Alterations in the CD56- and CD56+ T Cell Subsets during COVID-19.

The effectiveness of the antiviral immune response largely depends on the activation of cytotoxic T cells. The heterogeneous group of functionally active T cells expressing the CD56 molecule (NKT-like cells), that combines the properties of T lymphocytes and NK cells, is poorly studied in COVID-19. This work aimed to analyze the activation and differentiation of both circulating NKT-like cells and CD56- T cells during COVID-19 among intensive care unit (ICU) patients, moderate severity (MS) patients, and convalescents. A decreased proportion of CD56+ T cells was found in ICU patients with fatal outcome. Severe COVID-19 was accompanied by a decrease in the proportion of CD8+ T cells, mainly due to the CD56- cell death, and a redistribution of the NKT-like cell subset composition with a predominance of more differentiated cytotoxic CD8+ T cells. The differentiation process was accompanied by an increase in the proportions of KIR2DL2/3+ and NKp30+ cells in the CD56+ T cell subset of COVID-19 patients and convalescents. Decreased percentages of NKG2D+ and NKG2A+ cells and increased PD-1 and HLA-DR expression levels were found in both CD56- and CD56+ T cells, and can be considered as indicators of COVID-19 progression. In the CD56- T cell fraction, increased CD16 levels were observed in MS patients and in ICU patients with lethal outcome, suggesting a negative role for CD56-CD16+ T cells in COVID-19. Overall, our findings suggest an antiviral role of CD56+ T cells in COVID-19.

The Role of Lymphocyte Subsets, PD-1, and FAS (CD95) in COVID-19 Cancer Patients.

Lymphocytes are the main orchestrators that regulate the immune response in SARS-COV-2 infection. The exhaustion of T lymphocytes is a contributing factor to lymphopenia, which is responsible for the COVID-19 adverse outcome. However, it is still not demonstrated on a large scale, including cancer patients. Peripheral blood samples were obtained from 83 SARS-CoV2 infected cancer patients, and 29 COVID-19 infected noncancer patients compared to 28 age-matched healthy controls. Lymphocyte subsets were assessed for CD3, CD4, CD8, CD56, PD-1, and CD95 using flow cytometry. The data were correlated to the patients' clinical features, COVID-19 severity and outcomes. Lymphopenia, and decreased CD4+ T cells and CD8+ T cells were significantly observed in COVID-19 cancer and noncancer patients compared to the control group (p < 0.001, for all). There was a significantly increased expression of CD95 and PD-1 on the NK cells, CD4+ T cells, and CD8+ T cells in COVID-19 cancer and noncancer patients in comparison to the control group. The increased expression of CD95 on CD8+ T cells, as well as the increased expression of PD-1 on CD8+ T cells and NK cells are significantly associated with the severity of COVID-19 infection in cancer patients. The increased expression of CD95 and PD-1 on the CD4+ T cells, CD8+ T cells, and NK cells was observed significantly in nonsurviving patients and those who were admitted to the intensive care unit in COVID-19 cancer and noncancer patients. The increased expression of PD-1 and CD95 could be possible prognostic factors for COVID-19 severity and adverse outcomes in COVID-19 cancer and noncancer patients.

Comparison of T Lymphocyte Subsets and Natural Killer Lymphocytes in Moderate Versus Severe COVID-19 Patients.

Severe respiratory involvement that follows a process of immune dysregulation and intense cytokine production remains to be the most dreaded complication of Coronavirus Disease-2019 (COVID-19) infection. The aim of this study was to analyze T lymphocyte subsets and natural killer (NK) lymphocytes in moderate and severe cases of COVID-19 infection and assess their significance in disease severity and prognosis. Twenty moderate cases and 20 severe cases of COVID-19 were studied and compared regarding blood picture, biochemical markers, T lymphocyte population subsets, and NK lymphocytes, which were determined by flow cytometric analysis. On analyzing the flow cytometric data of T lymphocyte cells and their subsets and NK cells in two groups of COVID-19 infection (one group moderate and the other severe cases), some immature NK lymphocyte relative and absolute counts were higher in the severe patients with worse outcome and death, while some mature NK lymphocyte relative and absolute counts were depressed in both groups. Also, interleukin (IL)-6 was significantly higher in severe cases when compared to moderate cases, and there was a positive significant correlation between immature NK lymphocyte relative and absolute counts and IL-6. There was no statistically significant difference between T lymphocyte subsets (T helper and T cytotoxic) with disease severity or outcome. Some immature NK lymphocyte subsets contribute to the widespread inflammatory response that complicates severe cases of COVID-19; therapeutic approaches directed to enhancing NK maturation or drugs that block NK cell inhibitory receptors have a potential role in controlling COVID-19 induced cytokine storm.

