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Objectives To explore the applicability of chip-cytometry for spatial proteomics allowing the phenotypical characterization of tubulointerstitial inflammatory infiltrates in lupus nephritis (LN).Methods Four paraffin embedded kidney biopsies, from three LN patients were selected for this study. Two samples belonged to a single patient (pre-/post- induction therapy). The samples were chosen based the presence of inflammatory infiltrates. For chip cytometry, tissue was deparaffinized, rehydrated and underwent heat-mediated antigen retrieval. After checking the autofluorescence level, the tissue was stained in repeated cycles with monoclonal antibodies (four per cycle) for immunophenotyping and high-range images were obtained and overlayed according to standard prototol for CellScape™ equipment. Images were processed in QuPath and segmented with StarDist extension to obtain cell counts. A threshold was set to classify all detected cells as positive or negative for each marker. A total panel of 16 markers was used to identify cells of the T-, B- and myeloid cell lines. Values are given as median percentages of single cell types.Results Tissue integrity and quality staining was good to acceptable across the studied biopsies, which presented a broad range of total cellularity and cell density. Overall (figure1), T cells (CD54+CD3+CD56-) were more abundant than B cells (CD45+CD3-CD56-CD20+), median 32.2% vs 1.5%. CD8+ presumably cytotoxic cells (CD45+, CD3+, CD56-, CD4-, CD8+) were more abundant than CD4+T helper cells (CD45+, CD3+, CD56-, CD4+, CD8-), median 38.1 vs 23.1% of total T cells. The most abundant CD8+ subphenotype was effector memory (CD45+CD3+CD56-CD4-, CD8+CD45RA-CD27-), median 74.8%, same for CD4+ T cells (CD45+, CD3+, CD56-, CD4+, CD8-, CD45RA-, CD27- ), median 73%. When dissecting B cell subphenotypes, these were mostly naïve CD45+CD3-CD56-CD20+CD27- (median 88%), while memory B cells CD45+CD3-CD56-CD20+CD27+ were less represented (median 9.2%). One biopsy lacked B cells; the patient had received rituximab 9 months previously. In pre- and post- treatment samples infiltrating cells persisted.Abstract PO:09:244 Figure 1Conclusions Chip-cytometry is feasible on paraffin preserved LN kidney biopsy samples and is a potential tool to dissect the complexity of immune cell infiltration in LN which might complement standard histopathology and help inform the risk of future relapse.