A sex-biased imbalance between Tfr, Tph, and atypical B cells determines antibody responses in COVID-19 patients

Regulatory cytokines modulate early isotype-specific response associated with COVID-19 survival

Identifying immune markers driving early and effective antibody response in patients with severe coronavirus disease 2019 (COVID-19) is critical due to the threat of future coronavirus pandemics, incomplete global vaccination, and suboptimal booster coverage. Patients with life-threatening severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection are characterized by dysregulated thromboinflammation and cytokine storm that could influence the isotype virus-specific antibody response and the subsequent clinical outcome. We investigated the association between COVID-19-related mortality with the dynamics, magnitude, and relative avidity of nucleoprotein (N), spike (S), and receptor-binding domain (RBD)-specific IgM, IgA, and IgG in circulation. We also assessed the relationship between the virus-specific antibody responses and cytokine patterns, as well as systemic and pulmonary thromboinflammation markers. This multicenter study included COVID-19 patients hospitalized early in the pandemic, classified as survivors (n=62) and non-survivors (n=17). We developed indirect enzyme-linked immunosorbent assays (ELISAs) to evaluate each virus-specific isotype using well-characterized outpatient COVID-19 (n=180) and pre-pandemic cohorts (n=111). The pro-inflammatory interleukin (IL)-6 and tumor necrosis factor (TNF)-α, as well as the regulatory IL-10, transforming growth factor (TGF)-β1, and soluble tumor necrosis factor receptor I (sTNFRI) levels were evaluated. The ELISAs performed highly for all virus-specific isotypes, although modest for IgM-N. Non-survivors increased N-specific, but no S-specific, IgM and IgA responses throughout the disease course and, more notably, a delayed class switching to IgG-S and IgG-RBD compared to survivors. No differences were observed in the virus-specific IgG relative avidity. Survivors exhibited an antibody response proportional to the degree of systemic and pulmonary thromboinflammation, whereas non-survivors showed those dissociated because of their uncontrolled severe thromboinflammation. Only the survivors showed a dominant regulatory cytokine pattern in the early phase of infection (<10 days after symptoms onset), which strongly correlated with developing IgG-S and IgG-RBD protective antibodies. We developed easy-to-use immune assays that enable patient monitoring and identify at-risk populations in low- to middle-income regions. Non-survivors displayed an ineffective N-mediated antibody response, marked by an inability to control inflammation and a compromised time-dependent class switching toward S and RBD-specific IgG. The regulatory cytokine axis, including TGF-β1, maybe a critical immune correlate of effective antibody-mediated immunity in COVID-19.

Single cell suppression profiling of human regulatory T cells

Regulatory T cells (Treg) play an important role in regulating immune homeostasis in health and disease. Traditionally their suppressive function has been assayed by mixing purified cell populations, which does not provide an accurate picture of a physiologically relevant response. To overcome this limitation, we here develop 'single cell suppression profiling of human Tregs' (scSPOT). scSPOT uses a 52-marker CyTOF panel, a cell division detection algorithm, and a whole PBMC system to assess the effect of Tregs on all other cell types simultaneously. In this head-to-head comparison, we find Tregs having the clearest suppressive effects on effector memory CD8 T cells through partial division arrest, cell cycle inhibition, and effector molecule downregulation. Additionally, scSPOT identifies a Treg phenotypic split previously observed in viral infection and propose modes of action by the FDA-approved drugs Ipilimumab and Tazemetostat. scSPOT is thus scalable, robust, widely applicable, and may be used to better understand Treg immunobiology and screen for therapeutic compounds.

Occurrence and role of Tph cells in various renal diseases

A new population of peripheral helper T (Tph) cells has been identified and contributed to various autoimmune diseases. Tph cells can secrete interleukin-21 (IL-21), interferon (IFN) and C-X-C motif chemokine ligand 13 (CXCL13) to moderate renal disease. Moreover, Tph cells can congregate in huge numbers and immerse within inflamed tissue. Compared to Tfh cells, Tph cells express high programmed cell death protein 1 (PD-1), major histocompatibility complex II (MHC-II), C-C chemokine receptor 2 (CCR2) and C-C chemokine receptor 5 (CCR5) but often lack expression of the chemokine receptor C-X-C chemokine receptor 5 (CXCR5). They display features distinct from other T cells, which are uniquely poised to promote responses and antibody production of B cells within pathologically inflamed non-lymphoid tissues and a key feature of Tph cells. In this review, we summarize recent findings on the role of Tph cells in chronic kidney disease, acute kidney injury, kidney transplantation and various renal diseases.