Lymphopenia with Altered T Cell Subsets in Hospitalized COVID-19 Patients in Pune, India.

The cellular immune cell subsets affecting COVID-19 disease severity are being studied by researchers from many countries. The current study was carried out to investigate the alteration of peripheral blood mononuclear cells (PBMCs) and their subsets in hospitalized COVID-19 patients in a tertiary care center in Pune, India. The PBMCs were isolated from enrolled study participants, and flow cytometry analysis was done to assess peripheral white blood cell alterations. The lymphocyte subsets of naive, effector, central memory, and effector memory CD4+ or CD8+ T cells were then evaluated in COVID-19 patients with different disease categories and compared to healthy controls. The immunophenotypic characterization of the immune cell subset was done for 139 COVID-19 patients and 21 healthy controls. These data were evaluated based on the disease severity. A total of 139 COVID-19 patients were classified as mild (n = 30), moderate (n = 57), or severe (n = 52) cases. The decreased percentages of total lymphocytes, CD3+ T cells, CD4+ T cells, naive T cells, central memory T cells, and Natural Killer (NK) cytotoxic cells were found, and there was increase in effector T (TEf) cells and effector memory T cells in patients with severe COVID-19 compared to healthy controls. The severity of SARS-CoV-2 infection has an effect on lymphocyte subsets, resulting in reduced T memory cells and NK cells but increased TEf cells in severe cases. Clinical Trial Registration: CTRI ID-CTRI/2021/03/032028.

Kinetics of Immune Subsets in COVID-19 Patients Treated with Corticosteroids.

RATIONALE: Changes in anti-SARS-CoV-2 defense immune subsets in patients treated with dexamethasone (DXM) for severe COVID-19 and their relation to disease outcomes are poorly understood. METHODS: Blood-lymphocyte subsets of 110 hospitalized COVID-19 patients were prospectively examined. A first sample was taken at enrollment and a second one 7-10 days later. Total B-, T-lymphocytes, CD4+, CD8+, T-regulatory (Treg), Natural-Killer (NK) and NK T-cells were counted using flow cytometry. RESULTS: At enrollment, patients with respiratory failure, characterized by DXM failure (intubation/death) or DXM success (hospital discharge) exhibited significantly fewer CD3+, CD4+ and CD8+ cells and B-lymphocytes compared to the control group (no respiratory failure/no DXM). At the time of treatment completion, the DXM-failure group exhibited significantly fewer CD3+, CD4+ and CD8+ cells, memory CD4+ and CD8+ T-lymphocytes, compared to the control and the DXM-success groups and fewer activated CD4+ T-lymphocytes, Tregs and NK cells compared to the control group. At the time of treatment completion, the number of all investigated lymphocyte subsets increased in the DXM-success group and was similar to those of the control group. NK cells significantly decreased over time in the DXM-failure group. CONCLUSION: The lymphocyte kinetics differ between DXM-treated and control COVID-19 patients and are associated with clinical outcomes.

Circulating effector γδ T cell populations are associated with acute coronavirus disease 19 in unvaccinated individuals.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection causes severe coronavirus disease 2019 (COVID-19) in a small proportion of infected individuals. The immune system plays an important role in the defense against SARS-CoV-2, but our understanding of the cellular immune parameters that contribute to severe COVID-19 disease is incomplete. Here, we show that populations of effector γδ T cells are associated with COVID-19 in unvaccinated patients with acute disease. We found that circulating CD27neg CD45RA+ CX3CR1+ Vδ1effector cells expressing Granzymes (Gzms) were enriched in COVID-19 patients with acute disease. Moreover, higher frequencies of GzmB+ Vδ2+ T cells were observed in acute COVID-19 patients. SARS-CoV-2 infection did not alter the γδ T cell receptor repertoire of either Vδ1+ or Vδ2+ subsets. Our work demonstrates an association between effector populations of γδ T cells and acute COVID-19 in unvaccinated individuals.

