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Rheumatology Advance Access originally published online on August 27, 2006
Rheumatology 2006 45(11):1338-1344; doi:10.1093/rheumatology/kel305
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© The Author 2006. Published by Oxford University Press on behalf of the British Society for Rheumatology. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Consistent patterns of expression of HLA class I free heavy chains in healthy individuals and raised expression in spondyloarthropathy patients point to physiological and pathological roles

T. Raine, D. Brown, P. Bowness1, J. S. Hill Gaston2, A. Moffett, J. Trowsdale and R. L. Allen

Department of Pathology, Tennis Court Road, Cambridge CB2 1QP, 1Human Immunology Unit, Institute of Molecular Medicine, Oxford OX3 9DS and 2Department of Medicine, Addenbrookes Hospital, Cambridge CB2 2QQ, UK.

Correspondence to: Rachel L. Allen, DPhil, Department of Pathology, Tennis Court Road, Cambridge, CB2 1QP, UK. E-mail: rla25{at}cam.ac.uk


   Abstract
Top
 Abstract
Introduction
 Patients and methods
 Results
 Discussion
 Conclusions
 Acknowledgements
 References
 
Objectives. Major histocompatibility complex class I (MHC-I) proteins exist at the cell surface in antigen presenting forms and as ß2m-independent free heavy chains (FHCs). FHCs have been implicated in spondyloarthritis, but little is known about their expression in healthy individuals. We studied FHC expression on various human cell types, comparing spondyloarthropathy patients with healthy and rheumatoid arthritis (RA) patient controls.

Methods. MHC-I expression was analysed by flow cytometry. FHC levels were normalized for overall MHC-I to generate a relative expression level. Relative FHC levels were analysed for peripheral blood and trophoblast samples from healthy volunteers, RA and spondyloarthropathy patients. Macrophages and dendritic cells were cultured in vitro to analyse changes following activation. Peripheral blood leucocytes from patients with ankylosing spondylitis (AS) and RA were treated with inflammatory stimuli and subsequent alterations in their relative FHC levels were analysed.

Results. We found consistent patterns of differential relative FHC expression across lymphocyte subpopulations and particularly high expression on extravillous trophoblast. FHCs were present at higher levels in a reactive arthritis (ReA) population than in healthy controls and RA patients; differences not merely due to the presence of Human Leucocyte Antigen (HLA) B27. Treatment of leucocytes from arthritic patients with bacterial lipopolysaccharide resulted in significant up-regulation of FHC compared with an HLA B27+ control population.

Conclusions. Our findings define normal levels and tissue expression of FHCs, and support the hypothesis that disregulation of heavy chain expression may play a pathogenic role in spondyloarthropathy.

KEY WORDS: Free heavy chain, Ankylosing spondylitis, MHC, FHC, HLA B27, HLA G


   Introduction
Top
 Abstract
 Introduction
Patients and methods
 Results
 Discussion
 Conclusions
 Acknowledgements
 References
 
Major histocompatibility complex class I (MHC-I) proteins are best known for their role in antigen presentation; a trimolecular complex of MHC-I heavy chains combined with ß2m and peptide forms an antigen-presenting structure which is specifically recognized by the T Cell Receptor (TCR) on CD8+ cytotoxic T cells (CTL). The trimolecular MHC-I complex also controls the activity of natural killer (NK) cells and T cells through its recognition by receptors from the killer Ig like receptor (KIR) family. A third family of MHC-I receptors is found mainly on cells of the myelomonocytic lineage. These leucocyte Ig-like receptors (LILR) recognize MHC-I with a broad specificity, their ligands including classical and non-classical alleles in addition to trimolecular and ß2m-independent free heavy chain (FHC) forms [1]. Therefore, when we consider the multifunctional role of MHC-I in immune regulation, we must now include multiple forms of MHC-I in addition to multiple receptors for MHC-I.

FHC was originally believed to be an immunologically inert by-product of MHC-I biology but have been the focus of several recent studies as a result of their possible correlation with disease [2–10]. Newly synthesized MHC-I heavy chains are held in the endoplasmic reticulum until they form a stable trimeric complex and then progress to the cell surface (reviewed in [11]). At the cell surface, ß2m and peptide can dissociate, leaving membrane-bound FHC [12–14]. Although assembly with ß2m and peptide is a general prerequisite for progress from the ER, heavy chains of some MHC-I alleles can reach the cell membrane independently [7, 15]. Cell-surface FHCs have a relatively long half-life of several hours [13] and are removed by internalization or metalloproteinase cleavage [16, 17]. FHCs are known to be found at high levels on the surface of activated lymphocytes [17–20], where they have the potential to interact with other immune receptors, in cis or in trans [2, 9, 20, 21].

