Alterations in CD39/CD73 axis of T cells associated with COVID-19 severity.

Purinergic signaling modulates immune function and is involved in the immunopathogenesis of several viral infections. This study aimed to investigate alterations in purinergic pathways in coronavirus disease 2019 (COVID-19) patients. Mild and severe COVID-19 patients had lower extracellular adenosine triphosphate and adenosine levels, and higher cytokines than healthy controls. Mild COVID-19 patients presented lower frequencies of CD4+ CD25+ CD39+ (activated/memory regulatory T cell [mTreg]) and increased frequencies of high-differentiated (CD27- CD28- ) CD8+ T cells compared with healthy controls. Severe COVID-19 patients also showed higher frequencies of CD4+ CD39+ , CD4+ CD25- CD39+ (memory T effector cell), and high-differentiated CD8+ T cells (CD27- CD28- ), and diminished frequencies of CD4+ CD73+ , CD4+ CD25+ CD39+ mTreg cell, CD8+ CD73+ , and low-differentiated CD8+ T cells (CD27+ CD28+ ) in the blood in relation to mild COVID-19 patients and controls. Moreover, severe COVID-19 patients presented higher expression of PD-1 on low-differentiated CD8+ T cells. Both severe and mild COVID-19 patients presented higher frequencies of CD4+ Annexin-V+ and CD8+ Annexin-V+ T cells, indicating increased T-cell apoptosis. Plasma samples collected from severe COVID-19 patients were able to decrease the expression of CD73 on CD4+ and CD8+ T cells of a healthy donor. Interestingly, the in vitro incubation of peripheral blood mononuclear cell from severe COVID-19 patients with adenosine reduced the nuclear factor-κB activation in T cells and monocytes. Together, these data add new knowledge to the COVID-19 immunopathology through purinergic regulation.

Indoleamine 2,3-dioxygenase 1 is essential for sustaining durable antibody responses.

Humoral immunity is essential for protection against pathogens, emphasized by the prevention of 2-3 million deaths worldwide annually by childhood immunizations. Long-term protective immunity is dependent on the continual production of neutralizing antibodies by the subset of long-lived plasma cells (LLPCs). LLPCs are not intrinsically long-lived, but require interaction with LLPC niche stromal cells for survival. However, it remains unclear which and how these interactions sustain LLPC survival and long-term humoral immunity. We now have found that the immunosuppressive enzyme indoleamine 2,3- dioxygenase 1 (IDO1) is required to sustain antibody responses and LLPC survival. Activation of IDO1 occurs upon the engagement of CD80/CD86 on the niche dendritic cells by CD28 on LLPC. Kynurenine, the product of IDO1 catabolism, activates the aryl hydrocarbon receptor in LLPC, reinforcing CD28 expression and survival signaling. These findings expand the immune function of IDO1 and uncover a novel pathway for sustaining LLPC survival and humoral immunity.

Immunological Profiling of COVID-19 Patients with Pulmonary Sequelae.

Cellular immunity may be involved in organ damage and rehabilitation in patients with coronavirus disease 2019 (COVID-19). We aimed to delineate immunological features of COVID-19 patients with pulmonary sequelae (PS) 1 year after discharge. Fifty COVID-19 survivors were recruited and classified according to radiological characteristics, including 24 patients with PS and 26 patients without PS. Phenotypic and functional characteristics of immune cells were evaluated by multiparametric flow cytometry. Patients with PS had an increased proportion of natural killer (NK) cells and a lower percentage of B cells than patients without PS. Phenotypic and functional features of T cells in patients with PS were predominated by the accumulation of CD4-positive (CD4+) T cells secreting interleukin 17A (IL-17A), short-lived effector-like CD8+ T cells (CD27-negative [CD27-] CD62L-), and senescent T cells with excessive secretion of granzyme B/perforin/interferon gamma (IFN-γ). NK cells were characterized by the excessive secretion of granzyme B and perforin and the downregulation of NKP30 and NKP46; highly activated NKT and γδ T cells exhibited NKP30 and TIM-3 upregulation and NKB1 downregulation in patients with PS. However, immunosuppressive cells were comparable between the two groups. The interrelationship of immune cells in COVID-19 was intrinsically identified, whereby T cells secreting IL-2, IL-4, and IL-17A were enriched among CD28+ and CD57- cells and cells secreting perforin/granzyme B/IFN-γ/tumor necrosis factor alpha (TNF-α)-expressed markers of terminal differentiation. CD57+ NK cells, CD4+Perforin+ T cells, and CD8+ CD27+ CD62L+ T cells were identified as the independent predictors for residual lesions. Overall, our findings unveil the profound imbalance of immune landscape that may correlate with organ damage and rehabilitation in COVID-19. IMPORTANCE A considerable proportion of COVID-19 survivors have residual lung lesions such as ground-glass opacity and fiber streak shadow. To determine the relationship between host immunity and residual lung lesions, we performed an extensive analysis of immune responses in convalescent patients with COVID-19 1 year after discharge. We found significant differences in immunological characteristics between patients with pulmonary sequelae and patients without pulmonary sequelae 1 year after discharge. Our study highlights the profound imbalance of immune landscape in the COVID-19 patients with pulmonary sequelae, characterized by the robust activation of cytotoxic T cells, NK cells, and γδ T cells, as well as the deficiencies of immunosuppressive cells. Importantly, CD57+ NK cells, CD4+Perforin+ T cells, and CD8+ CD27+ CD62L+ T cells were identified as the independent predictors for residual lesions.

Thymalin: Activation of Differentiation of Human Hematopoietic Stem Cells.

Thymalin is a polypeptide complex isolated from the thymus and regulating the functions of the immune system. Thymalin is effective in therapy of acute respiratory syndrome, chronic obstructive bronchitis, and other immunopathology. Thymalin increases functional activity of T lymphocytes, but the targeted molecular mechanism of its biological activity requires further study. We studied the influence of thymalin on differentiation of human hematopoietic stem cells (HSC) and expression of CD28 molecule involved in the implementation of antiviral immunity in COVID-19 infection. It was found that thymalin reduced the expression of CD44 (stem cell marker) and CD117 (molecule of the intermediate stage of HSC differentiation) by 2-3 times and increased the expression of CD28 (marker of mature T lymphocytes) by 6.8 times. This indirectly indicates that thymalin stimulated differentiation of CD117+ cells into mature CD28+T lymphocytes. It is known that in patients with severe COVID-19, the number of CD28+, CD4+, CD8+T lymphocytes in the blood decreased, which attested to a pronounced suppression of immunity. It is possible that the antiviral effect of thymalin consists in compensatory stimulation of HSC differentiation into CD28+T lymphocytes at the stage of immunity suppression in unfavorable course of viral infection. Thymalin can be considered as an immunoprotective peptide drug for the prevention of COVID-19.