title: Evaluation of antibodies against human HSP60 in patients with MPO-ANCA associated glomerulonephritis: a cohort study.
abstract: BACKGROUND
  Human Heat Shock Protein 60 (hHSP60) has been implicated in autoimmunity through molecular mimicry, based on the high degree of homology with HSP65 of micro-organisms leading to autoimmune recognition of the human protein. Additionally, sequence homology between hHSP60 and myeloperoxidase (MPO) has been described. MPO is a major autoantigen in vasculitis associated with antineutrophil cytoplasmic antibodies (ANCA). We hypothesized that infections may trigger the ANCA response against MPO through hHSP60.
  
  
  METHODS
  In 86 consecutive patients with ANCA-associated vasculitis (AAV), anti-hHSP60 and anti-mycobacterial HSP65 were measured by ELISA. Patients were compared with 69 healthy controls (HC). Continuous data between groups were compared using Wilcoxon signed rank test and Kruskal-Wallis test with Dunn's post-test when appropriate. Correlations between data were derived using Spearman correlation. Odds ratios and 95% confidence intervals were obtained using Fisher's exact test.
  
  
  RESULTS
  At diagnosis, median anti-mHSP65 level was higher in AAV (median [range]: 42.5 [0-500]), and subsequently in MPO-ANCA (44 [7-500]), compared to HC (22 [0-430]). Anti-hHSP60 levels in AAV were not higher compared to HC (18 [0-319] and 18.5 [0-98], respectively). However, in MPO-ANCA anti-hHSP60 levels were increased (32.5 [0-319]) compared to PR3-ANCA (13 [0-79]) and HC. We could not detect cross-reactivity between hHSP60 and MPO-ANCA. There was a correlation between anti-mHSP65 and anti-hHSP60 levels (r = 0.32, P = 0.003) but not between anti-hHSP60 and MPO-ANCA (r = -0.064, P = 0.69).
  
  
  CONCLUSIONS
  Antibodies against mHSP65 are higher in AAV compared to HC, and anti-hHSP60 antibodies are higher in patients with MPO-ANCA than in patients with PR3-ANCA and HC. Although this finding may be indicative for cross-reactivity between MPO-ANCA and hHSP60, additional assays did not support this hypothesis.
authors: Dept, of Clinical and Experimental Immunology, University Hospital Maastricht, P,O, Box 5800, 6202 AZ Maastricht, The Netherlands. m.slot@immuno.unimaas.nl
authors: Marjan C
authors: MC
authors: Slot
authors: Ruud
authors: R
authors: Theunissen
authors: Pieter
authors: P
authors: van Paassen
authors: Jan G M C
authors: JG
authors: Damoiseaux
authors: Jan Willem Cohen
authors: JW
authors: Tervaert