УДК 616.24-002-053.2:578.834](0.083.96)

Objective —    to    determine    the    features    of    pathogenesis    in    patients    with    the    pulmonary  form    of    SARS-CoV-2.    To     establish,     based     on     clinical     examination     data     and     electron     microscopy,     that     vasculitis     of     the     respiratory    
system    is    the    main    pathophysiological    and    pathomorphological    factor    in    lung    tissue    damage    in    COVID-19.
Materials and methods.    A    total    of    692    patients    aged    18    to    73    years    with    severe    SARS-CoV-2    were    examined.    The    control    group    consisted    of    50    patients    (25    women    and    25    men)    aged    25—70    years    with    a    moderately    severe    clinical     course     of     SARS-CoV-2.     58     patients     underwent     immunological     tests,     which     included     the     study    of    O-lymphocytes    and    D-lymphocytes,    circulating    small    and    large    immune    complexes.    A  group    of    30    people    who    died     of     COVID-19     pneumonia     underwent     a     pathohistological     examination     of     tissue     samples.     A     group     of    10    people    who    died    of    COVID-19    pneumonia    underwent    electron    microscopic    examination    of    tissue    samples.
Results and discussion. Immunological    examination    revealed    an    increase    in    the    number    of    O-lymphocytes    (53.3    ±    1.3),    an    increase    in    the    number    of    D-lymphocytes    (4.9    ±    0.7),   which    highlights    the    impairment    of   T-cells    of    immunity;    the    predominance    of    the  total   mass    of    an    increased    level    of    small    CICs    (71.3    ±    2.5),    which    indicates    a    particularly    «malignant»    autoimmune    component    with    damage    to    the    connective    tissue    structure,    primarily    the    vessels    of    the    lungs,    and    therefore    the    vessels    of    epithelial    organs,    and    an    increase    in    the    number    of    large    CICs,    which    explains    the    material    basis    of    allergic    complications    that    accompany    the    severe    course    of    
SARS.    Ultrastructural    electron    microscopic    examination    of    the    respiratory    tract    of    patients    who    died    from    respiratory     failure     in     COVID-19     revealed     the     development     of     degenerative     changes     in     the     capillaries     and    endothelium,     characterised     by     the     expansion     of     the     tubules     of     the     granular     endoplasmic     reticulum,     the    destruction     of     ribosomes,     the     appearance     of     vacuoles     in     the     cytoplasm     surrounded     by     a    double-contour    membrane    and    containing    small    virion-like    bodies,    the    basement    membrane  of    haemocapillaries    was    hetero-geneously    thickened.    The    development    of    venulitis    was  recorded,    which    is    characterised    by    the    accumulation    of    neutrophils    in    the    vessel    wall,  pronounced    degenerative    changes    in    the    endothelium,    accompanied    by    the    
destruction    of    cytoplasmic    organelles,    vacuolisation    of    the    cytoplasm    and    its   heterogeneous   osmophilia,    the    appearance     of     heterogeneous     microvilli     on     the     lumenal    surface     of     the     endothelium,     and     heterogeneous    thickening    of    the    cytoplasmic    membrane.    Ultrastructural    changes    in    the    vascular    endothelium    in    COVID-19    indicate    the   primary    occurrence    of    acute    vasculitis    as    a    pathogenetic    dominant    in    COVID-19    pneumonia. Conclusions.     Clinical     manifestations     and     ultrastructural     pathomorphological     studies    conducted     by     us    reliably    indicate    that    the    primary    pathogenetic    basis    of    atypical    pneumonia    in    COVID-19    syndrome    is    the    occurrence     of     acute     vasculitis     with     predominant     damage     to     the     vessels     of     the     pulmonary     system.     The    
«malignant»     course     of     COVID-19     syndrome     involves     the     transformation     of     acute     vasculitis     into     systemic    vasculitis     with     subsequent     unpredictable     damage     to     a     number     of     systems     (respiratory,     cardiovascular,    hepatobiliary,    genitourinary).

Keywords SARS-CoV-2, COVID-19, vasculitis, pneumonia, pulmonary system, coronavirus infection, pathomorphology, electron microscopic changes, fatalities, forensic medicine.