
HLA-B*2702, B*2704, and B*2705 are strongly associated with spondyloarthritis, whereas B*2706 is not. Subtypes differ among each other by a few amino acid changes and bind overlapping peptide repertoires. In this study we asked whether differential subtype association with disease is related to differentially bound peptides or to altered antigenicity of shared ligands. Alloreactive CTL raised against B*2704 were analyzed for cross-reaction with B*2705, B*2702, B*2706, and mutants mimicking subtype changes. These CTL are directed against many alloantigen-bound peptides and can be used to analyze the antigenicity of HLA-B27 ligands on different subtypes. Cross-reaction of anti-B*2704 CTL with B*2705 and B*2702 correlated with overlap of their peptidic anchor motifs, suggesting that many shared ligands have similar antigenic features on these three subtypes. Moreover, the percent of anti-B*2704 CTL cross-reacting with B*2706 was only slightly lower than the overlap between the corresponding peptide repertoires, suggesting that most shared ligands have similar antigenic features on these two subtypes. Cross-reaction with B*2705 or mutants mimicking changes between B*2704 and B*2705 was donor-dependent. In contrast, cross-reaction with B*2702 or B*2706 was less variable among individuals. Conservation of antigenic properties among subtypes has implications for allorecognition, as it suggests that shared peptides may determine cross-reaction across exposed amino acid differences in the MHC molecules and that the antigenic distinctness of closely related allotypes may differ among donors. Our results also suggest that differential association of HLA-B27 subtypes with spondyloarthritis is more likely related to differentially bound peptides than to altered antigenicity of shared ligands.


   Introduction
Top
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 References
 
Although the pathogenetic mechanism for the strong association of HLA-B27 with ankylosing spondylitis (AS)3 and other spondyloarthropathies (Spa) remains unknown, it may be related to the peptide-presenting function of this molecule (1). Among the large body of indirect evidence in support of this idea are reports that several HLA-B27 allotypes (B*2702, B*2704, B*2705, B*2707) are strongly associated to AS, whereas B*2706 and B*2709 are weakly or not associated (2, 3, 4, 5, 6, 7). This is suggestive of peptide involvement in the pathogenesis of Spa because subtypes differentially associated to AS differ only by one (B*2705/B*2709) or two (B*2704/B*2706) amino acid changes that are located in the peptide binding site and influence peptide specificity (8, 9, 10).

Peptide sequencing studies on HLA-B27 subtypes differentially associated to AS demonstrated that subtype polymorphism influences mainly the type of C-terminal residue accepted, with little or no influence on the main anchor motif of HLA-B27, Arg2. Whereas B*2705 binds peptides with C-terminal basic, aliphatic, or aromatic residues, B*2709 accepts mainly peptides with aliphatic and Phe residues, with few exceptions (11, 12, 13). B*2704 binds peptides with aliphatic, aromatic, and less frequently, Arg residues, but B*2706 shows strong restriction for C-terminal aliphatic residues and Phe (14, 15). Comparative biochemical analyses have established that subtypes have largely overlapping peptide repertoires, but also bind differential peptide subsets. For example, B*2704 and B*2706 each share 88% and 90% of their peptide repertoires, respectively, and bind 10–12% of peptides not found in the other subtype (15). Thus, differential association of these two subtypes to AS might be related to the relatively small peptide subsets differentially bound to one subtype.

However, a critical question remains concerning the antigenic features of shared ligands bound to distinct subtypes. For instance, a peptide potentially involved in the pathogenesis of AS could be a ligand of only disease-associated subtypes or a shared ligand predisposing to disease only when presented by AS-associated subtypes.

The antigenic features of HLA-B27 ligands in complex with distinct subtypes are difficult to analyze directly. Viral epitopes are recognized by some CTL clones on multiple HLA-B27 subtypes, whereas other clones are subtype-specific (16, 17), thus dissociating peptide binding and T cell recognition. Recent x-ray diffraction studies have shown that a same peptide bound to B*2705 and B*2709 adopts a similar conformation on both complexes, suggesting that a TCR could recognize the peptide on both subtypes. However, subtle conformational differences were observed between both complexes, which might be distinguished by a given TCR (18). Therefore, crystallography alone cannot fully determine the antigenic features of a peptide in multiple contexts.

An alternative way to approach this issue is to use alloreactive CTL raised against a given HLA-B27 subtype, and test their cross-reactions with other subtypes. Alloreactive CTL are directed against many endogenous peptides constitutively bound to the alloantigen (19, 20, 21). Thus, they are very useful to test the antigenic features of HLA class I ligands on distinct subtypes.

