Kristine Oleinika

Systemic lupus erythematosus develops when autoreactive B cells escape tolerance and enter differentiation pathways that sustain pathogenic autoantibody responses. A defining feature of lupus is the evolving autoantibody repertoire, in which initially focused autoreactivity broadens over time through recruitment of additional self-reactive B cell clones as well as continued mutation and selection of B cells engaged in the response. Here, we review insights from the 564Igi lupus model, in which a defined autoreactive B cell clone creates an autoimmune environment that permits a previously tolerant polyclonal wild-type (WT) B cell repertoire to enter the response. Studies using mixed bone marrow chimera and adoptive transfer approaches show that WT-derived B cells can be recruited into established autoreactive niches, participate in germinal center and extrafollicular pathways, and contribute to epitope-spread autoantibody responses. We discuss how studies in the present model have reframed epitope spreading as a dynamic process of self-reactive B cell evolution, in which otherwise restrained B cells are incorporated into an ongoing autoimmune response and shaped by the niches that support their activation, differentiation, persistence, and diversification.

Chronic lymphocytic leukemia (CLL) is characterized by secondary immunodeficiency, yet the extent to which global disease-associated immune dysregulation impairs the ability to generate antigen-specific B cell immunity—independent of targeted therapy—remains unclear. To address this, we assessed the non-malignant B cell compartment and responses to SARS-CoV-2 vaccination in treatment-naive (CLL-TN) and chlorambucil-treated (CLL-CTx) patients. Despite marked alterations in peripheral B cell subsets, both CLL-TN and CLL-CTx patients exhibited higher absolute numbers of SARS-CoV-2 spike-specific B cells than healthy controls (HCs). The phenotypes of spike-specific B cells were also similar between groups, with most class-switched to IgG and only a small fraction displaying the IgD⁻CD27⁻ phenotype. Most patients also mounted robust anti-spike IgG responses with live virus neutralization comparable to HCs. Nevertheless, neutralization of certain Omicron subvariants was reduced in CLL patients compared with HCs, suggesting a selective constraint in response breadth. Together, these findings indicate that, in the context of SARS-CoV-2 vaccination, disease-associated immune dysregulation in CLL does not preclude effective B cell or antibody responses to SARS-CoV-2, although the breadth of these responses may be limited.

Systemic lupus erythematosus is characterized by activation of many self-reactive B cell clones that produce autoantibodies. This can be modeled using mixed bone marrow chimeras, where autoreactive 564Igi B cells initiate autoimmunity that spreads to wild-type (WT) B cells. The mechanisms controlling the inclusion of new B cell clones into spontaneous germinal centers (GCs) remain unclear. Using CRISPR-Cas9, we generated 2 autoreactive B cell receptor knock-in strains, M05 and G55, based on B cell receptors from WT GC B cells in WT:564Igi chimeras. M05 and G55 mice lacked spontaneous GCs and overt autoantibody production, with receptor editing (λ light chain expression) contributing to tolerance. However, autoreactivity was not purged from the B cell compartment since presence of 564Igi clone allowed M05 and G55 B cells to join GCs and produce autoantibodies. These findings reveal that GCs can override peripheral tolerance, recruiting previously silent autoreactive clones and facilitating diversification of autoantibodies.

Chronic lymphocytic leukemia (CLL) is associated with immune dysfunction, but how disease-intrinsic mechanisms in treatment-naive patients influence the coordination of adaptive responses to novel antigens remains unclear. Here, we assessed SARS-CoV-2-specific antibody and T cell immunity in 38 treatment-naive CLL patients and 13 healthy controls (HCs) following vaccination. Despite significantly reduced total immunoglobulin levels compared to HCs, 94.7% of CLL patients developed SARS-CoV-2-specific IgG, and 89.5% mounted IgA responses, with serum titers comparable to those of HCs. Virus-specific T cell responses, measured by IFN-γ release following antigen stimulation, were detected in 78.9% of patients. CLL patients had significantly more circulating CD4⁺ T follicular helper (Tfh) and T follicular regulatory (Tfr) cells than HCs. These expansions correlated with B cell abundance, which, in untreated CLL, predominantly reflects malignant B cells. Notably, Tfh cell frequencies and absolute counts were highest in patients lacking a SARS-CoV-2-specific T cell response, indicating a decoupling between Tfh expansion and functional antiviral immunity. Overall, these findings demonstrate that while SARS-CoV-2-specific immune responses are largely preserved in treatment-naive CLL patients, disease-driven alterations in T cell composition may compromise the coordination and quality of antigen-specific T cell-mediated immunity.

