Where do T cell subsets stand in SARS-CoV-2 infection: An update

An outbreak of coronavirus disease 2019 (COVID-19) emerged in China in December 2019 and spread so rapidly all around the globe. It\u27s continued and spreading more dangerously in India and Brazil with higher mortality rate. Understanding of the pathophysiology of COVID-19 depends on unraveling of interactional mechanism of SARS-CoV-2 and human immune response. The immune response is a complex process, which can be better understood by understanding the immunological response and pathological mechanisms of COVID-19, which will provide new treatments, increase treatment efficacy, and decrease mortality associated with the disease. In this review we present a amalgamate viewpoint based on the current available knowledge on COVID-19 which includes entry of the virus and multiplication of virus, its pathological effects on the cellular level, immunological reaction, systemic and organ presentation. T cells play a crucial role in controlling and clearing viral infections. Several studies have now shown that the severity of the COVID-19 disease is inversely correlated with the magnitude of the T cell response. Understanding SARS-CoV-2 T cell responses is of high interest because T cells are attractive vaccine targets and could help reduce COVID-19 severity. Even though there is a significant amount of literature regarding SARS-CoV-2, there are still very few studies focused on understanding the T cell response to this novel virus. Nevertheless, a majority of these studies focused on peripheral blood CD4+ and CD8+ T cells that were specific for viruses. The focus of this review is on different subtypes of T cell responses in COVID-19 patients, Th17, follicular helper T (TFH), regulatory T (Treg) cells, and less classical, invariant T cell populations, such as δγ T cells and mucosal-associated invariant T (MAIT) cells etc that could influence disease outcome

Interleukin-10 Producing Regulatory B Cells Transformed CD4+CD25− Into Tregs and Enhanced Regulatory T Cells Function in Human Leprosy

Regulatory B cells (Bregs) are known to exhibit their regulatory functions through interleukin-10 (IL-10) cytokine which suppress inflammation. There are only a few studies explaining the phenotype and functioning of these cells in contribution to host immunity in leprosy. Here, we evaluated the role of IL-10 producing Bregs in the pathogenesis of leprosy and assessed their immunoregulatory effects on Tregs and effector T cells. We found an increased frequency of Bregs and increased expression of their immune modulatory molecules (IL-10, FoxP3, and PDL-1) in leprosy patients. The potential immunoregulatory mechanism of Bregs was also investigated using MACS sorted Teff (CD4+CD25−) and Treg (CD4+CD25+) cells were cocultured with Bregs to elucidate the effects of Bregs on effector T and regulatory T cells. Cell coculture results showed that purified Bregs cells from leprosy patients convert CD4+CD25− cells into CD4+CD25+ cells. Cell coculture experiments also demonstrated that leprosy derived IL-10 producing Bregs enhance FoxP3 and PD-1 expression in Tregs and enhanced Tregs activity. Blocking of IL-10 receptor confirmed that IL-10 producing Breg has immunomodulatory effect on Tregs and effector T cells as effector T cells are not converted into Tregs and enhanced expression of FoxP3 and PD-1 was not observed on Tregs. Collectively, these findings demonstrate that IL-10 producing Breg cells play an important mechanism in controlling the immunopathogenesis of leprosy and have an immunomodulatory effect on Tregs and effector T cells. Our findings may pave way for novel targets of IL-10 producing Bregs for immunotherapy in leprosy patients

Leprosy Reactions Show Increased Th17 Cell Activity and Reduced FOXP3+ Tregs with Concomitant Decrease in TGF-β and Increase in IL-6.