A limitation of this approach is that in general the peptide epitope recognized by a given CTL clone is unknown. In a previous study one such peptide was identified and used to demonstrate that cross-reaction of the corresponding CTL clone with various HLA-B27 subtypes was due to recognition of the same peptide (22). Although this analysis cannot be conducted with most alloreactive CTL, it is possible to correlate the reaction patterns of CTL clones with HLA-B27 subtypes with the overlap among subtype-bound peptide repertoires. From this, the relationship between peptide and T cell epitope sharing can be established. This closely reflects the extent to which shared ligands maintain or alter their antigenic features when bound to different subtypes. This analysis, if conducted on unrelated donors, may show whether the antigenic features of HLA-B27 subtypes are perceived equally or differently by different individuals.

In the present study we raised alloreactive CTL from various HLA-B27-negative donors against the AS-associated B*2704 subtype, tested numerous CTL clones for recognition of other disease-associated (B*2702 and B*2705) or nonassociated (B*2706) subtypes, and correlated clonal reaction patterns with the known relationships among subtype-bound peptide repertoires. In addition, we used site-directed mutants to analyze the contribution of individual subtype changes to the allospecificity of B*2704 and B*2705. The results of our study are relevant to our understanding of the association of HLA-B27 with Spa, but have more general implications concerning the role of subtype polymorphism in alloreactivity. This is of increasingly clear importance because much of the diversity of HLA class I molecules is due to extensive polymorphism within each classical serologic specificity.


   Materials and Methods
Top
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 References
 
Cell lines

Human lymphoblastoid cell lines (LCL) used as stimulators for generating specific CTL clones (Table I) were grown in RPMI 1640 medium supplemented with 10% heat-inactivated FBS (both from Life Technologies, Paisley, U.K.). HMy2.C1R (C1R) is a LCL with low expression of its endogenous class I MHC Ags (23, 24). C1R transfectants expressing high levels of B*2702, B*2704, B*2705, B*2706, or HLA-B27 mutants (see below) were used. C1R cell lines were grown in DMEM (Life Technologies) with 10% heat-inactivated FBS.


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  		Table I. Responder/stimulator combinations for obtaining anti-B*2704 CTL

 
HLA-B*2704-specific CTL and cytotoxicity assay

B*2704-specific CTL clones were obtained from five HLA-B27-negative donors (Table I). About 106 PBMC were stimulated in vitro for a week with a mixture of 105 B*2704+ LCL and 106 autologous PBMC irradiated at 80 Gy and 50 Gy, respectively. Responder cells from the primary MLC were stimulated weekly in the same conditions, in the presence of 30 U/ml rIL-2 (a kind gift of Hoffmann-LaRoche, Nutley, NJ). Responder-stimulator combinations used are shown in Table I. T cell clones were obtained by seeding serial dilutions of stimulated T cells in U-bottomed 96-well plates containing 2000 irradiated stimulator LCL and 20,000 irradiated PBMC per well in the presence of 30 U/ml rIL-2. Cells in wells growing below the statistical limit for clonality were screened for HLA-B27 reactivity using a standard 51Cr release cytotoxicity assay (25) against B*2704-C1R targets, using untransfected C1R cells as a negative control.

MLC were grown in IMDM with glutamax I (Life Technologies), supplemented with 100 U/ml penicillin, 0.1 mg/ml streptomycin sulfate, and 0.05 mg/ml gentamicin (all from Sigma-Aldrich, St. Louis, MO) and 14% FBS (Life Technologies). T cell clones were grown in the same medium and restimulated weekly as previously described in the presence of IL-2.

HLA-B27 mutants

Two site-directed mutants mimicking individual amino acid changes between B*2704 and B*2705 were used: S77D and E152V. These mutants were derived from B*2705 as previously described (26). B*2704 and B*2705 differ by the S77D, E152V, and G211A changes (10). Thus, the S77D mutant was obtained by changing V152 in B*2705 to E152V. The E152V mutant was obtained by changing D77 in B*2705 to S77D. Both mutants have A211, as in B*2705, and therefore differ from B*2704 also at this position, which is located in the {alpha}3 domain outside the peptide binding site. S77D and E152V are identical with the B*2705 mutants E152 and S77, respectively, used in previous reports from our laboratory (26), but they have been renamed in this study to reflect their amino acid changes relative to B*2704.


