Disordered Balance of T-Cell Subsets in Arterial Tertiary Lymphoid Organs in Immunoglobulin G4-Related Vascular Disease

Unraveling Novel Subsets of Lymphocytes Involved in Sac Expansion in the Tertiary Lymphoid Structure Within an Abdominal Aortic Aneurysm

BACKGROUND

Chronic inflammation is involved in the development of abdominal aortic aneurysm (AAA). A tertiary lymphoid structure (TLS) within vascular lesions has recently been focused on for its role in modulation of inflammation in local tissues. We aimed to elucidate the relationships between TLS and pathophysiology of AAA.

METHODS

Abdominal aortic samples obtained from 37 patients with AAA (men/women: 34/3, age: 72.8±9.9 years) and 15 autopsied patients who died from non-aortic events (men/women: 11/4, age: 65.5±9.8 years) were investigated.

RESULTS

TLSs in AAA lesions were confirmed by focal infiltration of CD3-positive cells surrounding germinal center-like structures containing CD20-positive cells between the tunica adventitia and tunica media layers. The formation of a TLS was significantly more prevalent in AAA patients than in autopsied patients. The number of TLSs in AAA lesions was positively correlated with sac diameter (r=0.357, P=0.035) and the amount of intraluminal thrombosis (r=0.466, P=0.005). T cells and B cells were predominant cellular populations among CD45+ cells in AAA lesions. There was a significantly positive correlation between the proportions of interfollicular T follicular helper (CD3+CD4+CD45RA-CXCR5+PD-1+) cells and double negative B (CD3-CD19+IgD-CD27-) cells, and they were positively correlated with sac diameter, intraluminal thrombosis, and serum lipids. Deposited single-cell RNA-sequencing data for AAA showed that T follicular helper cells and double negative B cells were associated with lipid metabolism, T cell activation/proliferation and inflammation.

CONCLUSIONS

The formation of a TLS in AAA lesions is associated with sac diameter and intraluminal thrombosis in connection with interfollicular T follicular helper cells and double negative B cells, which may contribute to the pathophysiology of AAA and might be novel therapeutic targets for the development of AAA.

Single-cell transcriptome analysis reveals cellular heterogeneity in the aortas of Takayasu arteritis

OBJECTIVES

Takayasu arteritis (TAK) is an inflammatory vasculitis that affects the aorta and its primary branches. The pathogenesis of TAK remains elusive, yet identifying key cell types in the aorta of TAK patients is crucial for uncovering cellular heterogeneity and discovering potential therapeutic targets.

METHODS

This study utilized single-cell transcriptome analysis on aortic specimens from three TAK patients, with control data sourced from a publicly available database (GSE155468). Additionally, bulk RNA sequencing was performed on peripheral CD4 + and CD8 + T cells from eight TAK patients and eight matched healthy volunteers. All participants were recruited at Anzhen Hospital, Capital Medical University, China, between January 2020 and December 2023.

RESULTS

Single-cell transcriptome analysis identified 11 predominant cell types in aortic tissues, with notable differences in proportions between TAK patients and controls. T cells, B cells, macrophages, smooth muscle cells (SMCs), and fibroblasts exhibited subtype-specific gene expression signatures, with notable changes in interactions between T cells, B cells, and monocyte-macrophages, highlighting their active involvement in the pathogenesis of TAK. Bulk RNA-Seq analysis of peripheral blood T cells from TAK patients showed an upregulation of complement system genes, underscoring the significance of the complement signaling pathway in TAK's immunopathogenesis.

CONCLUSION

The findings underscore the active involvement of various immune and structural cells in the aortic tissues of TAK patients and reveal the presence of the complement signaling pathway in peripheral blood T cells. These insights are instrumental for identifying novel therapeutic targets and developing robust disease monitoring methods for TAK.

The immunological pathogenesis of IgG4-related disease categorized by clinical characteristics

IgG4-related disease (IgG4-RD) is an immune disorder characterized by organ enlargement and fibrosis leading to functional impairment. Key immune cell subsets contributing to the pathogenesis of IgG4-RD include T follicular helper 2 cells (Tfh2), Tfh1, CX3CR1 + cytotoxic T cells (CX3CR1 + CTLs), Tregs and IgG4 + B cells. Tfh2 and Tregs are commonly involved in inducing IgG4 class-switching in this disease. Importantly, IgG4-RD can be classified into four clinical phenotypes based on the distribution of affected organs, with each phenotype showing different dominant immune cell subsets involved in its pathogenesis. Specifically, the clinical phenotype of retroperitoneal fibrosis/aortitis is characterized by CX3CR1 + CTLs as the dominant key immune cell subset, while Mikulicz disease with systemic involvement is dominated by Tfh2. In addition to classification based on organ distribution, IgG4-RD can also be categorized into phenotypes associated with malignancy or allergy. The malignancy phenotype is characterized by an increase in CXCR5 + CD2-double negative T cells compared to the allergy phenotype, along with a decrease in naive CD8 + T cells. Moreover, several autoantigens have been identified, and the presence of autoimmune phenotype has been revealed. Due to the pathogenicity of IgG1-type autoantibodies, Tfh1 may be important inducing IgG1 class-switching by IFNγ in autoimmune phenotype. In IgG4-RD with hypocomplementemia, activation of the complement pathway is thought to be induced by IgG1 or IgG2 antibodies, suggesting the involvement of Tfh1 in the disease pathogenesis. Therefore, elucidating the immunological features specific to each clinical characteristic is believed to lead to a deeper understanding of the pathogenesis of IgG4-RD and the discovery of novel therapeutic targets. This review provides an overview of the immunological mechanisms common to IgG4-RD as well as those specific to each clinical characteristic.

