High Prevalence of Autoantibodies to hLAMP-2 in Anti–Neutrophil Cytoplasmic Antibody–Associated Vasculitis

Abstract

The involvement of autoantibodies to human lysosome-associated membrane protein-2 (hLAMP-2) in anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis is controversial because of the absence of confirmatory data subsequent to the initial reports of their high prevalence in this disease. We characterized three assays for anti-hLAMP-2 antibodies: ELISA and Western blotting assays using unglycosylated recombinant hLAMP-2 expressed in Escherichia coli, and an indirect immunofluorescence assay using stably transfected ldlD cells that expressed glycosylated full-length hLAMP-2 on the plasma membrane. The assays detected autoantibodies to hLAMP-2 in human sera reproducibly and with comparable sensitivity and the assays gave the same results in 80.5% of the test panel of 40 selected positive and negative sera. In untreated patients at presentation, the frequencies of autoantibodies to LAMP-2 were 89%, 91%, and 80%, respectively, among three groups of patients with ANCA-associated vasculitis from Vienna, Austria (n=19); Groningen, the Netherlands (n=50) and Cambridge, United Kingdom (n=53). Prevalence of LAMP-2 autoantibodies was similar in both those with myeloperoxidase-ANCA and proteinase 3-ANCA. Furthermore, we detected LAMP-2 autoantibodies in two ANCA-negative patients. LAMP-2 autoantibodies rapidly became undetectable after the initiation of immunosuppressive treatment and frequently became detectable again during clinical relapse. We conclude that when robust assays are used, circulating autoantibodies to hLAMP-2 can be detected in most European patients with ANCA-associated vasculitis. Large-scale prospective studies are now needed to determine whether they are pathogenic or merely an epiphenomenon.

Anti–LAMP-2 Autoantibodies in ANCA-Associated Pauci-Immune Glomerulonephritis

“…Although this finding fails to achieve statistical significance, it provides a hint that population differences may contribute to the discordant findings. However, even in this subset, the prevalence of anti-LAMP-2 remains substantially lower than the prevalence reported in the work by Kain et al, 9 suggesting that additional factors are also involved.…”

“…A consistent feature of the studies by Kain et al 6,9 has been that the highest anti-LAMP-2 antibody prevalence is in patients presenting with an untreated, active glomerulonephritis. Moreover, they found that anti-LAMP-2 titers are remarkably sensitive to disease activity and/or immunosuppression to the extent that, in their current report, Kain et al…”

“…Using three independent assays (ELISA, Western blot, and immunofluorescence), they report an overall frequency of 81% in patients presenting with an ANCA-associated glomerulonephritis, significantly higher than healthy controls and two sets of disease controls, one with a range of non-ANCA-associated renal diseases and another with active systemic lupus erythematosus. 9 Together, these findings represent data from an additional 74 patients with untreated, new-onset ANCA-associated disease and 52 patients with treated ANCA-associated disease either during a flare or in remission. 9 The discordance between these two studies is concerning, and reconciling them will be critical to determining the role of anti-LAMP-2 antibodies in the pathogenesis and clinical management of ANCA-associated vasculitis.…”

“…9 Together, these findings represent data from an additional 74 patients with untreated, new-onset ANCA-associated disease and 52 patients with treated ANCA-associated disease either during a flare or in remission. 9 The discordance between these two studies is concerning, and reconciling them will be critical to determining the role of anti-LAMP-2 antibodies in the pathogenesis and clinical management of ANCA-associated vasculitis.…”

“…8 None of these rats went on to develop clinical or histologic glomerulonephritis. 8 In contrast, JASN also contains a report by Kain et al 9 in which their initial findings of high anti-LAMP-2 antibody prevalence in ANCA-associated glomerulonephritis are recapitulated in additional cohorts drawn from three European centers: Vienna, Groningen, and Cambridge. Using three independent assays (ELISA, Western blot, and immunofluorescence), they report an overall frequency of 81% in patients presenting with an ANCA-associated glomerulonephritis, significantly higher than healthy controls and two sets of disease controls, one with a range of non-ANCA-associated renal diseases and another with active systemic lupus erythematosus.…”