[Immunodiagnostic and immunopathogenetic significance of anti-neutrophil cytoplasma antibodies]

Anticytokeratins are a potential source of false-positive indirect immunofluorescence assays for C-ANCA

Antibodies to neutrophil cytoplasmic antigens (ANCA) targeted toward granule enzymes have been recognized as a valuable diagnostic tool in the detection of Wegener's granulomatosis and systemic vasculitides. However, the most commonly used method of detection, the indirect immunofluorescence assay, is prone to false-positive results due to antibodies of different pathological significance either targeted to, or cross-reacting with, similarly distributed epitopes. Using double immunofluorescence, the present study demonstrates that anticytokeratin antibodies are able to produce false-positive C-ANCA immunofluorescence assays. In addition, a case of natural appearance of cytokeratin-reactive antibodies causing a false-positive "pseudo-ANCA" staining pattern in a patient presenting with sepsis is reported. Since the expression of cytokeratins is almost exclusively confined to epithelial cells, the most plausible explanation for both phenomena is a crossreaction of anticytokeratin antibodies with granule associated epitopes. Due to the natural appearance of anticytokeratin antibodies in association with a variety of other pathologic entities, it is of crucial importance for the diagnostic significance of the C-ANCA immunofluorescence assay to exclude anticytokeratin caused false-positive results. It is shown that supplementary indirect immunofluorescence tests performed on cultured human epithelial cells readily distinguish anticytokeratin caused "pseudo-ANCA" from true C-ANCA.

Indirect immunofluorescence study of the cornea and the conjunctiva in a xenogeneic system: analysis of humoral reactivity in patients with Wegener's granulomatosis

BACKGROUND

Ocular involvement in patients with Wegener's granulomatosis (WG) can cause progressive loss of vision. The pathophysiological events leading to the WG-specific ocular inflammation are unknown.

METHODS

A method involving indirect immunofluorescence on bovine and porcine corneoconjunctival frozen sections was used to detect antibodies to corneal and conjunctival epithelium in serum samples from patients suffering from WG with ophthalmic involvement (orbital granuloma or ocular vasculitis, both active and inactive phase). Normal persons and WG patients without ophthalmic involvement served as control groups. Anti-human IgG, IgA and IgM were tested.

RESULTS

Five different immunofluorescence patterns could be distinguished in each species. There were differences in the reactivity with bovine and porcine tissue. Every pattern was caused mainly by human IgG. The antibodies were directed to the cell nuclei or to extranuclear structures. All patterns also occurred frequently in normal sera. No pattern was found that occurred specifically in the serum of patients with WG and ocular inflammation.

CONCLUSIONS

The results indicate that this immunofluorescence system does not detect a characteristic antibody profile that could be attributed to the serum of WG patients. Hence the approach lacks clinical usefulness as a diagnostic procedure.