The blind spot : inflammatory pathways and specific antigens in clinical phenotypes of pulmonary sarcoidosis

Sarcoidosis is a granulomatous multisystem disorder of unknown aetiology, primarily manifesting in the lungs. The disease appears in two forms, which are mainly distinguished based on clinical criteria; Löfgren's syndrome (LS) presents with acute onset, usually fever, active inflammation and characteristic symptoms such as bilateral hilar lymphadenopathy (BHL), erythema nodosum and/or ankle arthritis, but is also associated with spontaneous resolution and a good prognosis. In contrast, "non-LS" comprises a more heterogeneous patient group, with common characteristics being an insidious onset, slower disease progression and a higher risk of developing chronic disease, extrapulmonary manifestations and eventually pulmonary fibrosis. Despite advances in genetics, epidemiology, immunology and therapeutics during the past decades, the disease-triggering antigen(s) and the immunological mechanisms underlying different clinical phenotypes remain a "blind spot" - something that is known to exist but that the eye is, as yet, unable to perceive. Previous studies have shown the human leukocyte antigen (HLA)-DR allele HLA-DRB1*03 to associate closely with LS and a favourable clinical outcome. In these patients, local expansion of CD4+ T cells carrying the specific T cell receptor (TCR) variable (V) segment Vα2.3 in the lungs suggests specific antigen recognition, making these cells ideal tools in the quest for disease-triggering factors in sarcoidosis. The aims of this thesis were therefore to investigate on one hand the phenotype, functionality and ultimately antigen-specificity of TCR-specific CD4+ T cells, and on the other to improve understanding of immunological mechanisms underlying distinct clinical phenotypes of sarcoidosis. In HLA-DRB1*03+ patients with sarcoidosis, Vα2.3 was found to preferentially pair with the Vβ22 TCR segment on CD4+ T cells in the lung. Expression of activation markers on these cells indicated an advanced state of differentiation, consistent with prolonged antigen exposure, and a high degree of clonality, marked by appearance of identical and near-identical TCR α and β CDR3 sequences between patients. In addition, molecular modelling of the TCR Vα2.3/Vβ22-HLA-DRB1*03 complex revealed an ideal fit into the peptide-binding cleft of a peptide derived from the carboxyl (C)-terminal of cytoskeletal protein vimentin, implicating vimentin as a potential (auto)antigen in sarcoidosis and suggesting especially LS to harbour traits of autoimmunity. Accordingly, anti-vimentin IgG and IgA antibodies were detected in the lungs of sarcoidosis patients to a higher degree than in healthy individuals, and correlated with expression of the Vα2.3/Vβ22 TCR. HLA-DRB1*03+ patients also demonstrated lower total Ig counts, but stronger reactivity towards the vimentin C-terminal, ultimately suggesting a more antigen-driven, but less aggressive, cooperative T-B cell response in HLADRB1* 03-mediated disease. Particularly in LS patients, CD4+ T cells in the lung demonstrated simultaneous expression of T helper (TH) 1 transcriptional regulator T-bet and TH17 counterpart RORγT, which intriguingly correlated with non-chronic disease, and responded to stimuli with a broad array of cytokines, including interleukin (IL)-10, IL-2, IL-17A and IL-22, in addition to interferon (IFN)-γ, the main cytokine produced in non-LS patients. Moreover, expression of inhibitory receptors CTLA-4 and PD-1 indicated a higher degree of regulatory capacity compared to non-LS CD4+ T cells, where elevated expression of HLA-DR, CD127 and CD39 pointed towards a more pronounced effector profile. The discovery of marked CD8+ T cell proliferation in both patient groups provides further evidence for a hitherto unappreciated role of CD4+ T cells in restriction of cytotoxic T cell activity to prevent tissue damage in sarcoidosis, with loss of CTLA-4- and PD-1-mediated inhibition in non-LS patients exacerbating the risk of developing chronic disease and permanent scarring. Combined with reduced expression of adhesion marker CD44 in LS, this detailed characterisation outlines a possible mechanism for spontaneous resolution of granulomas. The collected findings of this thesis suggest fundamental differences in CD4+ T cell biology that may be of key importance for disease resolution and progression, respectively, in clinical phenotypes of pulmonary sarcoidosis. Moreover, the results presented constitute an important step forward in the search for diseasespecific antigens, and provide incentive for further exploration of sarcoidosis, and LS in particular, as an autoimmune condition, at least partly driven by cognate T and B cell reactivity to vimentin. Hopefully, these discoveries may shed further light upon the still-elusive enigma of sarcoidosis, act as a foundation for continued investigation of disease-instigating factors, and ultimately contribute to reconsideration of current disease classification

