OBJECTIVE

To evaluate the representation and localization of FAP-positive activated stromal cells depending on the severity of fibrotic changes in tissues of patients with a confirmed diagnosis of COVID-19.

MATERIAL AND METHODS

20 autopsy observations of patients who died from COVID-19 were studied. Immunohistochemical studies were performed using antibodies to CD90, FAP and aSMA and a dual imaging system. The severity of fibrosis in lung tissue was assessed according to the R.Hubner scale (2008).

RESULTS

FAP-positive cells are detected in the lungs, kidneys, liver and myocardium, while only in the lungs FAP expression is associated with fibrotic tissue areas. FAP expression of varying intensity was observed in capillaries, alveolar and bronchial epithelium, as well as in fibrotic nodules in the lungs, where it partially colocalizes with the key myofibroblast marker aSMA. CD90-positive stromal cells were also predominantly found in fibrotic foci.

CONCLUSION

The results obtained allow us to clarify the localization of activated stromal precursors in human tissues during injury and suggest an important role of FAP in the formation of fibrotic foci and the progression of fibrotic changes in tissues, primarily the lungs, which makes it a promising pharmaceutical target for the treatment of diseases associated with the development of fibrosis.