Evidence of Abnormally Low Lymphocyte-To-Monocyte Ratio In COVID-19-Induced Severe Acute Respiratory Syndrome

Abstract

It is known that lung injury due to COVID-19 responsible for the respiratory distress would mainly depend on host inflammatory response, depending on the excessive production of inflammatory cytokines, such as IL-6, and TNF-alpha, rather than direct virus-induced tissue damage, as well as for other forms of respiratory distress. Moreover, it is known that the inflammatory cytokines may induce profound changes in the behavior of the hematic cells, namely neutrophils, monocytes, and lymphocytes, with a following enhanced tissue infiltration by their inflammatory cells. According to the data available up to now, IL-6 and TNF-alpha would be the main cytokines involved in determining COVID-19-induced lung injury, as well as in other coronavirus infections, and most in general in all conditions of respiratory distress. Since it is known that the functionlessness of the whole immune system is namely depending on the interactions between lymphocyte and macrophage system, a preliminary study was planned to analyze the lymphocyte-to-monocyte ratio (LMR) in COVID-19 infective disease. The study included 17 consecutive patients, who underwent ventilator therapy for COVID-19-induced respiratory distress, and 100 healthy subjects, as a control group. Lymphocytopenia and monocytosis occurred in 14/17 (82%) and in 8/17(47%), respectively. Then, abnormally low values of LMR was found in 12/17 (71%) patients, and LMR men values observed in patients were significantly lower than in control (P<0.001). Therefore, by reflecting the interactions between lymphocyte and monocyte-macrophage systems, LMR could constitute a simple and less expensive biomarker to monitor the clinical evolution of COVID-19 infection.