The dynamics of γδ T cell responses in nonhuman primates during SARS-CoV-2 infection.

Although most SARS-CoV-2 infections are mild, some patients develop systemic inflammation and progress to acute respiratory distress syndrome (ARDS). However, the cellular mechanisms underlying this spectrum of disease remain unclear. γδT cells are T lymphocyte subsets that have key roles in systemic and mucosal immune responses during infection and inflammation. Here we show that peripheral γδT cells are rapidly activated following aerosol or intra-tracheal/intra-nasal (IT/IN) SARS-CoV-2 infection in nonhuman primates. Our results demonstrate a rapid expansion of Vδ1 γδT cells at day1 that correlate significantly with lung viral loads during the first week of infection. Furthermore, increase in levels of CCR6 and Granzyme B expression in Vδ1 T cells during viral clearance imply a role in innate-like epithelial barrier-protective and cytotoxic functions. Importantly, the early activation and mobilization of circulating HLA-DR+CXCR3+ γδT cells along with significant correlations of Vδ1 T cells with IL-1Ra and SCF levels in bronchoalveolar lavage suggest a novel role for Vδ1 T cells in regulating lung inflammation during aerosol SARS-CoV-2 infection. A deeper understanding of the immunoregulatory functions of MHC-unrestricted Vδ1 T cells in lungs during early SARS-CoV-2 infection is particularly important in the wake of emerging new variants with increased transmissibility and immune evasion potential.

COVID-19 vaccination influences subtypes of γδ-T cells during pregnancy.

Up to now, there has been insufficient clinical data to support the safety and effects of vaccination on pregnancy post COVID-19 vaccination. The γδ-T cells are considered an important component in the immune system to fight against viral infection and exhibit critical roles throughout the pregnancy period. However, the immunological roles of γδ-T cells in pregnant women with the COVID-19 vaccination remain unclear. Therefore, the objective of this study is to investigate the alteration of frequency and expression pattern of activation receptors and inhibitory receptors in γδ-T cell and its subsets in peripheral blood samples collected from non-pregnant vaccinated women, vaccinated pregnant women, and unvaccinated pregnant women. Our findings indicated that the frequency of CD3+γδ-T+ cells is lower in vaccinated pregnant women than in unvaccinated pregnant women. But no significant difference was found in the frequency of CD3+γδ-T+ cells between non-pregnant vaccinated women and vaccinated pregnant women. In addition, there were no significant differences in the frequencies of CD3+γδ-T+Vδ1+T cells, CD3+γδ-T+Vδ2+T cells, CD3+γδ-T+Vδ1-Vδ2-T cells, and Vδ1+T cell/Vδ2+T cell ratio between the pregnant women with or without COVID-19 vaccination. Similar results were found after comparing non-pregnant and pregnant women who received the COVID-19 vaccine. However, there was a significant difference in the fraction of Vδ1-Vδ2-T cells in CD3+γδ-T+ cells between non-pregnant vaccinated women and vaccinated pregnant women. The frequency of NKG2D+ cells in Vδ2+T cells was not significantly different in the vaccinated pregnant women when compared to that in unvaccinated pregnant women or non-pregnant vaccinated women. But the percentage of NKG2D+ cells in Vδ1+T cells was the lowest in pregnant women after COVID-19 vaccination. Furthermore, down-regulation of NKP46 and NKP30 were found in Vδ2+T and Vδ1+T cells in the vaccinated pregnant women, respectively. After the vaccination, up-regulation of PD-1 expression in Vδ1+T cells and Vδ2+T cells indicated γδ-T cells could respond to COVID-19 vaccination and display an exhausted phenotype following activation. In conclusion, COVID-19 vaccination influences subtypes of γδ-T cells during pregnancy, but the side effects might be limited. The phenotypical changes of Vδ1+T cells and Vδ2+T cells will be a promising predictor for evaluating the clinical outcome of the COVID-19 vaccine.

Defying convention in the time of COVID-19: Insights into the role of γδ T cells.

