Immune Cell Response of the Spleen in COVID-19

Objective. To study the morphometric characteristics and splenic immune cell response in patients with COVID-19.Material and methods. A prospective observational study included 70 patients. Of these, 45 patients admitted to the infectious diseases hospital with Coronavirus infection caused by the SARS-CoV-2 virus diagnosis were included in the COVID-19 group, and 25 patients were included in the acute respiratory viral infection (ARVI) comparison group. Spleen linear dimensions, including length, width, and thickness were assessed using ultrasound imaging, and calculations of the spleen weight and spleen weight coefficient (SWC) were obtained. Additionally leukocyte count and formula, erythrocyte sedimentation rate (ESR) were estimated, and the leukocyte index (LI) and neutrophil-to-lymphocyte ratio (NLR) were calculated.Results. Microsplenia was common in the acute period of COVID-19 with mean SWC value 1.6±0.2. In 17 (37.8%) patients the SWC varied from 1.0 to 1.5, and in 9 (20%) microsplenia was critical with SWC <1.0. Leukocyte count was lower, and ESR — higher in patients with COVID-19, compared to ARVI group (5.4±2.1×10⁹/l and 10.8±4.8×109/l, respectively P<0.00001, and ESR — 36.1±13.8 mm/h and 23.0±5.1 mm/h, respectively P=0.03). The course of COVID-19 was characterized by a slight decrease in LI — from 0.29±0.02 to 0.22±0.01 (P=0.19), and significant increase in NLR from 3.7±0.1 to 4.3±0.12 (P=0.002). Opposite trends were documented in patients with ARVI. On Day 5 since initiation of treatment LI was significantly lower in the COVID-19 vs ARVI group (0.22 [0.16; 0.39] vs. 0.48 [0.29; 0.93], P=0.003), and NLR was significantly higher (4.3 [2.5; 6.1] vs. 2.1 [0.9; 2.9], P=0.002).Conclusion. The course of coronavirus infection caused by the SARS-CoV-2 virus is characterized by significant immunological shifts. Microsplenia verified by ultrasonography stays as one of the pathognomonic signs. This phenomenon is explained by rapid «depletion» of the spleen as a secondary immune organ, and is associated with a high risk of developing acute immune deficiency.