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Pneumotropism of Sendai virus in relation to protease-mediated activation in mouse lungs
Abstract:
The pneumotropism of Sendai virus in mice was studied in relation to the activation and replication of the virus in the lung. Inactive Sendai virus grown in LLC-MK(2) cells, which possessed an uncleaved precursor glycoprotein, F, and was noninfectious to tissue culture cells, neither grew nor caused pathological changes in the lung of mice. When trypsin treatment was made which cleaved F into F(1) and F(2) subunits, the virus became activated so that it could initiate replication in the bronchial epithelium of the lung. In this case, the progeny virus was produced in the activated form and multiple-cycle replication occurred successively. A parallel relationship was found between the degree of the viral replication and that of clinical signs of the respiratory disease, body weight loss, and histopathological changes in the lung. A protease mutant, TR-2, which was able to be activated only by chymotrypsin but not by trypsin, could also initiate replication in the bronchial epithelium, when activated by chymotrypsin before inoculation into mice. The progeny virus, however, remained inactive, and the replication was limited to a single cycle, which resulted in the limited lung lesion. The overall results suggest that some activating mechanism for the progeny virus of wild-type Sendai virus exists in the lung of mice and the principle (activator) responsible for this phenomenon has a character similar to trypsin. The possible location of the activator is discussed.
Insights
Sendai virus requires activation by proteases like trypsin for lung replication in mice. The mouse lung likely contains a trypsin-like activator essential for sustained Sendai virus spread and disease.
Area of Science:
- Virology
- Immunology
- Pathology
Background:
- Sendai virus pneumotropism is crucial for respiratory disease.
- Viral activation depends on the cleavage of the F glycoprotein precursor.
Purpose of the Study:
- To investigate Sendai virus activation and replication in the mouse lung.
- To identify the mechanism of viral spread within the respiratory tract.
Main Methods:
- In vitro activation of Sendai virus using trypsin and chymotrypsin.
- Inoculation of mice with activated and non-activated virus.
- Assessment of viral replication, clinical signs, and lung pathology.
Main Results:
- Inactive Sendai virus did not replicate or cause pathology in mice.
- Trypsin activation enabled viral replication and disease progression.
- A protease mutant (TR-2) showed limited replication, indicating the progeny virus remained inactive.
- A trypsin-like activator in the mouse lung facilitates sustained viral replication.
Conclusions:
- Sendai virus activation is essential for pneumotropism and pathogenesis in mice.
- The mouse lung possesses an endogenous activator, similar to trypsin, for progeny virus activation.
- This activator plays a key role in the multi-cycle replication and spread of Sendai virus.