   Results
Top
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 References
 
Donor-dependent recognition of B*2705 by anti-B*2704 CTL

A total of 100 alloreactive CTL clones raised against B*2704 from five unrelated donors were tested for recognition of B*2704- and B*2705-C1R transfectant cells using a 51Cr release cytotoxicity assay and an E:T ratio of 1:1 (Table II). CTL clones whose lysis of B*2705 targets relative to the specific lysis of B*2704 cells was >=30% were considered to be totally (>70% relative lysis) or partially (30–70% relative lysis) cross-reactive. CTL whose relative lysis of B*2705 targets was <30% were considered to be noncross-reactive (Table III). These ranges were chosen based on the nature of experimental cytotoxicity values. Specific lysis of efficiently killed targets in our experimental conditions usually ranged from 40 to 80%, thus the 30% relative cytotoxicity cutoff limit corresponds to specific lysis from 12% to 24%, respectively. Lowering the cutoff limit below 30% would result in higher estimations of cross-reactivity, but to the risk of including as positive specific lysis values close to background levels. Relative cytotoxicity values of >=70% approach the experimental variation among individual cytotoxicity assays. A total of 36 CTL clones (36%) cross-reacted with B*2705 by these criteria. Cross-reaction between both subtypes was higher with anti-B*2704 than with anti-B*2705 CTL, which was only 15% in a previous study (27). This is consistent with the fact that the C-terminal peptide motifs of B*2704 are a subset of those of B*2705 (14, 15). Cross-reaction of anti-B*2704 CTL with B*2705 was donor-dependent. It was 8–33% in four of the five donors and much higher (81%) in donor V (Table III).


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  		Table II. Specific cytotoxicity of anti-B*2704 CTL toward C1R expressing HLA-B27 subtypes or mutantsa

 

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  		Table IIA. Continued

 

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  		Table III. Cross-reaction of anti-B*2704 CTL with B*2705

 
Cross-reaction of anti-B*2704 CTL with mutants mimicking B*2705 polymorphism

Mutants S77D and E152V were used to assess the influence of individual subtype changes on allorecognition. A total of 69 and 64 anti-B*2704 CTL clones, respectively, were tested for lysis of the corresponding C1R transfectants (Table II and Table IV). Both changes had significant effect, abrogating recognition of 59% and 45% of the CTL, respectively.


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  		Table IV. Cross-reaction of anti-B*2704 CTL with the S77D and E152V mutants

 
As for B*2705, recognition of the mutants was donor-dependent. Cross-reaction with S77D ranged from 33 to 75% of the CTL from L, M, Me, and JY, although few CTL clones were tested from the latter two donors. In contrast, only 6% of the CTL from donor V cross-reacted with this mutant. E152V was recognized by 25–48% of the CTL from the former four donors and by 100% of the CTL from donor V. Thus, anti-B*2704 CTL from four donors were significantly affected by both mutations, whereas those from donor V were much more dependent on residue 77.

Interacting effects of residues 77 and 152 on allorecognition

We next examined the relationship between cross-reaction of anti-B*2704 CTL with B*2705 and recognition of individual mutants. A total of 63 CTL clones were analyzed, including 20 cross-reactive and 43 noncross-reactive with B*2705. Four reaction patterns were possible: CTL cross-reactive with both mutants (reaction pattern 1); only with E152V (reaction pattern 2A); only with S77D (reaction pattern 2B); or affected by both mutations (reaction pattern 2C). These reaction patterns were assigned the prefix (+) (i.e., +1, +2A, etc) or (-) (i.e., -1, -2A, etc) for CTL cross-reacting or not with B*2705, respectively. Representative examples are shown in Fig. 1.



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  		FIGURE 1. Reaction patterns of anti-B*2704 CTL with B*2705, S77D, and E152V. Reaction patterns were classified according to cross-reaction with B*2705 (+) or lack of it (-), and according to cross-reaction with both mutants (reaction pattern 1), only E152V (2A), only S77D (2B), or none of the mutants (2C). Representative examples of CTL clones with each of these reaction patterns are shown. Data are expressed as percentage of lysis relative to B*2704 targets. Specific cytotoxicity of these CTL clones toward the corresponding targets is given in Table II.