IgA nephropathy (IgAN) is characterised by the production of galactose-deficient IgA1 (GdIgA1) antibodies. As the source of pathogenic antibodies, B cells are central to IgAN pathogenesis, but the B cell activation pathways as well as the potential B cell source of dysregulated IgA-secretion remain unknown. We carried out flow cytometry analysis of peripheral blood B cells in patients with IgA nephropathy and control subjects with a focus on IgA-expressing B cells to uncover the pathways of B cell activation in IgAN and how these could give rise to pathogenic GdIgA1 antibodies. In addition to global changes in the B cell landscape – expansion of naive and reduction in memory B cells – IgAN patients present with an increased frequency of IgA-expressing B cells that lack the classical memory marker CD27, but are CD21^pos. IgAN patients further have an expanded population of IgA^pos antibody-secreting cells, which correlate with serum IgA levels. Both IgA^pos plasmabalsts and CD27^neg B cells co-express GdIgA1. Implicating dysregulation at mucosal surfaces as the driver of such B cell differentiation, we found a correlation between lipopolysaccharide (LPS) in the serum and IgA^posCD27^neg B cell frequency. We propose that dysregulated immunity in the mucosa may drive de novo B cell activation within germinal centres, giving rise to IgA^posCD27^neg B cells and subsequently IgA-producing plasmablasts. These data integrate B cells into the paradigm of IgAN pathogenesis and allow to further investigate this pathway to uncover biomarkers and develop therapeutic interventions.

Background: IgA nephropathy (IgAN) is characterised by the production of galactose-deficient IgA1 (Gd-IgA1) antibodies. As the source of pathogenic antibodies, B cells are central to IgAN pathogenesis, but the B cell activation pathways as well as the potential B cell source of dysregulated IgA-secretion remain unknown. Methods: We carried out flow cytometry analysis of peripheral blood B cells in patients with IgA nephropathy and control subjects with a focus on IgA-expressing B cells to uncover the pathways of B cell activation in IgAN and how these could give rise to pathogenic GdIgA1 antibodies. Results: In addition to global changes in the B cell landscape – expansion of naive and reduction in memory B cells – IgAN patients present with an increased frequency of IgA-expressing B cells that lack the classical memory marker CD27, but are CD21 ^pos . IgAN patients further have an expanded population of IgA ^pos antibody-secreting cells, which correlate with serum IgA levels. Both IgA ^pos plasmabalsts and CD27 ^neg B cells co-express GdIgA1. Implicating dysregulation at mucosal surfaces as the driver of such B cell differentiation, we found a correlation between lipopolysaccharide (LPS) in the serum and IgA ^pos CD27 ^neg B cell frequency. Conclusion: We propose that dysregulated immunity in the mucosa may drive de novo B cell activation within germinal centres, giving rise to IgA ^pos CD27 ^neg B cells and subsequently IgA-producing plasmablasts. These data integrate B cells into the paradigm of IgAN pathogenesis and allow to further investigate this pathway to uncover biomarkers and develop therapeutic interventions. Key learning points: What was known: Patients with IgA nephropathy (IgAN) have aberrant production of galactose-deficient IgA1 (Gd-IgA1) and antibodies against it, which together form immune complexes that are deposited in the renal mesangium and lead to kidney damage; this is known as the multi-hit model of IgAN pathogenesis. The multi-hit model centrally implicates B cells as they produce both Gd-IgA1 and antibodies against it, yet B cell activation pathways that lead to aberrant antibody production are absent from the model. Only isolated reports exist describing specific features of B cells that are altered in patients with IgAN, including a reduction in regulatory B cells, increase in toll-like receptor 7 expression in total peripheral blood B cells and elevated frequency of circulating CCR9 ⁺ IgA ⁺ B cells. This study adds: In addition to changes in the overall circulating B cell landscape, differentiation of IgA ⁺ plasmablasts is enhanced in patients with IgAN and their levels correlate with serum IgA. IgA-expressing plasmablast frequency correlates with that of IgA ⁺ CD21 ⁺ B cells, that lack the classical memory B cell marker CD27. Both IgA ⁺ plasmablasts and IgA-expressing CD27 ^- B cells co-express GdIgA1 receptors. IgA ⁺ CD27 ^- CD21 ⁺ B cell frequency correlates with serum lipopolysaccharide (LPS) levels, implicating mucosa in their activation. Potential impact: We uncover the previously unknown B cell activation pathway that appears to be associated with pathogenic IgA secretion in IgAN and integrate this into the multi-hit model of IgAN pathogenesis. This pathway holds potential for further investigation to identify biomarkers and therapeutic targets in IgAN.

In autoreactive germinal centers (GC) initiated by a single rogue B cell clone, wild-type B cells expand and give rise to clones that target other autoantigens, known as epitope spreading. The chronic, progressive nature of epitope spreading calls for early interventions to limit autoimmune pathologies, but the kinetics and molecular requirements for wild-type B cell invasion and participation in GC remain largely unknown. With parabiosis and adoptive transfer approaches in a murine model of systemic lupus erythematosus, we demonstrate that wild-type B cells join existing GCs rapidly, clonally expand, persist, and contribute to autoantibody production and diversification. The invasion of autoreactive GCs by wild-type B cells required TLR7, B cell receptor specificity, antigen presentation, and type I interferon signaling. The adoptive transfer model provides a tool for identifying early events in the breaking of B cell tolerance in autoimmunity.

