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.