Several forms of FHCs can be identified at the cell surface [22], but the most stable may exist as disulphide-linked multimers. A murine study identified homodimers of MHC-I bonded through an internal cysteine residue [23], and the majority of human alleles carry a similar internal cysteine. Two alternative dimer structures have been identified for human alleles, disulphide bonded through extracellular cysteine residues in their {alpha}1 domain: FHC homodimers of HLA B27 disulphide-bonded through Cys67 were first documented by in vitro experiments, then subsequently identified in vivo [3, 6, 9, 24], and a parallel situation occurs for HLA-G through residue Cys42 [25, 26].

FHC structures have been implicated in the pathogenesis of spondyloarthropathies. This family of diseases shows a striking association with HLA B27, an association which was originally interpreted to imply a role for TCR recognition in the disease process. However, a growing body of knowledge on additional receptors for MHC-I and FHC forms of HLA B27 has generated a new wave of theories [1, 27, 28]. The best evidence for these theories has been provided by HLA B27 transgenic models of disease. In one mouse model, the presence of HLA B27 on a ß2m knockout background led to the appearance of an inflammatory arthritis similar to ankylosing spondylitis (AS). Disease incidence in this model could be reduced by treatment with an FHC-specific antibody [7]. Differences in severity for a similar disease in various lines of an HLA B27 transgenic rat appeared to correlate with levels of FHC homodimers [24]. Homodimers have also been detected in inflammatory arthritis patients [9], whilst high levels of FHC have been detected in monocytes from patients [10]. However, we need to address the fact that, in addition to HLA B27, FHC can arise from other alleles including HLA-A, HLA-B, HLA-C and HLA-G [19, 25, 26, 29] and that arthritic disease is observed in ß2m-deficient mice in the absence of HLA B27 [30].

Cell surface FHC can exist for various alleles of mouse and human MHC-I. Whilst most recent studies have been limited to FHC structures of one particular allele, HLA B27, little is known about the general biology of these forms. Therefore, in the present study, we characterize FHC expression in both healthy individuals and in samples from arthritic patient populations. If FHCs are nothing more than an immunologically inert waste products, it could be argued that any increase in their levels on the cell surface merely reflects a higher overall MHC-I expression observed in situations such as lymphocyte activation [17] or on antigen presenting cells. Therefore, we used a combination of FHC-specific and MHC-I-specific monoclonal antibodies to determine a value that represented the levels of FHC relative to overall MHC-I expression. Our results indicate that FHC levels are more than a simple function of overall MHC-I expression. Furthermore, extremely high relative levels of FHC were observed on trophoblast, a highly specialized tissue with restricted MHC-I expression, which leads us to hypothesize that any physiological function for FHC might be of particular importance in this tissue. We conclude that differences in the levels of FHC to MHC-I between cell types in healthy control individuals and cells of healthy and patient populations might indicate that these forms have an immunological function and raise the possibility that differences in this level could lead to different physiological and pathological outcomes.


   Patients and methods
Top
 Abstract
 Introduction
 Patients and methods
Results
 Discussion
 Conclusions
 Acknowledgements
 References
 
Blood samples
After written consent was obtained according to the declaration of Helsinki, leucocytes were harvested from heparinized blood by density centrifugation over Lymphoprep (Nycomed, Norway). Cells were washed twice in RPMI 1640 (Sigma-Aldrich, Poole, UK) and stored at –80°C in 20% DMSO/80% fetal calf serum. The mean age for the control group of individuals (9 male, 1 female) was 27. Our HLA B27+ control population (4 male, 4 female) had a mean age of 35. For the data shown in Fig. 1a and Table 1, peripheral blood and synovial fluid samples were acquired from 11 patients with acute reactive arthritis (ReA). Triggering organisms included Chlamydia and Yersinia. Out of eleven patients, six were HLA B27+ and all were men. The mean age of this patient group was 26. Samples were also acquired from six patients with rheumatoid arthritis (RA), all were women and the average age was 52.5 yrs. For the data shown in stimulation studies in Fig. 1b, samples were obtained from 10 patients previously diagnosed with AS but not known to be undergoing an acute inflammatory episode at the time of sampling. All were HLA B27+, two were female and the mean age was 55. Ethical permission was obtained from the Addenbrookes Hospital Ethics Committee and from the Central Oxford Research Ethics Committee.


