New research on the autoimmune disease systemic lupus erythematosus (SLE) provides hints to the origins of the puzzling disorder.
The results were published Monday in Nature Immunology.
In people with SLE, their B cells – part of the immune system – are abnormally activated.
That makes them produce antibodies that react against their own tissues, causing a variety of symptoms, such as fatigue, joint pain, skin rashes, and kidney problems.
Scientists at Emory University School of Medicine could discern that in people with SLE, signals driving expansion and activation are present at an earlier stage of B cell differentiation than previously appreciated.
They identified patterns of gene activity that could be used as biomarkers for disease development.
“Our data indicate a disease signature across all cell subsets, and importantly on mature resting B cells, suggesting that such cells may have been exposed to disease-inducing signals,” the authors write.
The paper reflects a collaboration between the laboratories of Jeremy Boss, PhD, chairman of microbiology and immunology, and Ignacio (Iñaki) Sanz, MD, head of the division of rheumatology in the Department of Medicine. Sanz, recipient of the 2019 Lupus Insight Prize from the Lupus Research Alliance, is director of the Lowance Center for Human Immunology and a Georgia Research Alliance Eminent Scholar.
The first author is Christopher Scharer, PhD, assistant professor of microbiology and immunology.
Emory research on the autoimmune disease systemic lupus erythematosus (SLE) provides hints to the origins of the puzzling disorder. The image is credited to Emory University.
The researchers studied blood samples from 9 African American women with SLE and 12 healthy controls.
They first sorted the B cells into subsets, and then looked at the DNA in the women’s B cells, analyzing the patterns of gene activity.
Sanz’s team had previously observed that people with SLE have an expansion of “activated naïve” and DN2 B cells, especially during flares, periods when their symptoms are worse.
By examining epigenetic parameters – inherited traits not encoded in the DNA sequence – and patterns of gene activity, the researchers could see signs of activation in “resting naïve” B cells, which precede the activated naïve cells.
They were able to surmise that resting naïve cells are being stimulated through particular receptor pathways.
This “provides an important window to understand early antigenic triggers,” the authors write.
The authors were also able to identify regulatory networks that drive the disease phenotype in SLE B cells.
Together, these their results open up new avenues for future investigation and therapeutic interventions.
Funding: The research was supported by the National Institute of Allergy and Infectious Diseases (U19AI110483, P01AI125180, RO1AI113021, F31AI112261) and the National Institute of General Medical Sciences (T32GM008490).
Back in 1987, Klinman and Steinberg1 used an ELISpot assay to claim that systemic autoimmune diseases arise from polyclonal B-cell activation.
They recorded that B cells producing antibodies against nominal antigens or autoantigens were proportionally similar between healthy and lupus-prone mice and expanded en group in aging autoimmune mice.
The advent of B-cell receptor transgenic mice identified distinct autoantigen-specific tolerance breaks, which nicely explain the production of autoantibodies.
Additional sophisticated molecular studies have identified distinct checkpoints in B-cell development in which tolerance is broken and the expansion of autoreactive antibody-producing B/plasma cells becomes uncontrolled.2 Immunoglobulin sequencing studies in patients with systemic lupus erythematosus (SLE) and rheumatoid arthritis claimed defects at distinct checkpoints in early B-cell development to account for autoantibody production.3, 4
The question at hand is very important in shaping our approaches to treat autoimmune disease. Should tolerance be reinstated, or should the expansion of autoantibody-producing B/plasma cells be curtailed?
In this issue Suurmond et al5 used a simple assay to enumerate the presence of antinuclear antibody (ANA)–binding B cells in all developmental subsets of B cells in healthy and 2 lupus-prone strains of mice and in B cells from healthy subjects and patients with SLE. B-cell subsets, defined with the use of proper markers, that bind biotinylated nuclear material are easily recognized with fluoresceinated streptavidin.
Prior permeabilization of cells allowed for the recognition of ANA-positive plasma cells. First, the authors demonstrated the validity of the tool and showed that only ANA+ B cells (transitional [T] 2, follicular, and marginal zone cells) from healthy mice produce IgM autoantibodies recognizing, among others, double-stranded DNA, Sm, SS-A, and nucleosomes.