Mass Cytometry Identifies Distinct Lung CD4+ T Cell Patterns in Löfgren’s Syndrome and Non-Löfgren’s Syndrome Sarcoidosis

Sarcoidosis is a granulomatous disorder of unknown etiology, characterized by accumulation of activated CD4+ T cells in the lungs. Disease phenotypes Löfgren’s syndrome (LS) and “non-LS” differ in terms of clinical manifestations, genetic background, HLA association, and prognosis, but the underlying inflammatory mechanisms largely remain unknown. Bronchoalveolar lavage fluid cells from four HLA-DRB1*03+ LS and four HLA-DRB1*03− non-LS patients were analyzed by mass cytometry, using a panel of 33 unique markers. Differentially regulated CD4+ T cell populations were identified using the Citrus algorithm, and t-stochastic neighborhood embedding was applied for dimensionality reduction and single-cell data visualization. We identified 19 individual CD4+ T cell clusters differing significantly in abundance between LS and non-LS patients. Seven clusters more frequent in LS patients were characterized by significantly higher expression of regulatory receptors CTLA-4, PD-1, and ICOS, along with low expression of adhesion marker CD44. In contrast, 12 clusters primarily found in non-LS displayed elevated expression of activation and effector markers HLA-DR, CD127, CD39, as well as CD44. Hierarchical clustering further indicated functional heterogeneity and diverse origins of T cell receptor Vα2.3/Vβ22-restricted cells in LS. Finally, a near-complete overlap of CD8 and Ki-67 expression suggested larger influence of CD8+ T cell activity on sarcoid inflammation than previously appreciated. In this study, we provide detailed characterization of pulmonary T cells and immunological parameters that define separate disease pathways in LS and non-LS. With direct association to clinical parameters, such as granuloma persistence, resolution, or chronic inflammation, these results provide a valuable foundation for further exploration and potential clinical application

In Situ Humoral Immunity to Vimentin in HLA-DRB1*03+ Patients With Pulmonary Sarcoidosis

Vimentin has been implicated in pulmonary sarcoidosis as a T-cell autoantigen, particularly in the context of HLA-DRB1*03, the Vα2.3/Vβ22 T-cell receptor (TCR), and Löfgren’s syndrome. As vimentin is a known antigenic target in B-cell-mediated autoimmunity, we investigated in situ humoral anti-vimentin responses in pulmonary sarcoidosis and their relationship with HLA-DRB1*03. Sarcoid and healthy control (HC) lung biopsies were analyzed by multi-color confocal microscopy for B-cells, T-cells, proliferation, and vimentin, and compared to tonsillectomy tissue. Bronchoalveolar lavage fluid (BALF) and serum from 48 sarcoidosis patients and 15 healthy volunteers were typed for HLA-DRB1*03 and titrated for antibodies to full-length vimentin, vimentin truncations, and total IgG and IgA by ELISA. Presence of extracellular vimentin in BALF was determined by mass spectrometry and T-cell populations measured by flow cytometry. Sarcoid lung samples, especially from HLA-DRB1*03+ patients, contained vimentin-rich tertiary lymphoid structures and corresponding BALF was highly enriched for both IgG and IgA anti-vimentin antibody (AVA) titers. Furthermore, sarcoidosis patient BALF AVA concentrations (expressed as arbitrary units per milligram of total immunoglobulin isotype) correlated with the percentage of CD4+ T-cells expressing the Vα2.3/Vβ22 TCR. BALF antibody reactivity to the vimentin N-terminus was most prominent in HCs, whereas reactivity to the C-terminus (VimC-term) was enriched in the sarcoid lung. Specifically, HLA-DRB1*03+ patient BALF contained higher concentrations of anti-VimC-term antibodies than BALF from both HCs and HLA-DRB1*03− patients. Consistent with the lung as a site of AVA production, the concentration of AVAs in BALF was dramatically higher than in matched serum samples. Overall, there was a poor correlation between BALF and serum AVA concentrations. Together, these studies reveal the presence of linked in situ recognition of vimentin by both T- and B-cells in HLA-DRB1*03+ sarcoidosis patients, associated with a selective humoral immune response to the vimentin C-terminus