Figure 1
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  		FIG. 1. FHC expression on spondyloarthropathy patients and controls. (a) Relative FHC on peripheral blood leucocytes gated on the lymphocyte population were compared between 11 patients with ReA, 6 patients with RA, 8 HLA B27+ healthy controls and 9 HLA B27- healthy controls. Boxed data points in the ReA group indicate that these patients were HLA B27+. (b) Peripheral blood leucocytes from 10 AS patients, 4 RA patients and 7 HLA B27+ healthy controls were treated with Salmonella LPS and analysed for MHC expression after 48 h. Results indicate alteration in relative FHC level from untreated cells. All P-values are from two-sided Mann–Whitney U-test.

 

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  		TABLE 1. Relative FHC level in paired blood and synovial fluid samples from patients with ReA

 
Trophoblast samples
Trophoblast cells were isolated as previously described [31]. Extravillous trophoblast was identified using a FITC-conjugated monoclonal antibody to HLA-G, a non-classical MHC-I protein known to be expressed on extravillous trophoblast [32].

Generation and stimulation of macrophages and dendritic cells in vitro
Buffy coats were obtained from healthy National Blood Service donors. Peripheral blood leucocyte (PBL) were isolated and resuspended at a density of 1 x 107 and adhered to six well plates for 1 h. Plates were washed and adherent cells cultured in 1% autologous serum. Macrophages were differentiated in the presence of M-CSF (Peprotech, London, UK) at 50 ng/ml, whilst dendritic cells were differentiated with IL-4 (Peprotech) at 50 ng/ml and GM-CSF (Peprotech) at 50 ng/ml. On day 7, dendritic cell cultures were activated with Salmonella enteritidis lipopolysaccharide (LPS) (Sigma-Aldrich) at a concentration of 10 ng/ml and macrophage cultures were stimulated with LPS (10 ng/ml) and IFN{gamma} (Biosource, Nivelles, Belgium) at 50 ng/ml. Prior to staining, cells were resuspended by incubation in 10 mM EDTA. Macrophage activation was confirmed by staining for CD105 and dendritic cell activation was confirmed by staining for HLA-DR and CD86.

Cytokine stimulation
Peripheral blood leucocytes were resuspended at a concentration of 1 x 106 ml and plated into 24-well plates. Cytokines and LPS were added to the following concentrations: IFN{gamma} (Biosource) 50 ng/ml, TGF-ß (Sigma-Aldrich) 0.1 ng/ml, Salmonella LPS 10 ng/ml and IL-4 0.4 ng/ml. Cells were incubated for 48 h prior to staining for flow cytometry.

Preparation of cells for flow cytometry
Antibodies used were W6/32 (Dako, Bucks, UK), HC10 (gift from Dr J. Lindquist), IgG2a Isotype control (Serotec, Oxford, UK), IgG1 Isotype control (Serotec), Rabbit-anti-mouse-FITC (Dako), CD3-PE (Dako), CD56-PE (Dako), CD14-PE (Sigma-Aldrich), anti-HLA DR/FITC (Dako), anti-CD3/Tricolor (Caltag, California, USA), anti-CD19/Tricolor (Caltag) and anti-CD105-PE (Serotec). Cell stainings were carried out at 4°C as previously described [33]. Prior to staining, cells were blocked in 1% normal human serum to prevent non-specific Fc receptor binding. Samples were analysed on a Becton Dickinson FACScan and analysed using Cellquest software (Becton-Dickinson, New Jersey, USA). Population fluorescence intensity measurements were made using the geometric rather than the arithmetic mean since the Becton Dickinson analysis software converts channel value into fluorescence intensity using a logarithmic algorithm. W6/32 is a conformation-sensitive antibody that binds to an epitope probably in the {alpha}2 helix of folded MHC-I and recognizes HLA-A, B, C and G alleles [34]. HC10 is an antibody raised against denatured MHC-I heavy chains and consequently recognizes ‘unfolded’ MHC-I of HLA-B, C and G alleles [35, 36]. Relative FHC level was expressed as a percentage of HC10:W6/32 geometric mean fluorescence intensities (MFIs).

Statistics
Appropriate statistical tests were performed on sample data using Prism analysis software (Graphpad Software, San Diego, USA). Exact P-values are given in figures, whilst P-values <0.05 are described in the text as being statistically significant.


