ABSTRACT
BACKGROUND: Anti-neutrophil cytoplasmic antibodies (ANCA) directed against proteinase 3 (PR3-ANCA) are a serological hallmark of small vessel vasculitis, particularly granulomatosis with polyangiitis (GPA). To increase their sensitivity, some ELISA employ the human native PR3 combined with a recombinant protein. Their specificity in daily practice is still to be defined. Our objective was to compare the performance for GPA diagnosis of three PR3-ANCA assays in daily practice. PATIENTS AND METHODS: Seventy-eight consecutive patients' sera with suggestive IIF were included. All sera were tested with a routine Enzyme Linked Immuno adsorbant Assay (ELISA) employing a mixture of human native and human recombinant (hn+hr) PR3 (EUROIMMUN™) compared to two assays using immobilized purified human PR3 (QUANTA Lite(®) ELISA and QUANTA Flash(®) Chemiluminescence assay (CIA), INOVA Diagnostics). Clinical data including BVAS score were collected retrospectively. RESULTS: Nineteen out of the 78 patients had GPA. The hn+hr PR3 ELISA had a good sensitivity (100%) but a lower specificity for the diagnosis of GPA (61.0%) than the assays using the sole native protein (hn ELISA: 81.4%, hn CIA: 69.5%). False positive results mainly consisted of patients with inflammatory bowel disease, who had a specific PR3-ANCA positivity assembly when coupling the assays. The antibody titers by human native PR3 assays, but not hn+hr assay, positively correlated with BVAS score. CONCLUSION: These results highlight the need of a close collaboration between physicians and immunologists. Combining assays including last generation CIA employing human native antigens should improve the performance of GPA's diagnosis.
Subject(s)
Antibodies, Antineutrophil Cytoplasmic/blood , Enzyme-Linked Immunosorbent Assay/methods , Granulomatosis with Polyangiitis/diagnosis , Granulomatosis with Polyangiitis/blood , Granulomatosis with Polyangiitis/immunology , Humans , Luminescent Measurements , Middle Aged , Myeloblastin/metabolism , Recombinant Proteins/metabolism , Sensitivity and Specificity , Vasculitis/blood , Vasculitis/diagnosis , Vasculitis/immunologyABSTRACT
The molecular markers that distinguish primary mediastinal large B-cell lymphoma (PMBL) from nonmediastinal diffuse large B-cell lymphomas (NM-DLBLs) remain to be identified. Using cDNA representational difference analysis to compare PMBL and NM-DLBL transcripts, we isolated a cDNA fragment homologous to the mouse B-cell interleukin 4 (IL-4)-inducible gene FIG1 (interleukin 4-induced gene 1) transcript. The human FIG1 mRNA encodes a 567 amino acid protein that comprises a signal peptide and a large flavin-binding amino oxidase domain, and shares significant homology with secreted apoptosis-inducing L-amino acid oxidases. Northern blot studies showed that FIG1 mRNA expression is mainly restricted to lymphoid tissues. It is expressed at low levels in thymus, spleen, tonsils, and reactive lymph nodes, and is highly up-regulated in IL-4+CD40-activated tonsillar B cells. Interestingly, in human B-cell lines, FIG1 mRNA expression appeared restricted to the PMBL-derived MedB-1 and Karpas 1106 cell lines. Using real-time reverse transcriptase-polymerase chain reaction (RT-PCR), we demonstrated that all but one PMBL (16/17) displayed high FIG1 mRNA levels, whereas most NM-DLBLs (12/18) and all low-grade B-cell lymphomas tested (8/8) exhibited low FIG1 mRNA levels. The difference between PMBLs and NM-DLBLs was statistically significant (Fisher test; P =.0003). Southern blot studies did not show rearrangement of the FIG1 gene. FIG1 gene expression might be due to a constitutive activation of a cytokine signaling pathway in PMBL.
