COVID-19, spreading rapidly all over the world, causes serious morbidity and mortality. In severe COVID-19 infections, after pulmonary inflammation, cardiovascular organ failure, cytokine storm, hemophagocytosis, septic shock, develops due to uncontrolled hypoxia, and isolated organ failure turns into multi-organ failure. It is noteworthy that it causes lymphopenia in patients. In studies conducted, the effects of Covid-19 on the immune system were evaluated with limited parameters. In addition, no study evaluating the effect of this disease on the immune system has been published in our country.

The causative agent of coronavirus 2019 (COVID-19) disease, which started in Wuhan province of China in December 2019, was severe acute respiratory failure syndrome coronavirus 2 (SARS-CoV-2), which quickly spread all over the world and caused a pandemic. COVID-19 can cause death with symptoms such as fever, cough, muscle pain, shortness of breath, and pneumonia (1). Pulmonary pathology of COVID-19 is diffuse alveolar damage, focal reactive hyperplasia of pneumocytes with patchy inflammatory cells, intravascular thrombosis, monocyte, macrophage and lymphocyte infiltration into pulmonary spaces. Severe infiltration of pulmonary tissue affects alveolar gas exchange. In addition, cardiovascular morbidity, tachyarrhythmia and thromboembolic events are observed in 1/5 of the hospitalized patients with troponin elevation, which is closely related to mortality. In severe COVID-19 infections, after pulmonary inflammation, cardiovascular organ failure, cytokine storm, hemophagocytosis, septic shock, develops due to uncontrolled hypoxia, and isolated organ failure turns into multi-organ failure.

It is noteworthy that it causes lymphopenia in patients. In the studies conducted, the effects of Covid-19 on the immune system and the determination of cell subgroups were performed with limited parameters. No studies have been conducted on PDL-1, one of the immune control points. In addition, no study evaluating the effect of this disease on the immune system with wide parameters has been published in our country.

We aimed to study CD3 (+) lymphocytes, CD4 (+) lymphocytes, CD 8 (+) lymphocytes, CD 3(-)/CD16 (+) NK cell ratio, CD14 (+) lymphocytes, and HLA-DR positivity on CD14 (+) cells at Covid-19 and healthy volunteers.

Inclusion Criteria:

• Patients with Covid 19 PCR (+) results

Exclusion Criteria:

• Cancer Patients
• Patients with known immunodeficiency
• Pregnancy

Patients who admitted to the emergency department with the complaint of respiratory failure, lymphopenia in blood tests and Covid 19 (+) in the PCR tests are case group.

Also healty volunteers who don't have complaint of respiratory failure, lymphopenia in blood tests and Covid 19 (-) in the PCR tests are control group.