 
Among the CTL cross-reactive with B*2705 (Table V), 7 (35%) cross-reacted with both mutants (reaction pattern +1) and 13 (65%) failed to recognize one or both mutants. Thus for this latter subgroup (reaction patterns +2A and +2C), presence of the two amino acid changes between B*2704 and B*2705 had less effect on allorecognition than did a single change. S77D was more detrimental than E152V (reaction patterns +2A and +2C, and +2C, respectively). A significant difference was observed between donors M and V in the frequency of these reaction patterns. Thus, recognition of B*2705 was mainly due to lack of effect of individual mutations in donor M (reaction pattern +1) and to a compensatory effect of the E152V change over the abrogation of lysis by S77D (reaction pattern +2A) in donor V.


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  		Table V. Effect of individual mutations on cross-reaction of anti-B*2704 CTL with B*2705a

 
Among the CTL noncross-reactive with B*2705 (Table V), 16% were unaffected by any of the individual mutations (reaction pattern -1), indicating a cumulative effect of both mutations on abrogating allorecognition, 23% were affected by both individual mutations, and similar percentages (28% or 33%) were affected by one but not the other mutation. Again the distribution of individual reaction patterns was donor-dependent. For instance, lack of cross-reaction with B*2705 was due to the effect of only S77D (reaction pattern -2A) in all CTL tested from donor V, whereas a significant percentage of the CTL from other donors were affected by the E152V change (reactions patterns -2B and -2C).

High cross-reaction of anti-B*2704 CTL with B*2702

B*2704 and B*2702 differ by five amino acid changes located in {alpha}1 (positions 77, 80, 81), {alpha}2 (position 152), and {alpha}3 (position 211). Of these, residues 80 and 152 are accessible to the TCR.

A total of 35 anti-B*2704 CTL from three donors were analyzed for cross-reaction with B*2702 (Table II and Table VI). Of these, 22 (63%) CTL cross-reacted with B*2702 and 13 (37%) failed to cross-react. These results suggest that many shared ligands of B*2704 and B*2702 are similarly recognized by allospecific CTL on both contexts. The two donors, V and M, from whom sufficient CTL clones were tested with B*2702 showed little difference (71% and 63%) in the cross-reaction with this subtype.


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  		Table VI. Cross-reaction of anti-B*2704 CTL with B*2702

 
High cross-reaction of anti B*2704 CTL with B*2706 correlates with peptide sharing

B*2704 and B*2706 differ in two amino acid changes, H114D and D116Y, which are located in the {beta}-pleated sheet floor of the peptide binding site and are not accessible to the TCR. B*2704 shares 88% of its peptide repertoire with B*2706 (15).

Of 69 anti-B*2704 CTL tested from donors V, L, M, Me, and JY, 72% cross-reacted with B*2706 and 28% failed to recognize this subtype (Table II and Table VII). These results correlate well with the degree of peptide sharing between B*2704 and B*2706, suggesting that a majority of the shared ligands are similarly recognized by anti-B2704 CTL on both contexts. Yet, the difference between the percent of peptide sharing and the percent cross-reaction suggests that ~16% of shared ligands are not recognized by anti-B*2704 CTL in the B*2706 context.


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  		Table VII. Cross-reaction of anti-B*2704 CTL with B*2706

 
No significant difference was observed among donors in the frequencies of CTL cross-reactive and noncross-reactive with B*2706. However, some differences were apparent if CTL totally or partially cross-reactive were considered separately. These differences might simply reflect experimental error in the cytotoxicity assay. However, because they may also result from recognition of peptides expressed in different amounts or with slightly altered antigenic properties on both subtypes, these differences might be compatible with recognition of distinct sets of allospecific epitopes by cross-reactive CTL from different donors.

Reaction patterns of anti B*2704 CTL and subtype association to AS

The reactivity of 35 CTL clones from donors V, M, and JY with B*2704, B*2705, B*2702, and B*2706 was analyzed to assess the degree of shared epitopes and to correlate clonal reaction patterns with the peptide motifs favored by these subtypes and with association to AS. Seven of the eight possible reaction patterns (designated I to VIII) with the four subtypes were found, reflecting the diversity of the allospecific response against B*2704 (Table VIII).


