Increased Levels of IgG Antibodies against Human HSP60 in Patients with Spondyloarthritis

Abstract

Spondyloarthritis (SpA) comprises a heterogeneous group of inflammatory diseases, with strong association to human leukocyte antigen (HLA)-B27. A triggering bacterial infection has been considered as the cause of SpA, and bacterial heat shock protein (HSP) seems to be a strong T cell antigen. Since bacterial and human HSP60, also named HSPD1, are highly homologous, cross-reactivity has been suggested in disease initiation. In this study, levels of antibodies against bacterial and human HSP60 were analysed in SpA patients and healthy controls, and the association between such antibodies and disease severity in relation to HLA-B27 was evaluated.Serum samples from 82 patients and 50 controls were analysed by enzyme-linked immunosorbent assay (ELISA) for immunoglobulin (Ig)G1, IgG2, IgG3 and IgG4 antibodies against human HSP60 and HSP60 from Chlamydia trachomatis, Salmonella enteritidis and Campylobacter jejuni. Disease severity was assessed by the clinical scorings Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), Bath Ankylosing Spondylitis Functional Index (BASFI) and Bath Ankylosing Spondylitis Metrology Index (BASMI).Levels of IgG1 and IgG3 antibodies against human HSP60, but not antibodies against bacterial HSP60, were elevated in the SpA group compared with the control group. Association between IgG3 antibodies against human HSP60 and BASMI was shown in HLA-B27+ patients. Only weak correlation between antibodies against bacterial and human HSP60 was seen, and there was no indication of cross-reaction.These results suggest that antibodies against human HSP60 is associated with SpA, however, the theory that antibodies against human HSP60 is a specific part of the aetiology, through cross-reaction to bacterial HSP60, cannot be supported by results from this study. We suggest that the association between elevated levels of antibodies against human HSP60 and disease may reflect a general activation of the immune system and an increased expression of human HSP60 in the synovium of patients with SpA.

A role for anti-HSP60 antibodies in arthritis: a critical review

“…IgG can be divided into four subclasses, IgG1-4, which are defined by a structural difference in the Fc receptor. In a recent study 21,22 HSP60 specific-antibodies were only present in the IgG1 and IgG3 isotypes, as discussed in the next section.…”

“…Therefore, the LPS is not immunogenic, but the lipid-A part is present, so it can activate toll-like receptor 4 (TLR-4) in cellular assays 31 . In the publications by Hjelholt et al and Carlsen et al 21,22 , it was found that the dominant subclass for human HSP60 in SpA is IgG3, while antibodies to bacterial HSP60 were dominated by IgG1 (Figure 4). In both studies, there was a significant correlation between SpA and IgG1 and IgG3 antibodies to human HSP60 but either weak or no correlation of SpA to antibodies to bacterial HSP60.…”

“…It was therefore concluded that while antibodies against human HSP60 are associated with SpA and are predominantly of the IgG3 subclass, antibodies against bacterial HSP60 are predominantly of the IgG1 subclass, indicating that there is no cross-reaction, and a role for anti-human HSP60 based on the ELISA results cannot support molecular mimicry as a pathogenic mechanism for arthritis diseases. The study by Hjelholt et al 21 showed in addition a weak correlation between anti-human HSP60 IgG3 and one of the several disease parameters. This was not seen in cohort study in which antibodies were determined over time comprising 48% of the samples analysed, probably due to the reduced number of patients participating in this study 21,22 .…”

“…The study by Hjelholt et al 21 showed in addition a weak correlation between anti-human HSP60 IgG3 and one of the several disease parameters. This was not seen in cohort study in which antibodies were determined over time comprising 48% of the samples analysed, probably due to the reduced number of patients participating in this study 21,22 . The association between elevated levels of antibodies against human HSP60 and SpA probably reflects a general activation of the immune system combined with increased appearance of human HSP60 outside inflammatory-associated damaged cells in the joints of patients with SpA.…”

“…The use of a plasmid (pRSET) that contained a 4.5 kDa fusion peptide with a polyhistidine tail made it possible to produce a pure recombinant protein using metal ion (Ni 2+ ) affinity chromatography. By generating specific antisera in rabbits towards probability-selected 21 Axial SpA Gelsing Carlsen et al 22 AS, Ankolysing spondylitis; CD, Chron's disease; Mb, mycobacterial; Ra, rheumatoid arthritis; ReA, reactive arthritis; SpA, spondylo arthritis; SLE, systemic lupus; TB, active tuberculosis; TFI, tubal factor infertility; UC, ulcerative colitis.…”