Autoantibodies directed against labile epitopes on cell surface proteins in autoimmune disease patients: Proposal of a novel ELISA for the detection of anti-endothelial cell antibodies

Detection of subtype-specific breast cancer surface protein biomarkers via a novel transcriptomics approach

BACKGROUND

Cell-surface proteins have been widely used as diagnostic and prognostic markers in cancer research and as targets for the development of anticancer agents. So far, very few attempts have been made to characterize the surfaceome of patients with breast cancer, particularly in relation with the current molecular breast cancer (BRCA) classification. In this view, we developed a new computational method to infer cell-surface protein activities from transcriptomics data, termed 'SURFACER'.

METHODS

Gene expression data from GTEx were used to build a normal breast network model as input to infer differential cell-surface proteins activity in BRCA tissue samples retrieved from TCGA versus normal samples. Data were stratified according to the PAM50 transcriptional subtypes (Luminal A, Luminal B, HER2 and Basal), while unsupervised clustering techniques were applied to define BRCA subtypes according to cell-surface proteins activity.

RESULTS

Our approach led to the identification of 213 PAM50 subtypes-specific deregulated surface genes and the definition of five BRCA subtypes, whose prognostic value was assessed by survival analysis, identifying a cell-surface activity configuration at increased risk. The value of the SURFACER method in BRCA genotyping was tested by evaluating the performance of 11 different machine learning classification algorithms.

CONCLUSIONS

BRCA patients can be stratified into five surface activity-specific groups having the potential to identify subtype-specific actionable targets to design tailored targeted therapies or for diagnostic purposes. SURFACER-defined subtypes show also a prognostic value, identifying surface-activity profiles at higher risk.

Isolation of human monoclonal antibodies that bind to two different antigens and are encoded by germline VH and VL genes

This paper reports isolation of two monoclonal antibodies (mAbs) that bind to both a membrane protein and a cytoplasmic protein. Most Abs established as markers for autoimmune disease bind to cytoplasmic or nuclear substances. However, it remains unknown how these Abs are produced. On the other hand, there were examples where clones originally isolated as Abs that bind to membrane proteins also showed binding activity to cytoplasmic or nuclear substances. Based on these results, the following hypothesis has been proposed. The Abs that had been originally produced against a membrane protein showed cross-reactivity against cytoplasmic or nuclear substances. In the present study we reported isolation of Abs that bound to both a membrane protein, CADM1, and a cytoplasmic protein, α-actinin-4. The method adopted in the present study could be generally applicable to isolation of Abs showing such dual specificity. Firstly, we constructed a huge human Ab library using various organs including naïve B-cell-rich organs such as bone marrow and umbilical cords. Then, we developed a comprehensive screening method for isolation of Abs that bound to cell surface antigens. Through extensive screenings with many kinds of cell we newly obtained a library composed of around 4000 independent clones that bind to membrane proteins. We screened this library with α-actinin-4 and succeeded in isolating two Abs. They bound to α-actinin-4 and a membrane protein CADM1. Furthermore, they are encoded by naïve heavy and light chain variable genes (V_H & V_L). These results suggested that cross-reactive Abs to both a membrane protein and a cytoplasmic protein could be present in germline repertoire of Ab in humans. This methodology adopted in the present study could be applied to isolation of cross-reactive Abs possibly involved in autoimmune diseases.

From microvasculature to fibroblasts: Contribution of anti-endothelial cell antibodies in systemic sclerosis

Systemic sclerosis (SSc) is an autoimmune disease characterized by skin and internal organ fibrosis, caused by microvascular dysfunction. In recent years, the hypothesis that anti-endothelial cell antibodies (AECA) play a key role in microvascular damage seems to be increasingly convincing. In fact, AECA can induce antibody-dependent cellular apoptosis and stimulate the microvasculature to release pro-inflammatory and pro-fibrotic cytokines. Human-microvascular-endothelial-cells (MVECs) were stimulated with SSc sera (with and without AECA) and with sera from healthy donors. The conditioned MVEC culture media were then added to fibroblast cultures obtained from control skin (CTR), non-affected skin of SSc patients (NA), and affected skin of the same sclerodermic (SSc) patients, respectively. AECA contributed to the MVEC increased release of endothelin-1 (ET-1) in the culture medium and to MVEC apoptosis. Fibroblast (CTR, NA, and SSc) proliferation was increased after treatment with AECA-positive conditioned media, compared to AECA-negative and control conditioned media. Furthermore, both AECA-positive (in major contribution) and AECA-negative conditioned media were responsible for alpha-smooth-muscle-actin (αSMA) over-expression in all fibroblast cultures, compared to control conditioned media. Fibroblast type I collagen synthesis was upregulated by both SSc conditioned media (with and without AECA). Finally, the synthesis of fibroblast transforming-growth-factor-beta (TGF-β) was statistically higher in AECA-positive conditioned media, compared to AECA-negative and control conditioned media. These findings support the concept that AECA may mediate the crosstalk between endothelial damage and dermal-fibroblast activation in SSc.