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  		Table VIII. Cross-reaction of anti-B*2704 CTL with HLA-B27 subtypes associated or not to AS

 
Two aspects of this analysis are worth noting. First, the two predominant clonal patterns were the most cross-reactive ones: VIII and VII, accounting for 34% and 26% of the CTL tested, respectively. This reflects the substantial overlap among subtype-bound peptide repertoires and indicates that many shared ligands maintain their conformation and antigenic properties largely unaltered on multiple subtypes. Second, T cell epitopes shared by AS-associated subtypes (B*2704, B*2705, B*2702) but not B*2706 (reaction pattern V) were not found among the 35 CTL tested. Presumably, these type of epitopes would involve shared ligands that are bound to the three AS-associated subtypes with similar antigenic properties and are not bound to, or are presented differently by, B*2706. This type of peptide has features expected from a putative arthritogenic peptide. Thus, our results suggest that these peptides might not exist or be rare (<3%) in the HLA-B27-bound peptide repertoires.


   Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
References
 
This study was undertaken to address: 1) whether the antigenic features of shared ligands in the context of distinct HLA-B27 subtypes are conserved or altered; 2) whether the alloantigenic specificity of subtypes is due to differentially bound peptides, differential antigenicity of shared ligands, or both; 3) whether polymorphic residues among subtypes directly influence alloreactivity independently of their influence on peptide binding; and 4) whether different individuals respond similarly or differently to particular HLA-B27 epitopes. Both exposed residues of the MHC molecule and constitutively bound peptides shape the alloantigenic epitopes (22, 28, 29). Therefore, a molecular interpretation of HLA-B27 allorecognition must take into account the influence of subtype polymorphism on peptide specificity and whether polymorphic residues are accessible to the TCR or buried into the peptide binding site. Among the four subtypes tested in this study, residues 80 and 152 are exposed, whereas residues 77, 81, 114, and 116 are buried (Table IX). Thus, cross-reaction of anti-B*2704 CTL with B*2705 or B*2702 can be directly influenced by exposed residues. However, cross-reaction with B*2706 should be mainly determined by peptide recognition.


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  		Table IX. Polymorphism and peptide specificity of HLA-B27 subtypes

 
The percentage of cross-reaction of anti-B*2704 CTL with B*2705 or B*2702 was 36% and 63%, respectively. Although direct peptide comparisons between B*2704 and these two subtypes have not been conducted, from the higher similarity of C-terminal peptide motifs (Table IX) it can be inferred that peptide sharing of B*2704 is larger with B*2702 than with B*2705, which correlates with lower cross-reaction with this subtype. This is despite the fact that B*2704 is structurally closer to B*2705. Therefore, our results suggest that cross-reaction of anti-B*2704 CTL with B*2705 and B*2702 is related to recognition of shared ligands and does not correlate with structural similarity among subtypes. Furthermore, they suggest that of the CTL clones tested with all four subtypes, nearly all of those cross-reacting with B*2705 and B*2702 (Table VIII, reaction patterns V and VIII) also cross-reacted with B*2706, whose peptide motifs are a subset of those of the other subtypes, which strongly suggests recognition of shared ligands. A direct influence of exposed residues, or altered conformation of shared ligands, may influence allorecognition. However, because B*2704 differs from both B*2705 and B*2702 by the exposed E152V change, the relatively low cross-reaction with B*2705 is unlikely to be simply a consequence of this change.

Donor-related differences were observed in allorecognition of B*2705 and mutants related to this subtype, although not, or much less, with B*2702. For instance, donor V differed from donors L and M in a much higher cross-reaction with B*2705 and E152V and a much lower cross-reaction with S77D. This suggests that CTL from donor V are much more dependent on bound peptides, which would be affected by the S77D change (30), than on recognition of the exposed residue 152, which has less influence on the peptide specificity of HLA-B27 (31). For donors L and M, both mutants had similar effects on allorecognition, indicating a significant contribution of peptides and the MHC molecule to the alloantigenic epitopes recognized by CTL from these donors.

Thus, the alloreactive CTL response against B*2704 in different individuals is directed against distinct sets of allospecific epitopes. This must depend on the shaping of individual T cell repertoires and, therefore, on the HLA phenotype of the individual, but the precise features determining the outcome of the alloresponse remain undefined. However, the fact that the HLA type of the responder may influence the way in which HLA-B27 is perceived as an Ag raises the possibility that in HLA-B27-positive individuals the contribution of non-B27 MHC Ags to shaping the T cell repertoire will influence the immunogenicity and antigenicity of peptides presented by HLA-B27. Thus, if these are involved in Spa (32), the arthritogenic potential of a given peptide may be variable among individuals. This might contribute, along with other factors, to explain why only a small fraction of B27-positive individuals actually develop Spa.