Coronavirus disease 2019 (COVID-19) is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). COVID-19 is a complex disease which immune response can be more or less potent. In severe cases, patients might experience a cytokine storm that compromises their vital functions and impedes clearance of the infection. Gamma delta (γδ) T lymphocytes have a critical role initiating innate immunity and shaping adaptive immune responses, and they are recognized for their contribution to tumor surveillance, fighting infectious diseases, and autoimmunity. γδ T cells exist as both circulating T lymphocytes and as resident cells in different mucosal tissues, including the lungs and their critical role in other respiratory viral infections has been demonstrated. In the context of SARS-CoV-2 infection, γδ T cell responses are understudied. This review summarizes the findings on the antiviral role of γδ T cells in COVID-19, providing insight into how they may contribute to the control of infection in the mild/moderate clinical outcome.

Phenotypical and Functional Alteration of γδ T Lymphocytes in COVID-19 Patients: Reversal by Statins.

(1) Background: statins have been considered an attractive class of drugs in the pharmacological setting of COVID-19 due to their pleiotropic properties and their use correlates with decreased mortality in hospitalized COVID-19 patients. Furthermore, it is well known that statins, which block the mevalonate pathway, affect γδ T lymphocyte activation. As γδ T cells participate in the inflammatory process of COVID-19, we have investigated the therapeutical potential of statins as a tool to inhibit γδ T cell pro-inflammatory activities; (2) Methods: we harvested peripheral blood mononuclear cells (PBMCs) from COVID-19 patients with mild clinical manifestations, COVID-19 recovered patients, and healthy controls. We performed ex vivo flow cytometry analysis to study γδ T cell frequency, phenotype, and exhaustion status. PBMCs were treated with Atorvastatin followed by non-specific and specific stimulation, to evaluate the expression of pro-inflammatory cytokines; (3) Results: COVID-19 patients had a lower frequency of circulating Vδ2+ T lymphocytes but showed a pronounced pro-inflammatory profile, which was inhibited by in vitro treatment with statins; (4) Conclusions: the in vitro capacity of statins to inhibit Vδ2+ T lymphocytes in COVID-19 patients highlights a new potential biological function of these drugs and supports their therapeutical use in these patients.

Rare Case of Persistently Depressed T Lymphocyte Subsets After SARS-CoV-2 Infection.

BACKGROUND On rare occasions, viral infections are known to also depress immune cell lines, further worsening clinical outcomes. We describe a patient who presented 3 weeks after recovery from mild COVID-19 disease with clinical features of an atypical pneumonia and was found to have a low CD4+ T-cell count. CASE REPORT An 82-year-old man with a past medical history of coronary artery disease, rheumatoid arthritis, gout, hypertension, and atrial fibrillation presented with a 1-week history of progressively worsening shortness of breath and cough. He was noted to have recovered from mild SARS-CoV-2 infection 3 weeks prior to his current presentation and had been at his baseline level of health following infection. A T cell subset panel was obtained, which revealed an absolute CD3 count of 92 (reference range 840-3060), absolute CD4 count of 52 (reference range 500-1400), absolute CD8 count of 37 (reference range 180-1170), and a normal CD4: CD8 ratio. He was subsequently started on atovaquone for pneumocystis jiroveci pneumonia prophylaxis. CONCLUSIONS This case highlights the need for a high index of suspicion for lymphocyte depletion in older patients with multiple comorbidities who present during or after SARS-CoV-2 infection with atypical symptoms that are suggestive of immunosuppression. In such instances, there should be a low threshold to start prophylactic therapy for possible opportunistic infections.

Characterization of memory T cell subsets and common γ-chain cytokines in convalescent COVID-19 individuals.

