Syncytium

Syncytium (from Greek syn — together and kytos — cell) is a large multinucleated cell structure not divided by cellular membranes.

In infectology, the formation of a syncytium is a specific cytopathic (destructive) effect caused by certain viruses upon infection of human tissues.

Etiology and pathophysiology

Some RNA- and DNA-containing viruses (primarily the respiratory syncytial virus, coronaviruses, herpes simplex viruses) have specific fused proteins (F-proteins) on their outer shell.

The process of the viral infection and syncytium formation occurs as follows:

1. viral penetration — when a virus penetrates into a human cell, the infected cell releases new viruses into neighboring healthy cells;
2. action of molecular glue — the infected cell may continue to produce viruses or may fuse with other cells using a fusion protein (F-protein);
3. cell fusion — as a result, dozens of individual cells merge into a single structure with multiple nuclei (syncytium).

Clinical significance

The formation of syncytia leads to rapid and massive death of healthy tissue.

The clinical and diagnostic significance of the phenomenon is as follows:

• necrosis of affected tissue — a cell that has turned into a syncytium loses its functions and soon dies (for example, in infections caused by the respiratory syncytial virus, the ciliated epithelium of the respiratory tract merges into multinucleated layers, which then die off and shed in whole pieces into the lumen of the bronchi);
• Virus Detection — in laboratory diagnostics, the phenomenon is used for identifying pathogens: when examining smears microscopically (e.g., Tzanck test for herpes), a laboratory physician visually searches for characteristic giant multinucleated cells, which directly confirms the infection.