   Results
Top
 Abstract
 Introduction
 Patients and methods
 Results
Discussion
 Conclusions
 Acknowledgements
 References
 
FHC expression on healthy leucocytes
We used two colour flow cytometry to characterize the expression of FHC across various cell subsets including CD3+ T lymphocytes, CD19+ B lymphocytes, CD56+ NK cells and CD14+ monocytes (Fig. 2). HC10 and W6/32 were selected as the antibodies with the broadest reactivity to FHC and folded structures, respectively, and were used to assess expression levels in parallel sets of samples. Samples from 10 healthy (HLA B27 negative) individuals were stained using these lineage-specific markers. Analysis of the geometric MFI revealed variations between individuals and cell lineages. For each individual studied, FHC staining (by HC10 reactivity alone) was highest on the CD14+ monocyte population. However, it has been argued that such findings may reflect a generally high level of MHC-I expression by these cells, with elevated levels of FHC a function of a constant rate of dissociation of classical MHC-I at the cell surface [4, 5, 37]. We, therefore, normalized FHC expression to levels of ß2m-associated MHC-I, expressing the result as a relative level to generate a percentage value of relative FHC expression as previously described by Sesma et al. [38]. When FHC levels were normalized for overall MHC-I expression, there was a significant tendency towards higher relative FHC levels on CD14+ leucocytes, though this effect was not observed for every individual as had been seen for HC10 reactivity alone (Fig. 2b). No significant patterns were observed for other leucocyte subsets.


Figure 2
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  		FIG. 2. Relative levels of FHC expression on peripheral blood leucocyte subsets. Peripheral blood leucocytes from 10 healthy controls were stained with antibodies to various cell surface markers in addition to W6/32 and HC10 antibodies for classically folded or FHC forms of MHC-I. (a) A representative profile for MHC-I staining, gated on a CD3+ T cell population shows detectable FHC expression on resting cells from a healthy control individual. (b) Comparison of relative FHC expression on leucocyte subsets for a healthy control population. Lines join leucocyte subsets for each individual in order to allow comparisons to be made between leucocyte subsets on an individual basis. P-values comparing leucocyte subsets are from two-sided Wilcoxon rank signed tests.

 
FHC expression on activated macrophages and dendritic cells
Previous studies have shown that FHC levels are higher on activated than on naïve T cells [17–20]. Therefore, we studied the effect of leucocyte activation upon FHC up-regulation for other cell subsets. Macrophages and dendritic cells were cultured and stimulated in vitro using standard protocols in order to study their expression of FHC following stimulation. For dendritic cell cultures, relative FHC was increased following LPS stimulation (Fig. 3a). The differences between stimulated and unstimulated cells were statistically significant (P = 0.03). No significant changes in relative FHC expression were seen for macrophages stimulated with IFN{gamma} and LPS (Fig. 3b).


Figure 3
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  		FIG. 3. Relative FHC expression on activated macrophages and dendritic cells. In vitro cultures of (a) dendritic cells and (b) macrophages were treated with LPS and LPS+IFN{gamma}, respectively, and then analysed for relative FHC expression. Results shown are for paired samples (treated and untreated) from seven separate experiments (six in the case of macrophages). P-values comparing unstimulated and stimulated subsets from two-sided Wilcoxon rank signed tests were significant for dendritic cells, but not for macrophages.

 
Extravillous trophoblast expresses high levels of FHC
The data described earlier suggest that relative FHC levels vary between different cell populations and different states of immune activation. Consequently, such differences could be taken to reflect a physiological role for FHC, possibly connected with regulation of an ongoing immune response. One situation where FHC might be particularly relevant is in the site that expresses HLA-G, a non-classical MHC-I which, like HLA B27, is known to form unusually stable FHC multimers [25, 39]. This site, the trophoblast, would be predicted to require extensive immunoregulation in order to prevent rejection of the fetus and is in contact with maternal leucocytes expressing high levels of receptors that are capable of binding FHCs [40]. Indeed, formation of HLA G multimers has been shown to enhance receptor binding and activity [26, 41] as has been hypothesized for HLA B27 [1]. Although one previous study documented that FHC could be found on the surface of trophoblast, there was no indication of relative expression levels [42]. To investigate further, we stained three samples of human extravillous trophoblast, again using W6/32 and HC10 as, in addition to binding classical HLA-A, B and C alleles, these antibodies also recognize HLA-G. W6/32 stainings were equivalent to or higher on trophoblast than on circulating leucocytes, but the MFIs for HC10 staining were particularly high, leading to the highest relative level for FHC observed in any of our experiments (Fig. 4). These results are likely to reflect the presence of FHC HLA G structures.