Using this tool, Suurmond et al5 demonstrated the increasing frequencies of ANA-binding B cells from premature to T2-like cells in the bone marrow and T1, T2, and T3 cells in the spleen, confirming the known positive selection during these phases. The assay cannot address events in pre–B-cell and immature B-cell subsets (do not express surface immunoglobulin) in which receptor editing and clonal deletion occur.
Similarly, this assay cannot assess avidity and affinity for nuclear antigens. Although it could address the role of apoptosis, which acts as a checkpoint process in the transitional phase, it cannot assess anergy, which again operates during the same phase.
The first interesting finding was recorded when Suurmond et al5 searched for ANA+ B cells in 2 lupus-prone mice.
Percentages of ANA+ B cells were comparable (even lower) in MRLlpr mice across all B-cell subsets, whereas greater percentages of ANA+ B cells noted in the T2, T3, and follicular B-cell subsets were recorded in NZB/W F1 mice.
Although both mouse strains serve as tools to study systemic autoimmunity, they use distinct pathways reflecting the molecular and cellular heterogeneity of patients with SLE.
In the human population the authors noted that a few patients had increased percentages of ANA+ naive B cells. It appears that some patients might behave like the NZB/W F1 mouse, in which an earlier check point is broken.
The exciting novel finding of this study is the observation that ANA intracellular positivity (plasma cells) decreases significantly in normal mice along with a significant decrease in IgG-switched B cells and IgG+ plasma cells.
In contrast, there was an expansion of IgG+ switched cells and IgG+ plasmablasts, which was considered to be caused by increased B-cell activation6 and differentiation to IgG-producing plasma cells. It appears that lupus-prone mice lose the ability to contain IgG switching and differentiation into autoantibody-producing plasma cells.
Finally, study of human subjects revealed comparable processes. Percentage of ANA+ cells decreased from naive to memory IgG+ cells and to IgG+ plasma cells.
In the majority of patients with SLE, percentages of ANA+ B and plasma cells were comparable with those in healthy subsects. However, similar to the observations in lupus-prone mice, there was an increase in percentages of IgG+ plasma cells and a subsequent increase in total numbers of ANA+IgG+ plasma cells.
The data agree with those of a study of patients with active disease which used clonotype characterization approaches to demonstrate that unmutated antibody-producing cells are expanded during disease flares and arise from newly activated naive B cells.7
In simple terms ANA positivity exists in IgM+ and IgG+ switched B cells and IgM-producing plasma cells in equal percentages in both mice and human subjects with and without autoimmmune conditions, but they are precluded from becoming ANA+IgG+ plasma cells only in healthy mice and human subjects. This is the new checkpoint (Fig 1).
Fig 1
Distribution of ANA+ cells among various B-cell subsets and plasma cells. The y-axis is arbitrary. FO, Follicular; MZ, marginal zone; PC, plasma cells; T, transitional.View Large Image | View Hi-Res Image | Download PowerPoint Slide
What is the basis for this checkpoint? What enables ANA+IgG+ cells to expand? Although general immune stimulation frequently leads to hypergammaglobulinemia and autoantibody production, it is time limited and not typically linked to pathology.
Yet B-cell stimulators like BLyS alone in mice can lead to autoimmunity and organ inflammation.
If BLyS was a significant driver in this cell expansion, its blockade should have met more success, but this statement is qualified by the relative contribution of BLyS to ANA+IgG+ cell expansion and the possibility that the BLyS pathway might be irrelevant in the expression of disease in a significant number of patients.
B cells from patients with SLE display a number of molecular abnormalities, including aberrant expression of kinases and phosphatases8 which are expressed variably in different patients and they can contribute to the malfunction of this new checkpoint.
An IgG1 single nucleotide polymorphism linked to the expression of SLE was found to instigate lupus when knocked in in mice by potentiating the signaling process on antigen binding.9
In addition, it is possible that this checkpoint is under the control of regulatory T cells and is amenable to correction by boosting the weak regulatory T-cell function in patients with SLE.10
Additional information on the behavior of the new checkpoint in patients treated with anti-BLyS or cytotoxic drugs that may block the expansion of ANA+IgG+ cells would be helpful. Similarly, use of this new assay to study patients during and after an infection, during which Toll-like receptors that contribute to B-cell autoimmunity8 can be engaged and expand B cells, can support the concept that autoimmunity results from expansion of existing autoreactive B cells.