T cells are thought to be an important correlates of protection against SARS-CoV2 infection. However, the composition of T cell subsets in convalescent individuals of SARS-CoV2 infection has not been well studied. The authors determined the lymphocyte absolute counts, the frequency of memory T cell subsets, and the plasma levels of common γ-chain in 7 groups of COVID-19 individuals, based on days since RT-PCR confirmation of SARS-CoV-2 infection. The data show that both absolute counts and frequencies of lymphocytes as well as, the frequencies of CD4+ central and effector memory cells increased, and the frequencies of CD4+ naïve T cells, transitional memory, stem cell memory T cells, and regulatory cells decreased from Days 15-30 to Days 61-90 and plateaued thereafter. In addition, the frequencies of CD8+ central memory, effector, and terminal effector memory T cells increased, and the frequencies of CD8+ naïve cells, transitional memory, and stem cell memory T cells decreased from Days 15-30 to Days 61-90 and plateaued thereafter. The plasma levels of IL-2, IL-7, IL-15, and IL-21-common γc cytokines started decreasing from Days 15-30 till Days 151-180. Severe COVID-19 patients exhibit decreased levels of lymphocyte counts and frequencies, higher frequencies of naïve cells, regulatory T cells, lower frequencies of central memory, effector memory, and stem cell memory, and elevated plasma levels of IL-2, IL-7, IL-15, and IL-21. Finally, there was a significant correlation between memory T cell subsets and common γc cytokines. Thus, the study provides evidence of alterations in lymphocyte counts, memory T cell subset frequencies, and common γ-chain cytokines in convalescent COVID-19 individuals.

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's 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.

Reduced Counts of Various Subsets of Peripheral Blood T Lymphocytes in Patients with Severe Course of COVID-19.

This study was intended to define T lymphocyte subsets in different clinical groups of COVID-19-infected patients to explore the interaction between T cell-mediated immune response and the severity of COVID-19 course. Lymphopenia in patients with severe COVID-19 was found. In patients with severe COVID-19 course, the absolute counts of CD3+, CD4+, and CD8+ T lymphocytes at admission were lower than on day 14 after discharge. Further analysis showed that the older were the patients with COVID-19, the more likely they developed severe infection. The results confirmed the significance of T lymphocytes in the clearance of the COVID-19.

Short and long-term immune changes in different severity groups of COVID-19 disease.

BACKGROUND: There are limited data on short- versus long-term changes in adaptive immune response across different COVID-19 disease severity groups. METHODS: A multicenter prospective study of 140 adult patients with COVID-19 (a total of 325 samples) were analyzed for inflammatory markers and lymphocyte subsets at presentation, week 2, and week 24. RESULTS: Inflammatory markers at presentation were higher in the critical/severe than in moderate and mild groups. A predominance of memory B cell response in the mild and moderate group was noted by week 2. In contrast, the immune system in the severe/critical group was dysfunctional, with expansion of exhausted CD8+ T cells and atypical memory B cells. By 24 weeks, there was a possible trend of normalization. CONCLUSION: There was substantial difference in the degree of inflammation and distribution of different B and T cell subsets in the different disease severity groups. Despite the initial dysfunctional immune response in the severe/critical group, a comparable memory B and CD8+ T cell responses to the mild group was achieved at 24 weeks.

T helper profile in pregnant women recovered from COVID-19.

T helper (Th) cell subsets play distinct and important roles during pregnancy. This work was focused on investigating the Th and cytokine profile in pregnant women recovered from COVID-19. To this aim, the frequency of Th1, Th2, Th17 subsets and the level of associated cytokines were analysed in pregnant women recovered from COVID-19 and in matched non-pregnant women. Principal component analysis highlighted a significant impact of pregnancy on Th profile with an increase of ex-Th17 subset and a parallel decrease of Th1 population. These modulations may participate in both preserving the pregnancy and reducing the risk of severe infection.

T Cell Senescence by Extensive Phenotyping: An Emerging Feature of COVID-19 Severity.

OBJECTIVE: To identify the potential prognostic value of lymphocyte subsets in COVID-19 patients, where lymphopenia is a common finding. METHODS: In 353 COVID-19 inpatients and 40 controls T cell subsets with markers of senescence and exhaustion were studied by flow cytometry. RESULTS: In severe illness, total lymphocytes B, NK, and all T subsets were dampened. Senescent CD4+, but mainly CD8+ T cells, increased in patients with respect to controls. The most significant index predicting fatal outcome was neutrophils/CD3+ T ratio. CONCLUSION: In conclusion, an altered T cell pattern underlies COVID-19 severity and is involved in predicting the outcome.

COVID-19 Infection in Patients with Comorbidities: Clinical and Immunological Insight.