presentation_1_In Situ Humoral Immunity to Vimentin in HLA-DRB1*03+ Patients With Pulmonary Sarcoidosis.PDF

<p>Vimentin has been implicated in pulmonary sarcoidosis as a T-cell autoantigen, particularly in the context of HLA-DRB1*03, the Vα2.3/Vβ22 T-cell receptor (TCR), and Löfgren’s syndrome. As vimentin is a known antigenic target in B-cell-mediated autoimmunity, we investigated in situ humoral anti-vimentin responses in pulmonary sarcoidosis and their relationship with HLA-DRB1*03. Sarcoid and healthy control (HC) lung biopsies were analyzed by multi-color confocal microscopy for B-cells, T-cells, proliferation, and vimentin, and compared to tonsillectomy tissue. Bronchoalveolar lavage fluid (BALF) and serum from 48 sarcoidosis patients and 15 healthy volunteers were typed for HLA-DRB1*03 and titrated for antibodies to full-length vimentin, vimentin truncations, and total IgG and IgA by ELISA. Presence of extracellular vimentin in BALF was determined by mass spectrometry and T-cell populations measured by flow cytometry. Sarcoid lung samples, especially from HLA-DRB1*03⁺ patients, contained vimentin-rich tertiary lymphoid structures and corresponding BALF was highly enriched for both IgG and IgA anti-vimentin antibody (AVA) titers. Furthermore, sarcoidosis patient BALF AVA concentrations (expressed as arbitrary units per milligram of total immunoglobulin isotype) correlated with the percentage of CD4⁺ T-cells expressing the Vα2.3/Vβ22 TCR. BALF antibody reactivity to the vimentin N-terminus was most prominent in HCs, whereas reactivity to the C-terminus (Vim_C-term) was enriched in the sarcoid lung. Specifically, HLA-DRB1*03⁺ patient BALF contained higher concentrations of anti-Vim_C-term antibodies than BALF from both HCs and HLA-DRB1*03⁻ patients. Consistent with the lung as a site of AVA production, the concentration of AVAs in BALF was dramatically higher than in matched serum samples. Overall, there was a poor correlation between BALF and serum AVA concentrations. Together, these studies reveal the presence of linked in situ recognition of vimentin by both T- and B-cells in HLA-DRB1*03⁺ sarcoidosis patients, associated with a selective humoral immune response to the vimentin C-terminus.</p

Fatty acid 16:1ω5 as a proxy for arbuscular mycorrhizal fungal biomass : current challenges and ways forward

Fatty acid biomarkers have emerged as a useful tool to quantify biomass of various microbial groups. Here we focus on the frequent use of the fatty acid 16:1ω5 as a biomarker for arbuscular mycorrhizal (AM) fungi in soils. We highlight some issues with current applications of this method and use several examples from the literature to show that the phospholipid fatty acid (PLFA) 16:1ω5 can occur in high concentrations in soils where actively growing AM fungi are absent. Unless the study includes a control where the contribution of other microbes can be estimated, we advocate for the use of the neutral lipid fatty acid (NLFA) 16:1ω5. This biomarker has higher specificity, is more responsive to shifts in AM fungal biomass, and quantification can be conducted along with PLFA analysis without doubling analytical efforts. We conclude by contrasting various methods used to measure AM fungal biomass in soil and highlight future research needs to optimize fatty acid analyses