Use of the reported assay to determine the behavior of the checkpoint during disease flares and whether it is re-established when the disease remits would also be informative.
Do the findings of this study override previous knowledge on control of B-cell autoimmunity? Or, more appropriately, how does the existence of the new checkpoint that limits the generation of ANA+IgG+ plasma cells complement previous knowledge. The authors have discussed in a comprehensive manner previous knowledge on events that are known to silence B-cell autoimmunity.
Given that one lupus mouse strain and a few patients with SLE display increased ANA reactivity in early B-cell subsets, it is certain that the new checkpoint is not exclusive in all patients with SLE.
It is probable that the presented expansion of existing autoreactive B cells accounts for the expression of autoimmunity in a number of patients, whereas one or more of the well-established immune tolerance checkpoints operate in other patients, which brings up the issue of the pathogenetic heterogeneity of patients with SLE and the need to tackle, should tools become available, the distinct abnormality that accounts for the expression of autoimmunity and disease in each patient.
The presented assay itself should allow us to determine which therapeutic interventions affect the generation of ANA IgG+ plasma cells and in which patients.
References
- Klinman, D.M. and Steinberg, A.D. Systemic autoimmune disease arises from polyclonal B cell activation. J Exp Med. 1987; 165: 1755–1760
- Li, H., Jiang, Y., Prak, E.L., Radic, M., and Weigert, M. Editors and editing of anti-DNA receptors.Immunity. 2001; 15: 947–957
- Yurasov, S., Wardemann, H., Hammersen, J., Tsuiji, M., Meffre, E., Pascual, V. et al. Defective B cell tolerance checkpoints in systemic lupus erythematosus. J Exp Med. 2005; 201: 703–711
- Samuels, J., Ng, Y.S., Coupillaud, C., Paget, D., and Meffre, E. Impaired early B cell tolerance in patients with rheumatoid arthritis. J Exp Med. 2005; 201: 1659–1667
- Suurmond, J., Atisha-Fregoso, Y., Marasco, E., Barlev, A.N., Ahmed, N., Calderon, S.A. et al. Loss of an IgG plasma cell checkpoint in patients with lupus. J Allergy Clin Immunol. 2019; 143: 1586–1597
- Liossis, S.N., Kovacs, B., Dennis, G., Kammer, G.M., and Tsokos, G.C. B cells from patients with systemic lupus erythematosus display abnormal antigen receptor-mediated early signal transduction events. J Clin Invest. 1996; 98: 2549–2557
- Tipton, C.M., Fucile, C.F., Darce, J., Chida, A., Ichikawa, T., Gregoretti, I. et al. Diversity, cellular origin and autoreactivity of antibody-secreting cell population expansions in acute systemic lupus erythematosus. Nat Immunol. 2015; 16: 755–765
- Dorner, T., Jacobi, A.M., and Lipsky, P.E. B cells in autoimmunity. Arthritis Res Ther. 2009; 11: 247
- Chen, X., Sun, X., Yang, W., Yang, B., Zhao, X., Chen, S. et al. An autoimmune disease variant of IgG1 modulates B cell activation and differentiation. Science. 2018; 362: 700–705
- Sharabi, A., Tsokos, M.G., Ding, Y., Malek, T.R., Klatzmann, D., and Tsokos, G.C. Regulatory T cells in the treatment of disease. ([Epub ahead of print])Nat Rev Drug Discov. 2018;
Source:
Emory University
Media Contacts:
Quinn Eastman – Emory University
Image Source:
The image is credited to Emory University.
Original Research: Closed access
“Epigenetic programming underpins B cell dysfunction in human SLE”. Christopher D. Scharer, Emily L. Blalock, Tian Mi, Benjamin G. Barwick, Scott A. Jenks, Tsuneo Deguchi, Kevin S. Cashman, Bridget E. Neary, Dillon G. Patterson, Sakeenah L. Hicks, Arezou Khosroshahi, F. Eun-Hyung Lee, Chungwen Wei, Iñaki Sanz & Jeremy M. Bos.
Nature Immunology. doi:10.1038/s41590-019-0419-9
