Flow Cytometric Analysis of Lymphocyte Subsets of Covid-19 Patients from A Single Centre in Turkey

Abstract

Background:
 Lymphocyte counts have been shown to negatively correlate with the severity and different outcomes in Covid-19. The aim of this single centre study is to analyse the distribution of lymphocyte subsets in response to SARS-CoV-2 infection and its relation to the severity, course and prognosis of the disease.
 Methods:
 Blood samples were obtained from 67 consecutive patients between April 2020 and July 2020. Data on other laboratory parameters, and clinical course were collected retrospectively from patient files and patints were defined to have as severe or non-severe (mild/moderate) disease. Leukocyte subsets to be studied were identified by using flow cytometric analysis. Patients were allocated into 3 groups based on the day of blood sample collection for the flow cytometric analysis: Days 0-7, Days 8-14 and Days >14 as Group I, Group II and Group III, respectively. In 10 available of 67 patients an additional flow cytometric analysis was done 7-10 days after the initial sampling.
 Results:
 Lower total lymphocyte, CD3 positive, CD4 positive and B-cell counts were identified in severe infection compared to non-severe infection group which were also correlated with high serum CRP, D-dimer and ferritin levels. NK and monocyte counts were not different between the two groups. Activation markers CD38 and HLA-DR on CD4 and CD8 positive lymphocytes also were not different in either group. 
 Conclusion:
 CD3 and CD4 lymphopenia were lower in accordance with previous studies and were associated with severe disease. The expectancy of high activation markers was not met. Future studies with detailed subgroup analyses at different time-points, and immune profiling after vaccination as well as during new infection in vaccinated patients will shed more light on our general knowledge of the immune response to COVID-19 and viruses in general.