Background/Objectives: Obesity-associated metabolic dysfunction and inflammation can be ameliorated by bariatric surgery. While obesity is also linked to impaired B cell activation, differentiation, and persistence in response to infection and vaccination little is known about post-operative immune B cell compartment and to what extent dysregulation in B cell pathways can be reversed. To bridge this gap in knowledge, we carried out in-depth evaluation of B cell composition in individuals with obesity prior to and following bariatric surgery compared to lean controls. Subjects/Methods: We recruited individuals with obesity (BMI at least 35 kg/m²) before bariatric surgery (n = 21) and followed them up 6 months post-operatively (n = 17). As controls we recruited age- and sex-matched lean (BMI < 25) individuals (n = 18). We carried out comprehensive immunophenotyping of peripheral blood B cells as well as interrogated their association with inflammatory and metabolic parameters. Results: In obesity the balance of antigen-inexperienced and memory B cells in the peripheral blood is altered, with an expansion of naïve and a reduction in total memory B cells. 6 months following bariatric surgery this balance is restored. However, post-operative patients are uniquely characterised by an increase in B cell subsets associated with chronic inflammation – CD11c⁺CXCR5^-IgD^-CD27^- double negative 2 (DN2) B cells and CD27⁺CD38⁺⁺ plasmablasts. Correlations between B cells subsets, inflammatory and metabolic parameters were distinct in lean people and individuals with obesity pre- and post-bariatric surgery. Conclusions: Bariatric surgery patients display a unique B cell profile 6 months post-operatively; this bears minimal resemblance to that of pre-operative patients and only partially overlaps with that of lean controls. Post-operative differences in the B cell compartment compared to lean controls are detected despite global amelioration of inflammation and restoration of metabolic health. Collectively, this indicates that bariatric surgery creates a specific immunometabolic state with potential implications for health outcomes.

Background/Objectives. Obesity-associated metabolic dysfunction and inflammation can be ameliorated by bariatric surgery. While obesity is also linked to impaired B cell activation, differentiation, and persistence in response to infection and vaccination little is known about post-operative immune B cell compartment and to what extent dysregulation in B cell pathways can be reversed. To bridge this gap in knowledge, we carried out in-depth evaluation of B cell composition in obese individuals prior to and following bariatric surgery compared to lean controls. Subjects/Methods. We recruited individuals with obesity (BMI at least 35 kg/m²) before bariatric surgery (n = 21) and followed them up 6 months post-operatively (n = 17). As controls we recruited age- and sex-matched lean (BMI < 25) individuals (n = 18). We carried out comprehensive immunophenotyping of peripheral blood B cells as well as interrogated their association with inflammatory and metabolic parameters. Results. In obesity the balance of antigen-inexperienced and memory B cells in the peripheral blood is altered, with an expansion of naïve and a reduction in total memory B cells. 6 months following bariatric surgery this balance is restored. However, post-operative patients are uniquely characterised by an increase in B cell subsets associated with chronic inflammation – CD11c⁺CXCR5⁻IgD⁻CD27⁻ double negative 2 (DN2) B cells and CD27⁺CD38⁺⁺ plasmablasts. Correlations between B cells subsets, inflammatory and metabolic parameters were distinct in lean and obese individuals pre- and post-bariatric surgery. Conclusions. Bariatric surgery patients display a unique B cell profile 6 months post-operatively; this bears minimal resemblance to that of pre-operative patients and only partially overlaps with that of lean controls. Post-operative differences in the B cell compartment compared to lean controls are detected despite global amelioration of inflammation and restoration of metabolic health. Collectively, this indicates that bariatric surgery creates a specific immunometabolic state with potential implications for health outcomes.

Summary: Obesity increases the risk of type 2 diabetes mellitus, cardiovascular disease, fatty liver disease, and cancer. It is also linked with more severe complications from infections, including COVID-19, and poor vaccine responses. Chronic, low-grade inflammation and associated immune perturbations play an important role in determining morbidity in people living with obesity. The contribution of B cells to immune dysregulation and meta-inflammation associated with obesity has been documented by studies over the past decade. With a focus on human studies, here we consolidate the observations demonstrating that there is altered B cell subset composition, differentiation, and function both systemically and in the adipose tissue of individuals living with obesity. Finally, we discuss the potential factors that drive B cell dysfunction in obesity and propose a model by which altered B cell subset composition in obesity underlies dysfunctional B cell responses to novel pathogens.