BACKGROUND:50% of leprosy patients suffer from episodes of Type 1/ reversal reactions (RR) and Type 2/ Erythema Nodosum Leprosum (ENL) reactions which lead to morbidity and nerve damage. CD4+ subsets of Th17 cells and CD25+FOXP3+ regulatory T cells (Tregs) have been shown to play a major role in disease associated immunopathology and in stable leprosy as reported by us and others. The aim of our study was to analyze their role in leprosy reactions. METHODOLOGY AND PRINCIPLE FINDINGS:Quantitative reverse transcribed PCR (qPCR), flowcytometry and ELISA were used to respectively investigate gene expression, cell phenotypes and supernatant levels of cytokines in antigen stimulated PBMC cultures in patients with stable disease and those undergoing leprosy reactions. Both types of reactions are associated with significant increase of Th17 cells and associated cytokines IL-17A, IL-17F, IL-21, IL-23 and chemokines CCL20, CCL22 as compared to matching stable forms of leprosy. Concurrently patients in reactions show reduction in FOXP3+ Treg cells as well as reduction in TGF-β and increase in IL-6. Moreover, expression of many T cell markers, cytokines, chemokines and signaling factors were observed to be increased in RR as compared to ENL reaction patients. CONCLUSIONS:Patients with leprosy reactions show an imbalance in Th17 and Treg populations. The reduction in Treg suppressor activity is associated withhigherTh17cell activity. The combined effect of reduced TGF-β and enhanced IL-6, IL-21 cytokines influence the balance between Th17 or Treg cells in leprosy reactions as reported in the murine models and autoimmune diseases. The increase in Th17 cell associated cytokines may contribute to lesional inflammation

Increase in TGF-β Secreting CD4⁺CD25⁺ FOXP3⁺ T Regulatory Cells in Anergic Lepromatous Leprosy Patients

<div><p>Background</p><p>Lepromatous leprosy caused by <i>Mycobacterium leprae</i> is associated with antigen specific T cell unresponsiveness/anergy whose underlying mechanisms are not fully defined. We investigated the role of CD25⁺FOXP3⁺ regulatory T cells in both skin lesions and <i>M.leprae</i> stimulated PBMC cultures of 28 each of freshly diagnosed patients with borderline tuberculoid (BT) and lepromatous leprosy (LL) as well as 7 healthy household contacts of leprosy patients and 4 normal skin samples.</p><p>Methodology/Principle Findings</p><p>Quantitative reverse transcribed PCR (qPCR), immuno-histochemistry/flowcytometry and ELISA were used respectively for gene expression, phenotype characterization and cytokine levels in PBMC culture supernatants. Both skin lesions as well as <i>in vitro</i> antigen stimulated PBMC showed increased percentage/mean fluorescence intensity of cells and higher gene expression for FOXP3⁺, TGF-β in lepromatous (p<0.01) as compared to tuberculoid leprosy patients. CD4⁺CD25⁺FOXP3⁺ T cells (Tregs) were increased in unstimulated basal cultures (p<0.0003) and showed further increase in <i>in vitro</i> antigen but not mitogen (phytohemaglutinin) stimulated PBMC (iTreg) in lepromatous as compared to tuberculoid leprosy patients (p<0.002). iTregs of lepromatous patients showed intracellular TGF-β which was further confirmed by increase in TGF-β in culture supernatants (p<0.003). Furthermore, TGF-β in iTreg cells was associated with phosphorylation of STAT5A. TGF-β was seen in CD25⁺ cells of the CD4⁺ but not that of CD8⁺ T cell lineage in leprosy patients. iTregs did not show intracellular IFN-γ or IL-17 in lepromatous leprosy patients.</p><p>Conclusions/Significance</p><p>Our results indicate that FOXP3⁺ iTregs with TGF-β may down regulate T cell responses leading to the antigen specific anergy associated with lepromatous leprosy.</p></div

Gene expression (Mean (ΔCt ± SD) of selected cytokines, signaling molecules and transcription factors associated with FOXP3+Treg and iTreg cells in skin lesions and <i>M.leprae</i> stimulated PBMC respectively in leprosy patients and healthy subjects.

<p>p≤0.05 was considered as significant using Mann Whitney two tailed, non parametric test. Abbreviations: LL: lepromatous leprosy, BT: borderline tuberculoid leprosy. N: skin from normal subjects undergoing cosmetic surgery. HC: healthy household contacts. Figures in parenthesis indicate number of subjects studied. Skin:</p><p>^a BT vs LL p<0.01 to 0.001;</p><p>^b LL vs N p<0.02 to 0.01.</p><p>^c BT vs N p<0.01. PBMC:</p><p>^d LLvs HC p<0.02,</p><p>^e BT vs HC p<0.001 by two tailed Mann Whitney test.</p><p>p<0.05 was considered significant.</p

IL-17 and relevant cytokines, IL-21, IL-22 , receptor IL-23R and transcription factor RORC in leprosy patients with Th phenotypes.