Atypical and non-classical CD45RBlo memory B cells are the majority of circulating SARS-CoV-2 specific B cells following mRNA vaccination or COVID-19

Resting memory B cells can be divided into classical or atypical groups, but the heterogenous marker expression on activated memory B cells makes similar classification difficult. Here, by longitudinal analysis of mass cytometry and CITE-seq data from cohorts with COVID-19, bacterial sepsis, or BNT162b2 mRNA vaccine, we observe that resting B cell memory consist of classical CD45RB+ memory and CD45RBlo memory, of which the latter contains of two distinct groups of CD11c+ atypical and CD23+ non-classical memory cells. CD45RB levels remain stable in these cells after activation, thereby enabling the tracking of activated B cells and plasmablasts derived from either CD45RB+ or CD45RBlo memory B cells. Moreover, in both COVID-19 patients and mRNA vaccination, CD45RBlo B cells formed the majority of SARS-CoV2 specific memory B cells and correlated with serum antibodies, while CD45RB+ memory are activated by bacterial sepsis. Our results thus identify that stably expressed CD45RB levels can be exploited to trace resting memory B cells and their activated progeny, and suggest that atypical and non-classical CD45RBlo memory B cells contribute to SARS-CoV-2 infection and vaccination.

Chemokine receptors in COVID-19 infection

Chemokine receptors play diverse roles in the immune response against pathogens by recruiting innate and adaptive immune cells to sites of infection. However, their involvement could also be detrimental, causing tissue damage and exacerbating respiratory diseases by triggering histological alterations such as fibrosis and remodeling. This chapter reviews the role of chemokine receptors in the immune defense against SARS-CoV-2 infection. In COVID-19, CXCR3 is expressed mainly in T cells, and its upregulation is related to an increase in SARS-CoV-2-specific antibodies but also to COVID-19 severity. CCR5 is a key player in T-cell recruitment, and its suppression leads to reduced inflammation and viremia levels. Conversely, CXCR6 is implicated in the aberrant migration of memory T cells within airways. On the other hand, increased CCR4+ cells in the blood and decreased CCR4+ cells in lung cells are associated with severe COVID-19. Additionally, CCR2 is associated with an increase in macrophage recruitment to lung tissues. Elevated levels of CXCR1 and CXCR2, which are predominantly expressed in neutrophils, are associated with the severity of the disease, and finally, the expression of CX3CR1 in cytotoxic T lymphocytes affects the retention of these cells in lung tissues, thereby impacting the severity of COVID-19. Despite the efforts of many clinical trials to find effective therapies for COVID-19 using chemokine receptor inhibitors, no conclusive results have been found due to the small number of patients, redundancy, and co-expression of chemokine receptors by immune cells, which explains the difficulty in finding a single therapeutic target or effective treatment.

Peripheral helper T cells in human diseases

Peripheral helper T cells (Tph) are a specialized subset of CD4+ T cells with the ability to help B cells and induce antibody production. Although usually located in ectopic lymphoid-like structures (ELS), inside the peripheral blood, Tph cells can also be identified. The aberrant proliferation and functions of Tph cells are commonly found in the patients with disease. In this review, first we will summarize the biological characteristics of Tph cells, such as the expression of surface molecules, transcription factors and cytokines, and discuss its B cell help functions. Tph cells also have roles in a wide range of human diseases, including autoimmune diseases, infectious diseases, malignancies etc. Therefore, there is a strong interest in targeting Tph cells to improve treat strategies of human diseases.

Sarcoidosis-related autoimmune inflammation in COVID-19 convalescent patients

Currently, there are a large number of reports about the development of autoimmune conditions after COVID-19. Also, there have been cases of sarcoid-like granulomas in convalescents as a part of the post-COVID-19 syndrome. Since one of the etiological theories of sarcoidosis considers it to be an autoimmune disease, we decided to study changes in the adaptive humoral immune response in sarcoidosis and SARS-CoV-2 infection and to find out whether COVID-19 can provoke the development of sarcoidosis. This review discusses histological changes in lymphoid organs in sarcoidosis and COVID-19, changes in B cell subpopulations, T-follicular helper cells (Tfh), and T-follicular regulatory cells (Tfr), and analyzes various autoantibodies detected in these pathologies. Based on the data studied, we concluded that SARS-CoV-2 infection may cause the development of autoimmune pathologies, in particular contributing to the onset of sarcoidosis in convalescents.

Increased blood immune regulatory cells in severe COVID-19 with autoantibodies to type I interferons

