Detecting autoreactive B cells in the peripheral blood of people with type 1 diabetes using ELISpot

Anti-dsDNA B-Cell ELISpot as a Monitoring and Flare Prediction Tool in SLE Patients

Anti-dsDNA autoantibodies quantification and complement levels are widely used to monitor disease activity in systemic lupus erythematosus (SLE). However, better biomarkers are still needed. We hypothesised whether the dsDNA antibody-secreting B-cells could be a complementary biomarker in disease activity and prognosis of SLE patients. Fifty-two SLE patients were enrolled and followed for up to 12 months. Additionally, 39 controls were included. An activity cut-off (comparing active and non-active patients according to clinical SLEDAI-2K) was established for SLE-ELISpot, chemiluminescence and Crithidia luciliae indirect immunofluorescence tests (≥11.24, ≥374.1 and ≥1, respectively). Assays performances together with complement status were compared regarding major organ involvement at the inclusion and flare-up risk prediction after follow-up. SLE-ELISpot showed the best performance in identifying active patients. High SLE-ELISpot results were associated with haematological involvement and, after follow-up, with an increased hazard ratio for disease flare-up (3.4) and especially renal flare (6.5). Additionally, the combination of hypocomplementemia and high SLE-ELISpot results increased those risks up to 5.2 and 32.9, respectively. SLE-ELISpot offers complementary information to anti-dsDNA autoantibodies to evaluate the risk of a flare-up in the following year. In some cases, adding SLE-ELISpot to the current follow-up protocol for SLE patients can improve clinicians' personalised care decisions.

Detection of Cytokine-Secreting Cells by Enzyme-Linked Immunospot (ELISpot)

The enzyme-linked immunospot (ELISpot) is a highly sensitive immunoassay that measures the frequency of cytokine-secreting cells at the single-cell level. The secreted molecules are detected by using a detection antibody system similar to that used in the enzyme-linked immunosorbent assay (ELISA). The ELISpot assay is carried out in a 96-well plate and an automated ELISpot reader is used for analysis. The assay is easy to perform, robust and allows rapid analysis of a large number of samples and is not limited to measurement of cytokines; it is suitable for almost any secreted protein where single-cell analysis is of interest.

Detection and Enumeration of Cytokine-Secreting Cells by FluoroSpot

The FluoroSpot assay is a development of the highly sensitive enzyme-linked immunospot (ELISpot) assay which enables functional measurement of immunity at the single-cell level. Both assays are performed in a 96-well format and measures the frequency of analyte-secreting cells, in ELISpot usually limited to one analyte per well due to the use of enzymes and precipitating substrates for detection. FluoroSpot, performed in a similar way as ELISpot, overcomes this limitation by detecting each analyte with an assigned fluorophore instead of an enzyme. By using readers equipped with fluorophore-specific filters, cells producing single or multiple cytokines can be identified simultaneously in the same well. This greatly facilitates the analysis of functionally distinct subpopulations in heterogenous cell samples, for example, the frequency of polyfunctional T cells, suggested to be of importance in various disease states. FluoroSpot maintains the simplicity and sensitivity of the ELISpot while taking the assay a step further towards a multiplex analysis and an in-depth understanding of the quality of an immune response. We describe here a 96-well plate method to analyze cells that have secreted up to four different cytokines simultaneously (Four-color Fluorospot).

The Multiple Roles of B Lymphocytes in the Onset and Treatment of Type 1 Diabetes: Interactions between B Lymphocytes and T Cells

Although type 1 diabetes is thought to be an organ-specific autoimmune disease, mediated by effective CD4⁺ and CD8⁺ T cells, it has recently become clear that B cells participate in the initiation and progress of this disease. Indeed, B cell deletion can prevent or reverse autoimmune diabetes in nonobese diabetic mice and even result in partially remaining β cell function in patients with new-onset type 1 diabetes. This review summarizes the dual role of B cells in this process not only of pathogenic effect but also of immunoregulatory function in type 1 diabetes. We focus on the impact that B cells have on regulating the activation, proliferation, and cytokine production of self-reactive T cells along with regulatory T cells, with the aim of providing a better understanding of the interactions between T and B cells in immunopathogenesis and improving the efficacy of interventions for clinical practice.

Slow progressors to type 1 diabetes lose islet autoantibodies over time, have few islet antigen-specific CD8+ T cells and exhibit a distinct CD95hi B cell phenotype

AIMS/HYPOTHESIS

The aim of this study was to characterise islet autoantibody profiles and immune cell phenotypes in slow progressors to type 1 diabetes.

METHODS

Immunological variables were compared across peripheral blood samples obtained from slow progressors to type 1 diabetes, individuals with newly diagnosed or long-standing type 1 diabetes, and healthy individuals. Polychromatic flow cytometry was used to characterise the phenotypic attributes of B and T cells. Islet autoantigen-specific B cells were quantified using an enzyme-linked immunospot (ELISpot) assay and islet autoantigen-specific CD8⁺ T cells were quantified using peptide-HLA class I tetramers. Radioimmunoassays were used to detect islet autoantibodies. Sera were assayed for various chemokines, cytokines and soluble receptors via ELISAs.

RESULTS

Islet autoantibodies were lost over time in slow progressors. Various B cell subsets expressed higher levels of CD95 in slow progressors, especially after polyclonal stimulation, compared with the corresponding B cell subsets in healthy donors (p < 0.05). The phenotypic characteristics of CD4⁺ and CD8⁺ T cells were similar in slow progressors and healthy donors. Lower frequencies of CD4⁺ T cells with a central memory phenotype (CD27^int, CD127⁺, CD95^int) were observed in slow progressors compared with healthy donors (mean percentage of total CD4⁺ T cells was 3.00% in slow progressors vs 4.67% in healthy donors, p < 0.05). Autoreactive B cell responses to proinsulin were detected at higher frequencies in slow progressors compared with healthy donors (median no. of spots was 0 in healthy donors vs 24.34 in slow progressors, p < 0.05) in an ELISpot assay. Islet autoantigen-specific CD8⁺ T cell responses were largely absent in slow progressors and healthy donors. Serum levels of DcR3, the decoy receptor for CD95L, were elevated in slow progressors compared with healthy donors (median was 1087 pg/ml in slow progressors vs 651 pg/ml in healthy donors, p = 0.06).

CONCLUSIONS/INTERPRETATION

In this study, we found that slow progression to type 1 diabetes was associated with a loss of islet autoantibodies and a distinct B cell phenotype, consistent with enhanced apoptotic regulation of peripheral autoreactivity via CD95. These phenotypic changes warrant further studies in larger cohorts to determine their functional implications.