A major goal of this study was to analyze the antigenic relationship between the differentially AS-associated B*2704 and B*2706 subtypes and how this relates to the high overlap between their peptide repertoires (Table IX). Because the two amino acid changes between B*2704 and B*2706 are located at the bottom of the peptide binding site (Table IX), the reactivity of anti-B*2704 CTL with B*2706 must essentially reflect recognition of bound peptides. Global cross-reaction with this subtype (72%) was only slightly lower than the overlap of the B*2704-bound peptide repertoire with that of B*2706 (88%), with little differences among individual donors. This strongly suggests that most of the shared ligands maintain similar antigenic properties on both subtypes. Presumably, of the 28% anti-B*2704 CTL not cross-reactive with B*2706, ~12% might recognize B*2704 ligands absent from B*2706 and ~16% might recognize shared ligands that are antigenically altered on B*2706. High correlation between allospecific CTL cross-reaction and peptide sharing was also observed in previous studies with B*2705 and B*2709 (13, 33), two subtypes differentially associated to AS that differ only in the buried residue 116 (7), and between B*2705 and B*2702 (34).

Although the three-dimensional structure of peptides in complex with B*2704 or B*2706 has not been analyzed, our results are consistent with a recent x-ray diffraction study (18) showing that a same peptide bound to B*2705 and B*2709 adopted a similar conformation on both complexes. Yet, subtle conformational differences in the central peptide region were observed, which might be sufficient to abrogate cross-reaction by some CTL.

An implication of our results is that if association of HLA-B27 with AS is related to presentation of an arthritogenic peptide to CTL (32), the differential association of B*2704 and B*2706 to this disease would be more likely due to differentially bound peptides than to alteration of antigenic features of a shared ligand.

Finally, the fact that 65% of the anti-B*2704 CTL tested recognized three or more subtypes further supports that the antigenic properties of shared ligands in complex with different subtypes are largely conserved. Yet, 11% of the CTL recognized B*2704-specific epitopes that were absent in other subtypes. This may reflect absence of the peptide epitope, altered conformation of the peptide, or direct interference of polymorphic HLA-B27 residues. Thus, conserved conformation of shared ligands on multiple subtypes is likely to be higher than reflected in the frequency of clonal cross-reactions.

In conclusion, our study suggests that in the absence of polymorphism at exposed residues (B*2704/B*2706), allorecognition of HLA-B27 subtypes by anti-B*2704 CTL closely correlates with the overlap of subtype-bound peptide repertoires, implying conservation of the antigenic features of many shared ligands. This applies to donors showing otherwise differences in their allospecific responses. Even among subtypes differing at exposed residues (B*2704/B*2702/B*2705), substantial CTL cross-reaction further indicated antigenic conservation of shared ligands. On this basis, we would like to suggest that a putative arthritogenic peptide would probably be one bound to AS-associated subtypes in an antigenically similar conformation and absent from subtypes not associated to AS. Alternatively, it might be a peptide selectively bound to subtypes not associated to AS (35). However, subtype-dependent differences in the antigenic features of shared ligands are less likely to account for HLA-B27 association to disease.


   Footnotes
 
1 This work was supported by Grants SAF99/0055, PM99-0098, and SAF2002/00125 from the Ministry of Science and Technology and 08.3/0005/2001.1 from the Comunidad Autónoma de Madrid. We thank the Fundación Ramón Areces for an institutional grant to the Centro de Biología Molecular "Severo Ochoa". Back

2 Address correspondence and reprint requests to Dr. José A. López de Castro, Centro de Biología Molecular "Severo Ochoa", Facultad de Ciencias, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain. E-mail address: aldecastro{at}cbm.uam.es Back

3 Abbreviations used in this paper: AS, ankylosing spondylitis; Spa, spondyloarthropathies; LCL, lymphoblastoid cell line; C1R, Hmy2.C1R. Back

Received for publication December 16, 2002. Accepted for publication March 18, 2003.


   References
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 

  1. Ramos, M., J. A. Lopez de Castro. 2002. HLA-B27 and the pathogenesis of spondyloarthritis. Tissue Antigens 60:191.[Medline]
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V. Montserrat, B. Galocha, M. Marcilla, M. Vazquez, and J. A. Lopez de Castro
HLA-B*2704, an Allotype Associated with Ankylosing Spondylitis, Is Critically Dependent on Transporter Associated with Antigen Processing and Relatively Independent of Tapasin and Immunoproteasome for Maturation, Surface Expression, and T Cell Recognition: Relationship to B*2705 and B*2706
J. Immunol., November 15, 2006; 177(10): 7015 - 7023.
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