The hallmark of severe COVID-19 is an uncontrolled inflammatory response, resulting from poorly understood immunological dysfunction. While regulatory T (Treg) and B (Breg) cells, as the main elements of immune homeostasis, contribute to the control of hyperinflammation during COVID-19 infection, we hypothesized change in their levels in relation to disease severity and the presence of autoantibodies (auto-Abs) to type I IFNs. Cytometric analysis of blood of 62 COVID-19 patients with different severities revealed an increased proportion of conventional (cTreg; CD25+FoxP3+) and unconventional (uTreg; CD25-FoxP3+) Tregs, as well as the LAG3+ immune suppressive form of cTreg/uTreg, in the blood of severe COVID-19 cases compared to the milder, non-hospitalized cases. The increase in blood levels of cTreg/uTreg, but not LAG3+ cTreg/uTreg subtypes, was even higher among patients with severe COVID-19 and auto-Abs to type I IFNs. Regarding Bregs, compared to the milder, non-hospitalized cases, the proportion of IL-35+ and IL-10+ Bregs was elevated in the blood of severe COVID-19 patients, and to a higher extent in those with auto-Abs to type I IFNs. Moreover, blood levels of cTreg, LAG3+ cTreg/uTreg, and IL-35+ and IL-10+ Breg subtypes were associated with lower blood levels of proinflammatory cytokines such as IL-6, IL-17, TNFα, and IL-1β. Interestingly, patients who were treated with either tocilizumab and/or a high dose of Vitamin D had higher blood levels of these regulatory cells and better control of the proinflammatory cytokines. These observations suggest that perturbations in the levels of immunomodulatory Tregs and Bregs occur in COVID-19, especially in the presence of auto-Abs to type I IFNs.

COVID-19 patients display changes in lymphocyte subsets with a higher frequency of dysfunctional CD8lo T cells associated with disease severity

This work examines cellular immunity against SARS-CoV-2 in patients from Córdoba, Argentina, during two major waves characterized by different circulating viral variants and different social behavior. Using flow cytometry, we evaluated the main lymphocyte populations of peripheral blood from hospitalized patients with moderate and severe COVID-19 disease. Our results show disturbances in the cellular immune compartment, as previously reported in different cohorts worldwide. We observed an increased frequency of B cells and a significant decrease in the frequency of CD3+ T cells in COVID-19 patients compared to healthy donors (HD). We also found a reduction in Tregs, which was more pronounced in severe patients. During the first wave, the frequency of GZMB, CD107a, CD39, and PD-1-expressing conventional CD4+ T (T conv) cells was significantly higher in moderate and severe patients than in HD. During the second wave, only the GZMB+ T conv cells of moderate and severe patients increased significantly. In addition, these patients showed a decreased frequency in IL-2-producing T conv cells. Interestingly, we identified two subsets of circulating CD8+ T cells with low and high CD8 surface expression in both HD and COVID-19 patients. While the percentages of CD8hi and CD8lo T cells within the CD8+ population in HD are similar, a significant increase was observed in CD8lo T cell frequency in COVID-19 patients. CD8lo T cell populations from HD as well as from SARS-CoV-2 infected patients exhibited lower frequencies of the effector cytokine-producing cells, TNF, IL-2, and IFN-γ, than CD8hi T cells. Interestingly, the frequency of CD8lo T cells increased with disease severity, suggesting that this parameter could be a potential marker for disease progression. Indeed, the CD8hi/CD8lo index helped to significantly improve the patient's clinical stratification and disease outcome prediction. Our data support the addition of, at least, a CD8hi/CD8lo index into the panel of biomarkers commonly used in clinical labs, since its determination may be a useful tool with impact on the therapeutic management of the patients.

Tuberculosis and COVID-19 Dually Affect Human Th17 Cell Immune Response

COVID-19 infection not only profoundly impacts the detection of tuberculosis infection (Tbc) but also affects modality in tuberculosis patient immune response. It is important to determine immune response alterations in latent tuberculosis infection as well as in SARS-CoV-2-infected tuberculosis patients. Such changes may have underlying effects on the development and course of further tuberculosis. Here, we aimed to review the characteristics of immune response in TB patients or convalescent COVID-19 patients with latent TB infection (LTBI).

MATERIALS AND METHODS

We analyzed the features of immune response in tuberculosis and COVID-19 patients. For this, we analyzed publications released from December 2019 to March 2023; those which were published in accessible international databases ("Medline", "PubMed", "Scopus") and with keywords such as "COVID-19", "SARS-CoV-2", "tuberculosis", "pulmonary tuberculosis", "latent tuberculosis infection", "Treg", "follicular Treg", and "Treg subsets", we considered.

RESULTS

Through our analysis, we found that tuberculosis patients who had been infected with COVID-19 previously and elevated Th1 and Th2 cell levels. High levels of Th1 and Th2 cells may serve as a positive marker, characterizing activated immune response during TB infection. COVID-19 or post-COVID-19 subjects showed decreased Th17 levels, indicating a lack of tuberculosis development. Moreover, the typical course of tuberculosis is associated with an increase in Treg level, but COVID-19 contributes to a hyperinflammatory response.

CONCLUSION

According to the data obtained, the course of tuberculosis proceeds in a dissimilar way due to the distinct immune response, elicited by SARS-CoV-2. Importantly, the development of active tuberculosis with a severe course is associated with a decline in Treg levels. Both pathogens lead to disturbed immune responses, increasing the risk of developing severe TB. The insights and findings of this paper may be used to improve the future management of individuals with latent and active tuberculosis.