Dysregulated germinal center reaction with expanded T follicular helper cells in autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy lymph nodes.

BACKGROUND: Autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED, also called APS-1) is an inborn error of immunity with clear signs of B-cell autoimmunity such as neutralizing anti-IFN antibodies. In APECED, mutations in the AIRE gene impair thymic negative selection of T cells. The resulting T-cell alterations may then cause dysregulation of B-cell responses. However, no analysis of interactions of T and B cells in the germinal centers (GCs) in patients' secondary lymphatic tissues has been reported. OBJECTIVE: This study examined the relationship between B cells and follicular T helper cells (TfH) in peripheral blood and lymph node (LN) GCs in patients with APECED. METHODS: Immunophenotyping of peripheral blood B cells and TfH was performed for 24 patients with APECED. Highly multiplexed fluorescent immunohistochemical staining was performed on 7 LN biopsy samples from the patients to study spatial interactions of lymphocytes in the GCs at the single-cell level. RESULTS: The patients' peripheral B-cell phenotype revealed skewing toward a mature B-cell phenotype with marked loss of transitional and naive B cells. The frequency of circulating TfH cells was diminished in the patients, while in the LNs the TfH population was expanded. In LNs the overall frequency of Treg cells and interactions of Treg cells with nonfollicular T cells were reduced, suggesting that aberrant Treg cell function might fail to restrain TfH differentiation. CONCLUSIONS: GC reactions are disrupted in APECED as a result of defective T-cell control.

Ectopic germinal centers in the thymus accurately predict prognosis of myasthenia gravis after thymectomy.

The ability of thymic histopathology to predict the long-term impact of thymectomy in non-thymomatous myasthenia gravis (NTMG) is mainly uncharted. We applied digital pathology to quantitatively characterize differences of thymic histology between early-onset (EOMG) and late-onset MG (LOMG) and to investigate the role of thymic changes for thymectomy outcomes in MG. We analyzed 83 thymic H&E slides from thymectomized NTMG patients, of which 69 had EOMG and 14 LOMG, using digital pathology open-access software QuPath. We compared the results to the retrospectively assessed clinical outcome at two years after thymectomy and at the last follow-up visit where complete stable remission and minimal use of medication were primary outcomes. The automated annotation pipeline was an effective and reliable way to analyze thymic H&E samples compared to manual annotation with mean intraclass correlation of 0.80. The ratio of thymic tissue to stroma and fat was increased in EOMG compared to LOMG (p = 8.7e-07), whereas no difference was observed in the ratio of medulla to cortex between these subtypes. AChRAb seropositivity correlated with the number of ectopic germinal centers (eGC; p = 0.00067) but not with other histological areas. Patients with an increased number of eGCs had better post-thymectomy outcomes at two years after thymectomy (p = 0.0035) and at the last follow-up (p = 0.0267). ROC analysis showed that eGC area predicts thymectomy outcome in EOMG with an AUC of 0.79. Digital pathology can thus help in providing a predictive tool to the clinician, the eGC number, to guide the post-thymectomy treatment decisions in EOMG patients.

A skewed ratio of free light chains is more common in patients with late-onset than early-onset myasthenia gravis.

Myasthenia gravis (MG) is an autoantibody-mediated neuromuscular disease with an unpredictable clinical course. Serum free light chains (FLCs) have risen as a promising biomarker for MG, but their role in different subtypes of MG and in predicting disease progression is still uncharted. We investigated plasma from 58 generalized MG patients during post-thymectomy follow-up to determine κ and λ FLC and κ/λ ratio. In a subcohort of 30 patients, we examined the expression of 92 proteins associated with immuno-oncology using Olink. We further studied the ability of FLCs or proteomic markers to differentiate disease severity. Patients with late-onset MG (LOMG) displayed significantly higher mean κ/λ ratio than patients with early-onset MG (P = 0.004). Inducible T-cell co-stimulator ligand (ICOSLG), matrix metalloproteinase 7 (MMP7), hepatocyte growth factor (HGF), and arginase 1 (ARG1) were differentially expressed in MG patients compared to healthy controls. There were no significant associations between clinical outcomes and FLCs or the assayed proteins. In conclusion, an elevated κ/λ ratio suggests long-lasting aberrant clonal plasma cell function in LOMG. Immuno-oncology-related proteomic analysis showed alterations in immunoregulatory pathways. Our findings pinpoint the FLC ratio as a biomarker for LOMG and call for further investigation of the immunoregulatory pathways in MG.

Loss-of-function mutation in IKZF2 leads to immunodeficiency with dysregulated germinal center reactions and reduction of MAIT cells.

The Ikaros family transcription factors regulate lymphocyte development. Loss-of-function variants in IKZF1 cause primary immunodeficiency, but Ikaros family members IKZF2 and IKZF3 have not yet been associated with immunodeficiency. Here, we describe a pedigree with a heterozygous truncating variant in IKZF2, encoding the transcriptional activator and repressor Helios, which is highly expressed in regulatory T cells and effector T cells, particularly of the CD8+ T cell lineage. Protein-protein interaction analysis revealed that the variant abolished heterodimerization of Helios with Ikaros and Aiolos and also prevented Helios binding to members of the Mi-2/NuRD chromatin remodeling complex. Patients carrying the IKZF2 variant presented with a combined immunodeficiency phenotype characterized by recurrent upper respiratory infections, thrush and mucosal ulcers, and chronic lymphadenopathy. With extensive immunophenotyping, functional assays, and transcriptional analysis, we show that reduced Helios expression was associated with chronic T cell activation and increased production of proinflammatory cytokines both in effector and regulatory T cells. Lymph node histology from patients indicated dysregulated germinal center reactions. Moreover, affected individuals displayed a profound reduction in circulating MAIT cell numbers. In summary, we show that this previously undescribed loss-of-function variant in Helios leads to an immunodeficiency with signs of immune overactivation.