Morphological characteristics of the lungs in COVID-19 patients with diseases of the blood system

Aim: To study the variants of morphological changes in the lung using material from pathological autopsies of patients with blood diseases who died of COVID-19. Materials and Methods: A retrospective morphological analysis of histological preparations of lung tissue was performed in a cohort of patients with blood diseases, using standard histological staining with haematoxylin and eosin and assessment of the state of alveolocytes of type 1 and 2, Mallory and Van Gieson staining to assess the state of connective tissue. The leukocyte profile of the lung tissue was studied by immunohistochemical analysis using antibodies of differentiation clones (CD) 4, 8, 20, 34 and collagen type IV. Results: 22 fatal cases of patients with blood diseases who died of COVID-19 were analysed (13 men and 9 women); the mean age was 63 years. The selected cohort included non-neoplastic (myelodysplastic syndrome with multilineage dysplasia) and neoplastic blood disorders (chronic lymphocytic leukaemia, acute myeloid leukaemia, acute lymphoblastic leukaemia, multiple myeloma). Morphometric analysis revealed certain differences in the condition of the lung tissue. In the group with myelodysplasia, the morphological picture of lung tissue damage in COVID-19 is characterised by the destruction of alveolar tissue, the presence of single alveolocytes and the absence of neutrophils and macrophages. In chronic lymphocytic leukaemia, a disruption in the formation of hyaline membranes and the development of mycetomas, the appearance of lymphocytes of different sizes were observed. In lymphoma, the development of thrombus formation was observed against a background of decollagenisation of the vessel wall. In multiple myeloma, multinucleated alveolocytes formed as a result of viral metamorphosis were seen. In untreated patients, blasts were detected at the onset of acute myeloid leukaemia. Despite the diversity of the cohort, the immune response showed a universal response in the form of disappearance of CD4 and expression of CD8 and CD34 leukocytes in all cases considered. An individual feature in multiple myeloma was the positive expression of CD20+ leukocytes in lung tissue. Conclusions: Lung damage in COVID-19 is characterised by differences in the state of the morphological picture depending on the oncohematological disease and the universality of the immune response, with a difference in patients with multiple myeloma in the form of increased expression of CD20+, probably due to the pathogenesis of myeloma and the accumulation of pathological clones of leukocytes.