AIM: Our study's objectives were to study the clinical and laboratory characteristics that may serve as biomarkers for predicting disease severity, IL-10 levels, and frequencies of different T cell subsets in comorbid COVID-19 patients. METHODS: Sixty-two hospitalized COVID-19 patients with comorbidities were assessed clinically and radiologically. Blood samples were collected to assess the T lymphocyte subsets by flow cytometry and IL-10 levels by ELISA. RESULTS: The most common comorbidities observed in COVID-19 patients were diabetes mellitus (DM), hypertension, and malignancies. Common symptoms and signs included fever, cough, dyspnea, fatigue, myalgia, and sore throat. CRP, ferritin, D dimer, LDH, urea, creatinine, and direct bilirubin were significantly increased in patients than controls. Lymphocyte count and CD4+ and CD8+ T-cells were significantly decreased in comorbid COVID-19 patients, and CD25 and CD45RA expression were increased. CD4+ and CD8+ regulatory T cells (Tregs) and IL-10 levels were significantly decreased in patients. CONCLUSIONS: Many parameters were found to be predictive of severity in the comorbid patients in our study. Significant reductions in the levels and activation of CD4+ and CD8+ T-cells were found. In addition, CD4+ and CD8+ Tregs were significant decreased in patients, probably pointing to a prominent role of CD8+ Tregs in dampening CD4+ T-cell activation.

COVID-19 and the role of cytokines in this disease.

Studies have shown that SARS-CoV-2 has the ability to activate and mature proinflammatory cytokines in the body. Cytokine markers are a group of polypeptide signalling molecules that can induce and regulate many cellular biological processes by stimulating cell receptors at the surface. SARS-CoV-2 has been shown to be associated with activation of innate immunity, and an increase in neutrophils, mononuclear phagocytes, and natural killer cells has been observed, as well as a decrease in T cells including CD4+ and CD8. It is noteworthy that during the SARS-CoV-2 infection, an increase in the secretion or production of IL-6 and IL-8 is seen in COVID-19 patients along with a decrease in CD4+ and CD8+ and T cells in general. SARS-CoV-2 has been shown to significantly increase Th2, Th1/Th17 cells and antibody production in the body of patients with COVID-19. Specific immune profiles of SARS-CoV-2 infection can lead to secondary infections and dysfunction of various organs in the body. It has been shown that Interleukins (such as IL-1, IL-4, IL-6, IL-7, IL-10, IL-12, IL-17, and IL-18), IFN-γ, TNF-α,TGF-ß and NF-κB play major roles in the body's inflammatory response to SARS-CoV-2 infection. The most important goal of this review is to study the role of inflammatory cytokines in COVID-19.

Immunophenotyping of lymphocytes and monocytes and the status of cytokines in the clinical course of Covid-19 patients.

Lymphopenia, T cell subgroup changes, and cytokine level differences are important in the early diagnosis and treatment of Covid-19 cases and similar pandemics. We aimed to investigate the T cell, monocyte subgroups, and cytokine differences according to disease severity. A total of 46 volunteers were included in the study. According to disease status, there were three groups (control, mild, and severe). The age, gender, smoking status, temperature, heart rate and oxygen saturation, complete blood count, C-reactive protein (CRP) was noted, and flow cytometric analyses were performed for T cell and monocyte subgroups, and cytokine levels. Temperature, heart rate, SPO2 , white blood cell (WBC), lympocyte count, trombocyte count, neutrophil/lymphocyte ratio, D-dimer and CRP levels, lymphocyte %, lymphocyte/monocyte rate, monocyte subtypes (%), CD3+ , CD4+ , CD8+ cell counts, interleukin (IL)-1ß, TNF-alpha, monocyte chemoattractant protein (MCP)-1, IL-6, IL-8, IL-10, IL-18, IL-23 were significantly different between groups. CRP, IL-8, neutrophil/lymphocyte ratio, NK cells (%) have positive correlation and negative correlation was observed at lymphocyte (count), lymphocyte (%), lymphocyte/monocyte, classical monocyte (%), lymphocyte (count), CD3+ (count), CD4+ (count). As conclusion, lymphocyte (%), Lymphocyte (count), CRP levels, CD3+ and CD4+ cell counts strongly correlate with disease severity are valuable parameters for determining the prognoses of Covid-19.