Early phases of COVID-19 are characterized by a reduction of lymphocyte populations and the presence of atypical monocytes

Background Severe acute respiratory syndrome coronavirus 2 is a recently discovered pathogen responsible of coronavirus disease 2019 (COVID-19). The immunological changes associated with this infection are largely unknown. Methods We evaluated the peripheral blood mononuclear cells profile of 63 patients with COVID-19 at diagnosis and the presence of association with inflammatory biomarkers and 28-days mortality. Results Lymphocytopenia was present in 51 of 63 (80.9%) patients. This reduction was mirrored also on CD8+ lymphocytes (128 cells/μL), natural killer cells (67 cells/μL) and natural killer T cells (31 cells/μL). Monocytes were preserved in total number but displayed a subpopulation composed mainly of cells with a reduced expression of both CD14 and HLA-DR. A direct correlation was found between serum values of IL-6 and the frequency of Th2 lymphocytes (R=0.17; p =0.04) but not with the monocytes count (R=0.01; p =0.60). Patients who died in the 28 days from admission (N=10, 15.9%), when compared to those who did not, displayed lower mean values of CD3+ ( p =0.028) and CD4+ cells ( p =0.042) and higher mean percentages of CD8+/CD38+/HLA-DR+ lymphocytes ( p =0.026). Conclusions The early phases of COVID-19 are characterized by lymphocytopenia, predominance of Th2 lymphocytes and less immunocompetent monocytes, which include atypical mononuclear cells. eTOC -At diagnosis patients with COVID-19 have lymphocytopenia -Monocytes with both normal or altered scatter properties display a reduced expression of CD14 and HLA-DR in most of COVID-19 patients -Patients who die in the 28 days from admission have lower values of CD3+ and CD4+ cells and higher percentages of activated CTL cells compared to those who survive