Figure 4
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  		FIG. 4. High relative expression of FHC on trophoblast. Relative FHC expression was compared for three trophoblast samples and for peripheral blood leucocytes from 10 healthy individuals gated on the lymphocyte population.

 
High levels of FHC are seen in spondyloarthropathy patients
While the very different nature of the tissues under study necessitates caution, we believe that the above findings could suggest a physiological role for FHC in immunoregulation. Given that FHCs have also been implicated in spondyloarthropathy, we hypothesized that normal processes involving FHC might become deranged in these diseases. We, therefore, examined the relative levels of FHC on leucocytes of spondyloarthropathy patients and controls. For these experiments, samples from ReA individuals were used as an example of an acute inflammatory spondyloarthropathy.

In our study, W6/32 stainings on peripheral blood leucocytes taken from patients during an episode of acute ReA did not show any consistent overall increase in MFI compared with controls. However, relative FHC levels for peripheral blood leucocytes were significantly higher in ReA patients than in HLA B27+ controls (Fig. 1a). Relative FHC levels were not higher for a population of RA patients than for healthy controls. One possible explanation for higher levels of relative FHC in ReA is that this disease is associated with HLA B27, an allele known to form homodimer FHC structures [3, 9]. However, increased relative levels of FHC in spondyloarthritis patients cannot be ascribed to expression of HLA B27 alone, as there was no significant difference in relative FHC expression between B27– and B27+ subsets of healthy controls. Comparison of paired blood and synovial fluid samples was performed for four patients (Table 1) in order to determine whether activated lymphocytes in situ influenced FHC expression. Although the relative level was increased in each case, the changes were minor.

Spondyloarthropathy patients show an increased tendency to express high levels of FHC
We next sought to investigate the possibility that leucocytes from disease-susceptible individuals might differ in their regulation of FHC expression, for example, in terms of changes in FHC expression in response to inflammatory cues. We compared the response of cells from our healthy control populations with a set of long-term AS patients and a set of RA patients. In these experiments, AS samples were used as an example of spondyloarthritic patients with a known disease susceptibility, but who were not known to be undergoing an acute inflammatory episode at the time of sampling. We studied the effects of various bacterial and cytokine stimuli reported to be present in the joints of spondyloarthropathy patients [43]. Peripheral blood leucocytes were cultured for 48 h in the presence of LPS, IL-4, IFN{gamma} or TGF-ß. No consistent differences in relative FHC expression were observed between patients and controls following treatment with IL-4, IFN{gamma} or TGF-ß. However, following treatment with LPS, patients with both AS and RA demonstrated a tendency to up-regulate FHC that was not observed for HLA B27+ healthy controls (Fig. 1b) and was statistically significant. These results indicate the possible existence of a predisposition towards increased FHC expression in arthritic patients, beyond simply the presence of HLA B27 or an inflammatory environment and offer intriguing possibilities for exploring disease pathogenesis.


   Discussion
Top
 Abstract
 Introduction
 Patients and methods
 Results
 Discussion
Conclusions
 Acknowledgements
 References
 
Previous work has documented FHC expression on the surface of human leucocytes, although it has not been clear whether this phenomenon was restricted to cells activated in vitro, or a more generalized occurrence. Here, we extend the knowledge of FHC biology by comparing levels of FHC relative to classical trimeric MHC-I across cell types and in different stimulatory contexts. We have shown increased relative levels of FHC on CD14+ blood monocytes compared with other leucocyte subsets, as well as on activated compared with immature dendritic cells, on extravillous trophoblast and during inflammatory arthritis compared with healthy controls. Importantly, we found that differences in FHC expression exist even after normalizing for classical MHC-I expression and within the different cell subsets of healthy control individuals.

MHC-I dissociation appears to be a common in vivo occurrence, as ß2m is found at significant levels in serum [44]. Our findings indicate that cell-surface FHC are not a simple function of overall MHC-I expression and, consequently, that they do not necessarily arise via a constant rate of MHC-I/ß2m dissociation. Alleles vary in their ability to form stable FHC structures, and alterations in the relative level of FHC may reflect varying expression patterns for the different alleles. Future studies may define what proportion of FHC come from each source and for which alleles. We believe that pathways of FHC trafficking and regulation will provide an interesting and fruitful area of investigation in this respect. While the biological significance of varying MHC levels on different circulating subsets is not yet clear, we sought to find a cell type which might provide a clearer indication of an immunoregulatory role.