The Level of IgA Antibodies to Endothelial Cells Correlates with Histological Evidence of Disease Activity in Patients with Lupus Nephritis

Anti-endothelial cell antibodies (AECA) are frequently detected in patients with systemic lupus erythematosus (SLE), but their pathological role remains unclear. We recently developed a solubilized cell surface protein capture enzyme-linked immunosorbent assay (CSP-ELISA) to detect antibodies against membrane proteins involved in autoimmune reactions. In this study, sera from 51 patients with biopsy-proven lupus nephritis (LN), 25 with SLE without renal involvement (non-LN SLE), 42 disease control (DC) subjects, and 80 healthy control (HC) subjects were tested for IgG- and IgA-AECA for human umbilical vein endothelial cells (HUVEC) and human glomerular EC (HGEC) by using CSP-ELISA. IgG- and IgA-AECA titers were significantly higher in LN and non-LN SLE patients than in the DC or HC (P < 0.001) groups. IgG- and IgA-AECA titers for HUVEC corresponded well with those for HGEC. The IgA-AECA level correlated with the SLE disease activity index and with histological evidence of active lesions (cellular proliferations, hyaline thrombi and wire loops, leukocytic infiltration, and fibrinoid necrosis) in LN patients (P < 0.001). The sensitivity of IgA-AECA as a diagnostic test for histological evidence of active lesions in LN patients was 0.92, with a specificity of 0.70. The significant correlation of IgA-AECA with glomerular hypercellularity indicates that IgA-AECA are associated with endothelial damage in LN.

Isolated De Novo Antiendothelial Cell Antibodies and Kidney Transplant Rejection

BACKGROUND

Studies analyzing the role of antiendothelial cell antibodies (AECAs) in large series of kidney transplant recipients are scarce, and HLA, MHC (major histocompatibility complex) class I-related chain A (MICA), and angiotensin II type 1 receptor have not been formally excluded as targets.

STUDY DESIGN

Retrospective study of a cohort of kidney transplant recipients.

SETTING & PARTICIPANTS

324 kidney transplant recipients who were negative for anti-HLA, anti-MICA, and anti-angiotensin II type 1 receptor antibodies were tested for AECAs in pre- and posttransplantation serum samples.

PREDICTORS

AECA-positive (preformed [pre⁺/post⁺] vs de novo [pre^-/post⁺]) versus AECA-negative (pre^-/post^-) before or after transplantation.

OUTCOMES

Patient mortality, transplant loss, and acute rejection events.

RESULTS

66 (20%) patients were AECA positive (39 [12%] preformed, 27 [8%] de novo) and 258 (80%) were AECA negative. During a follow-up of 10 years, 7 (18%) AECA pre⁺/post⁺ patients had rejections compared with 14 (52%) AECA pre^-/post⁺ and 57 (22%) AECA pre^-/post^- recipients (OR, 3.80; P=0.001). AECA pre^-/post⁺ status emerged as an independent risk factor for transplant rejection compared to the AECA pre^-/post^- group (OR, 5.17; P<0.001). However, AECA pre⁺/post⁺ and AECA pre^-/post⁺ patients did not show higher risk for either patient death (ORs of 1.49 [P=0.7] and 1.06 [P=0.9], respectively) or transplant loss (ORs of 1.22 and 0.86, respectively; P for both = 0.8) compared to the AECA pre^-/post^- population.

LIMITATIONS

Retrospective study. Posttransplantation sera were collected before or after rejection, entailing a nearly cross-sectional relationship between the exposure and outcome. Lack of identification of precise antigens for AECAs.

CONCLUSIONS

De novo AECAs may be associated with rejection. These antibodies might serve as biomarkers of endothelium damage in kidney transplant recipients.

An innovative method to identify autoantigens expressed on the endothelial cell surface: serological identification system for autoantigens using a retroviral vector and flow cytometry (SARF)

Autoantibodies against integral membrane proteins are usually pathogenic. Although anti-endothelial cell antibodies (AECAs) are considered to be critical, especially for vascular lesions in collagen diseases, most molecules identified as autoantigens for AECAs are localized within the cell and not expressed on the cell surface. For identification of autoantigens, proteomics and expression library analyses have been performed for many years with some success. To specifically target cell-surface molecules in identification of autoantigens, we constructed a serological identification system for autoantigens using a retroviral vector and flow cytometry (SARF). Here, we present an overview of recent research in AECAs and their target molecules and discuss the principle and the application of SARF. Using SARF, we successfully identified three different membrane proteins: fibronectin leucine-rich transmembrane protein 2 (FLRT2) from patients with systemic lupus erythematosus (SLE), intercellular adhesion molecule 1 (ICAM-1) from a patient with rheumatoid arthritis, and Pk (Gb3/CD77) from an SLE patient with hemolytic anemia, as targets for AECAs. SARF is useful for specific identification of autoantigens expressed on the cell surface, and identification of such interactions of the cell-surface autoantigens and pathogenic autoantibodies may enable the development of more specific intervention strategies in autoimmune diseases.