Influence of Hypoxemia on Lymphocytes Subpopulations in SARS-CoV-2 Pneumonia

BACKGROUND The role of lymphocytes in the response to SARS-CoV-2 infection is crucial and lymphopenia is a well-known poor prognostic factor in COVID-19. However, the influence of a hypoxemic environment on lymphocytes and their populations is not known.We aim to evaluate the influence of hypoxemia on lymphocyte populations in patients with SARS-CoV-2 pneumonia who present with lymphopenia. METHODSWe analyzed the clinical and analytical data of a prospective cohort of 338 patients with diagnosis of SARS-CoV-2 pneumonia. The microbiological diagnosis was made by RT-PCR. Hypoxemia was defined a PaO2/FiO2 value <300 and lymphopenia for the total lymphocyte count less than 1000 109/L. Statistical analysis was made using X2 and Student's t tests. RESULTSFrom an initial cohort of 338 patients with analyzed those with ABG resulting in 118 patients. 48.3% (57 cases) presented PaO2/FiO2<300 at admission. Lymphopenia was present in 75 cases (63.6%) and it was significantly associated with the presence of hypoxemia [PaO2/FiO2 280.5 (104.5) vs 328.3 (82.7);p=0.011] and high levels of ferritine [1108.4 (1530.5) vs 539 (488.9);p=0.020]. Patients with lymphopenia who presented hypoxemia showed low levels of CD4+ T lymphocytes compared to non-hypoxemic patients [339.7 (260.7) vs. 468.8 (319.5);p=0.019], however the CD8+ T lymphocyte values were not affected by the presence of hypoxemia [247.4 (339.8) vs. 239.7 (172.1);p=0.875].The presence of lymphopenia was associated with ICU admission (44% vs. 16.7%;p=0.003) and the need of mechanical ventilation (40% vs. 14.3%;p=0.004). Survival was similar between groups (29.3% vs. 16.3%;p=0.113). CONCLUSIONS In our series, the different lymphocyte subpopulations exhibit a different behavior in patients with acute hypoxemic respiratory failure: CD4+ T lymphocytes seem to be especially susceptible to hypoxemia in patients with SARSCoV- 2 pneumonia.