Since relative FHC expression levels vary between cell types and tissues, we must consider the possibility of a biological role for these proteins. Receptors in the LILR family have been shown to bind FHC [2, 9], and alterations in relative FHC levels could thus have an immunological impact by altering the balance of cellular stimulation [1]. Critical to such a possibility is that the recognition of FHC might give differential results to ligation by classical MHC-I as seen for LILRB1 [25, 26]. Our findings that extravillous trophoblast expresses high relative levels of FHC suggest that any immunoregulatory roles might be important in this tissue. Inhibitory LILR capable of recognizing FHC are found in close proximity to trophoblast [40], and it has been hypothesized that this interaction could lead to the generation of an inhibitory environment [1].

In the converse situation, disregulation of any physiological process that involves FHC recognition might be expected to lead to recognizable pathogenic states. It has been suggested that FHC may play a role in the pathogenesis of spondyloarthropathy [1, 27, 28]. Previously, Cauli and colleagues [5] documented higher levels of HLA B27 in AS patients but did not see a significant difference in FHC between patients and controls. This is in contrast to another study, which showed high levels of FHC staining on monocytes from patients [10]. However, neither of these studies looked at the level of FHC relative to overall MHC-I. In our study, we found significantly higher levels of relative FHC expression in ReA patients compared with HLA B27+ healthy controls.

In our study, HLA B27 is not sufficient to predispose to high FHC levels, reflecting the fact that the majority of HLA B27+ individuals do not develop spondyloarthopathy. Also, whilst the spondyloarthropathies show a strong association with possession of this allele, HLA B27– patients do exist. Similarly, in mouse models, inflammation is observed in the absence of HLA B27 on certain backgrounds, where ß2m deficiency is sufficient to confer arthritic disease [30]. Therefore, it is possible that relative FHC expression levels are critical disease determinants, and that HLA B27 is particularly, but not uniquely, prone to forming stable FHC structures. It will be important to determine whether increase in FHCs are related to disease activity or disease causation.

In our study, LPS treatment increased the relative FHC level for AS and RA patients, but not for healthy controls. This provides the first demonstration that disease-prone individuals, for some as yet unknown reason whether genetic or as a consequence of the disease, show a predisposition towards increased FHC upon stimulation, an important effect if FHCs do indeed play a role in spondyloarthropathy. Consequently, exposure to bacterial products may shift the FHC expression profile of an AS individual in remission from that of a control to that of a patient and may thus provide a causal link between pathogen exposure and disease exacerbation.

We determined relative FHC levels for peripheral blood leucocytes of arthritis patients. Disregulation of heavy chain expression may play a pathogenic role in spondyloarthritis. If FHCs do play a role in disease, future studies must address which particular cell types are important for FHC expression and which (if any) are involved in FHC recognition. Synovial infiltrates include macrophages and dendritic cells, which are currently receiving a justified increase in attention [45–48]. We may now need to address how macrophages function in disease and whether their role involves expression and/or recognition of HLA B27. As members of the myelomonocytic lineage, CD14+ cells express receptors that can engage FHC [1]. Therefore, any HLA B27-mediated effects in spondyloarthropathy may occur through recognition by the dominant macrophage population of FHC. Macrophages in close proximity to trophoblast express inhibitory receptors that can recognize FHC [40]. Whether myelomonocytic cells in the inflamed joint express activating and/or inhibitory receptors that can recognize FHC has yet to be determined.


   Conclusions
Top
 Abstract
 Introduction
 Patients and methods
 Results
 Discussion
 Conclusions
Acknowledgements
 References
 
Our data demonstrate a variation in expression patterns of FHC across cell subsets in healthy control individuals that point to a possible physiological relevance of these structures, particularly in the highly immunoregulated environment of the placenta. We have also observed a propensity for expression of high relative levels of FHC in patients with spondyloarthropathies that cannot be accounted for simply by possession of HLA B27. Consequently, we believe that the implications of the present study are wide and suggest multiple avenues for future study, both in terms of the normal physiological roles of FHC and their involvement in the immunodisregulation associated with the significant burden of spondyloarthritic disease.

Formula


   Acknowledgements
Top
 Abstract
 Introduction
 Patients and methods
 Results
 Discussion
 Conclusions
 Acknowledgements
References
 
This work was supported by the Arthritis Research Campaign, R.A. is a Beit Memorial Fellow.


   References
Top
 Abstract
 Introduction
 Patients and methods
 Results
 Discussion
 Conclusions
 Acknowledgements
 References
 

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Submitted 15 June 2006; revised version accepted 21 July 2006.
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