Morphological and immunohistochemical characteristics of changes in the bronchopulmonary lymph nodes in patients with a new COVID-19 coronavirus infection (based on autopsy results)

Background: Research into the pathogenesis and morphogenesis of new coronavirus infection (COVID-19) is currently a hot topic that requires the accumulation, management and analysis of the data. Understanding the mechanisms of the disease and their characteristics would help to improve diagnostic quality, treatment efficacy and reduce mortality.

Aim: To identify morphological and immunohistochemical characteristics of the bronchopulmonary lymph node tissues in autopsied patients with COVID-19.

Materials and methods: The study was carried out on 44 autopsy samples from patients who were hospitalized and died from the new coronavirus infection COVID-19 in the Moscow Regional Research and Clinical Institute. Macroscopic, histological, and immunohistochemical assessment methods were used.

Results: We found stereotypical abnormalities in the morphology and cellular composition of the lymphoid tissue depending on the duration of the disease. These included signs of B-cell-mediated immunity suppression manifested by a decrease in the number and size of lymphoid follicles and occurs at latest after 7 days from the onset of the disease. In the patients with the disease duration of up to 14 days, the T-cell pool of the lymph nodes is represented mainly by CD4+ T-lymphocytes. With longer duration of the disease, there is a gradual increase in the number of lymphoid follicles and their sizes, with changes of the CD4+ to CD8+ T-cell ratio towards higher CD8+ counts. After 21 days of the disease, the CD4+ to CD8+ ratio levels off.

Conclusion: The results obtained indicate a direct damaging effect of SARS-CoV-2 on the lymph node tissues of the bronchopulmonary group. The possibility of secondary transient immune deficiency and infectious  complications in patients with a new coronavirus infection is discussed.