Clinicopathological analysis of enlarged abdominal aortic aneurysms after endovascular aneurysm repair and the relationship with occult IgG4-related vascular disease

PURPOSE

To evaluate the incidence of IgG4-related vascular disease (IgG4-VD) in aneurysm enlargement after endovascular aneurysm repair (EVAR).

METHODS

Of 1482 EVAR cases in which patients underwent initial treatment at our hospital, 33 patients who underwent open surgery for an enlarged aneurysm were retrospectively identified. Histopathological examination of the aneurysm wall specimens was performed and the relationship of the histopathological findings with IgG4-VD was investigated.

RESULTS

The median aneurysm diameter at EVAR was 53 mm (interquartile range [IQR] 50-55), and the aneurysm diameter at open surgery was 79 mm (IQR 75-88). Six patients (18%) were histopathologically diagnosed with IgG4-VD. Relative to the non-IgG4-VD cases, the patients with IgG4-VD had a higher incidence of coronary artery disease (83% vs. 30%, p = 0.015) and greater aneurysm wall thickness at the time of open surgery (2.4 mm vs. 1.6 mm, p < 0.001). Serum IgG4 levels were significantly higher in patients with IgG4-VD than in those without IgG4-VD (218 mg/L vs. 46 mg/L, p = 0.002).

CONCLUSIONS

IgG4-VD was found in 18% cases with enlarged aneurysms after EVAR. If aneurysm enlargement is observed after EVAR, measurement of the aneurysm wall thickness using preoperative CT angiography and the evaluation of serum IgG4 levels could be useful for diagnosing occult IgG4-VD.

Validation of the Diagnostic Criteria for IgG4-Related Periaortitis/Periarteritis and Retroperitoneal Fibrosis (IgG4PA/RPF) 2018, and Proposal of a Revised 2023 Version for IgG4-Related Cardiovascular/Retroperitoneal Disease

BACKGROUND

In 2018, diagnostic criteria were introduced for IgG4-related periaortitis/periarteritis and retroperitoneal fibrosis (PA/RPF). This study assessed the existing criteria and formulated an improved version.

METHODS AND RESULTS

Between August 2022 and January 2023, we retrospectively analyzed 110 Japanese patients diagnosed with IgG4-related disease (IgG4-RD) involving cardiovascular and/or retroperitoneal manifestations, along with 73 non-IgG4-RD patients ("mimickers") identified by experts. Patients were stratified into derivation (n=88) and validation (n=95) groups. Classification as IgG4-RD or non-IgG4-RD was based on the 2018 diagnostic criteria and various revised versions. Sensitivity and specificity were calculated using experts' diagnosis as the gold standard for the diagnosis of true IgG4-RD and mimickers. In the derivation group, the 2018 criteria showed 58.5% sensitivity and 100% specificity. The revised version, incorporating "radiologic findings of pericarditis", "eosinophilic infiltration or lymphoid follicles", and "probable diagnosis of extra-PA/-RPF lesions", improved sensitivity to 69.8% while maintaining 100% specificity. In the validation group, the original and revised criteria had sensitivities of 68.4% and 77.2%, respectively, and specificities of 97.4% and 94.7%, respectively.

CONCLUSIONS

Proposed 2023 revised IgG4-related cardiovascular/retroperitoneal disease criteria show significantly enhanced sensitivity while preserving high specificity, achieved through the inclusion of new items in radiologic, pathological, and extra-cardiovascular/retroperitoneal organ categories.

Clinicopathological features of immunoglobulin G4-related constrictive pericarditis

AIM

Constrictive pericarditis (CP) is characterised by scarring fibrosis and a loss of pericardial elasticity, which causes heart failure. IgG4 (immunoglobulin G4)-related disease (IgG4-RD) is a systemic fibro-inflammatory disease characterised by the infiltration of IgG4-immunopositive plasmacytes and high serum IgG4 levels that frequently shape tumorous lesions. Although pericardial involvement of IgG4-RD is rare, with indications of CP, pericardial effusion and irregular masses, the clinical and pathological features remain unclear. In this study, we examined the relationship between CP and IgG4-RD.

METHODS

Among 35 thick-walled CP cases (histologically pericardial thickening ≥2 mm), eight cases were aetiology identified. Using the diagnostic criteria for IgG4-RD, 11 cases were classified as IgG4-CP, whereas the remainder were considered true idiopathic CP (16 cases) and the clinical pathological features were evaluated.

RESULTS

Compared with the other groups, the IgG4-CP group was more common in men and associated with low-grade fever and massive pericardial effusion with frequent recurrence. Deaths resulting from heart failure occurred in a few cases of the IgG4-CP group, but not in other groups. An increase in C-reactive protein and a high positivity rate of anti-nuclear antibodies frequently occurred in the IgG4-CP group. Histologically, the IgG4-CP group included lymphoid follicle, eosinophil infiltration and few calcifications.

CONCLUSIONS

Pericardial IgG4-RD occurs not only as nodular lesions, but also as thick-walled CP, and accounts for approximately 40% of thick-walled CP cases of unknown cause. The predominant clinical characteristic was refractory and recurrent pericardial effusion. Recognising IgG4-RD as a cause of CP is important to initiate appropriate therapy.

T-Cell/B-Cell Interactions in Atherosclerosis

Atherosclerosis is a complex inflammatory disease in which the adaptive immune response plays an important role. While the overall impact of T and B cells in atherosclerosis is relatively well established, we are only beginning to understand how bidirectional T-cell/B-cell interactions can exert prominent atheroprotective and proatherogenic functions. In this review, we will focus on these T-cell/B-cell interactions and how we could use them to therapeutically target the adaptive immune response in atherosclerosis.