Lymphocyte B Subtypes in Peripheral Blood: A Prognostic Biomarker for COVID-19 Patients.

BACKGROUND: In view of the scientific gap in knowledge of the involvement of the B-cell compartment and clinical prognostic in SARS-CoV-2 infection, this work aims to evaluate the B-cell subsets and the presence of specific IgM and IgG, as well as neutralizing antibodies against SARS-CoV-2, in unvaccinated patients diagnosed with COVID-19. METHODS: This study included 133 patients with COVID-19. Cellular components were assessed by flow cytometry, and immunoglobulin levels and reactivity were measured by indirect enzyme-linked immunosorbent assay. RESULTS: Our results showed no changes in less differentiated B cells. However, non-switched memory B cells (NS-MBCs) and class-switched memory B cells (CS-MBCs) were reduced in the patients with moderate disease. Also, plasmablasts and double-negative (DN) or "atypical" memory B cells were increased in groups of patients with moderate to critical conditions. In addition, the production of IgM, IgG, and neutralizing antibodies against SARS-CoV-2 demonstrated a positive correlation between the positivity of antibodies against SARS-CoV-2 and disease severity. Besides being related to the development of a more severe course of the disease, the increase in DN B-cell count also contributed to a poorer disease outcome in patients with a higher percentage of these cells. On the other hand, we observed an increase in the absolute number of CS-MBCs in patients with greater chances of survival. CONCLUSIONS: This study demonstrates that the B-cell compartment may contribute to the development of clinical symptoms of COVID-19, with changes in B-cell subset counts linked to disease course and patient prognosis.

T cell maturation is significantly affected by SARS-CoV-2 infection.

Coronavirus disease 2019 (COVID-19) is a respiratory tract infection caused by the new severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). An adequate T cell response is essential not only for fighting disease but also for the creation of immune memory. Thus, the present study aims to evaluate the T cells of patients with moderate, severe and critical COVID-19 not only at the time of illness but also 2 months after diagnosis to observe whether changes in this compartment persist. In this study, 166 COVID-19 patients were stratified into moderate/severe and critical disease categories. The maturation and activation of T cells were evaluated through flow cytometry. In addition, Treg cells were analysed. Until 15 days after diagnosis, patients presented a reduction in absolute and relative T lymphocyte counts. After 2 months, in moderate/severe patients, the counts returned to a similar level as that of the control group. In convalescent patients who had a critical illness, absolute T lymphocyte values increased considerably. Patients with active disease did not show differentiation of T cells. Nonetheless, after 2 months, patients with critical COVID-19 showed a significant increase in CD4+ EMRA (CD45RA+ effector memory) T lymphocytes. Furthermore, COVID-19 patients showed delayed T cell activation and reduced CD8+ suppressor T cells even 2 months after diagnosis. A reduction in CD4+ Treg cells was also observed, and their numbers returned to a similar level as that of healthy controls in convalescent patients. The results demonstrate that COVID-19 patients have a delayed activation and differentiation of T cells. In addition, these patients have a great reduction of T cells with a suppressor phenotype.

The relationship between peripheral immune response and disease severity in SARS-CoV-2-infected subjects: A cross-sectional study.

Coronavirus disease 2019 (COVID-19) is a respiratory infection caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and marked by an intense inflammatory response and immune dysregulation in the most severe cases. In order to better clarify the relationship between peripheral immune system changes and the severity of COVID-19, this study aimed to evaluate the frequencies and absolute numbers of peripheral subsets of neutrophils, monocytes, and dendritic cells (DCs), in addition to quantifying the levels of inflammatory mediators. One hundred fifty-seven COVID-19 patients were stratified into mild, moderate, severe, and critical disease categories. The cellular components and circulating cytokines were assessed by flow cytometry. Nitric oxide (NOx) and myeloperoxidase (MPO) levels were measured by colourimetric tests. COVID-19 patients presented neutrophilia, with signs of emergency myelopoiesis. Alterations in the monocytic component were observed in patients with moderate to critical illness, with an increase in classical monocytes and a reduction in nonclassical monocytes, in addition to a reduction in the expression of HLA-DR in all subtypes of monocytes, indicating immunosuppression. DCs, especially plasmacytoid DCs, also showed a large reduction in moderate to critical patients. COVID-19 patients showed an increase in MPO, interleukin (IL)-12, IL-6, IL-10, and IL-8, accompanied by a reduction in IL-17A and NOx. IL-10 levels ≥14 pg/ml were strongly related to the worst outcome, with a sensitivity of 78·3% and a specificity of 79·1%. The results of this study indicate the presence of systemic effects induced by COVID-19, which appear to be related to the pathophysiology of the disease, highlighting the potential of IL-10 as a possible prognostic biomarker for COVID-19.