<p>Subjects with non polarized Th 0 showed increased expression as compared to polarized Th 1 and Th 2 in all clinical groups as shown in <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0002338#pntd-0002338-t005" target="_blank">Table 5</a>.</p><p>Mean Ct of 5 housekeeping genes varied from 21–22.9; Th1 and Th2 were defined on the basis of expression of IFN-γ and IL-4 given as Δ Ct in the upper two rows. IL-17 related gene expression was arbitrarily graded to indicate the range of expression on the basis of Δ Ct of each gene product: (−): 15 to 20 (Ct above 35 cycles was considered negative). (+): 10 to 14, (++): 7 to 9, (+++) 4 to 8. BT: borderline tuberculoid; LL: polar lepromatous leprosy. HC; healthy contacts exposed to leprosy patients to 1–2 years.</p

IL 17 producing cells belong to CD3⁺CD4⁺CCR6⁺ effector T cell lineage.

<p>A. Representative flow cytometry analysis on antigen stimulated PBMC of one each of BT and LL patients (see Materials and Methods). CD3⁺ gated CD4⁺ cells were examined for the presence of intracellular IL-17 and surface CCR6 (see Materials and Methods). As may be seen both IL-17A and IL-17F containing cells showed CCR6. The % of IL 17A/F⁺ CCR6⁺ cells was higher in BT as compared to LL as indicated in the figure. % of cells is given in the upper quadrant of the figure. B. Scattergram of BT and LL subjects showing Mean%+SD of IL-17A/F⁺CCR6⁺ cells which was significantly higher for IL-17A in BT as compared to LL as indicated by p values given in the figure. Abbreviations and legend as in <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0002338#pntd-0002338-g004" target="_blank">figure 4</a>.</p

Scattergram showing expression of chemokines MMP3, MMP13, CCL20 and CCL22 in leprosy and healthy subjects in antigen stimulated PBMC and skin.

<p>Whereas PBMC did not show differences within the leprosy groups for the chemokines (Mean ΔCt ±SD) at the site of the skin lesions MMP3 showed significantly higher expression in BT. Differential expression for the chemokines was observed between healthy skin and BT lesions for some of the chemokines ( p values given in the figures). Abbreviations and legend as in <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0002338#pntd-0002338-g002" target="_blank">figure 2</a>.</p

RORC, STAT3, SOCS1 expression in antigen stimulated PBMC and Skin lesions of leprosy and healthy subjects.

<p>A. Scattergram of Mean ΔCt ± SD of gene expression shows significant increase in RORC in healthy as compared to BT, Within leprosy types BT showed significantly higher RORC expression as compared to LL. Expression of STAT3 was similar in the 3 groups, and SOCS1 showed moderate and significance increase in BT as compared to healthy contacts as indicated by the p values in the figure. B. Phosphorylation of STAT3 is associated with intracellular IL-17 A in CD4⁺ cells as shown by multi-color flow cytometry analysis of antigen stimulated PBMC. Of the P-STAT3 cells BT showed higher % of IL-17A⁺ cells as compared to LL and healthy subjects as indicated in the upper quadrant. Abbreviations and legend as in <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0002338#pntd-0002338-g004" target="_blank">figure 4</a>.</p

Increase in FOXP3⁺, TGF-β⁺ and IL-10⁺ cells in lepromatous leprosy skin lesions.

<p>Immunohistochemistry on representative skin lesions from borderline tuberculoid (BT) and lepromatous leprosy (LL) patients. <b>A</b>. FOXP3 with inset showing detail of nuclear staining, cytoplasmic TGF-β and IL-10 respectively. Diaminobenzidine was used as chromogen after treatment with appropriate anti-human antibodies as given in <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0002639#s2" target="_blank">Materials and Methods</a>. Original magnification: 200× inset 400× <b>B</b>. Scatter diagram showing increase of cells with FOXP3⁺ TGF-β⁺ and IL-10⁺ in lepromatous leprosy (LL) as compared to tuberculoid leprosy (BT) lesions. Horizontal and vertical bars indicate Mean%±SD of positive cells of 1000 total cells. p<0.05 was considered significant by two tail Mann Whitney test. Figures in parenthesis indicate the number of subjects.</p