alpha-chymotrypsin and Paramyxoviridae-Infections

A protease-activation mutant of Sendai virus, TCs, was isolated from a trypsin-resistant mutant, TR-5. TCs was activated in vitro by both trypsin and chymotrypsin. TCs was, however, less sensitive to trypsin and chymotrypsin than were the wild-type virus and TR-5, respectively. F protein of TCs had a single amino acid substitution at residue 114 from glutamine to arginine, resulting in the appearance of the new cleavage site for trypsin and the shift of the cleavage site for chymotrypsin. Activation of TCs in the lungs of mice occurred less efficiently than that of the wild type, and TCs caused a less severe pneumopathogenicity than did the wild-type virus, which supports our previous view that the in vitro trypsin sensitivity of Sendai virus can be a good indication of pneumopathogenicity in mice.

Topics: Amino Acid Sequence; Animals; Base Sequence; Chymotrypsin; Lung; Lung Diseases; Mice; Molecular Sequence Data; Mutation; Parainfluenza Virus 1, Human; Paramyxoviridae Infections; Trypsin; Viral Fusion Proteins; Virus Replication

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.

Topics: Animals; Bronchi; Chymotrypsin; Lung; Male; Mice; Mice, Inbred ICR; Parainfluenza Virus 1, Human; Paramyxoviridae Infections; Peptide Hydrolases; Trypsin; Virus Activation; Virus Replication

Treatment of peripheral blood lymphocytes from normal donors with small amounts of purified Sendai virions results in enhanced cellular cytotoxicity in vitro to uninfected tissue culture target cells (virus-dependent cellular cytotoxicity (VDCC)), without any obvious correlation to the natural cytotoxicity (NK) displayed by the lymphocytes in the absence of virus. Removal from the virions of the two surface components present in the viral envelope, the HN glycoprotein (gp 71), carrying haemagglutinating and neuraminidase activity, and the F glycoprotein (gp 49), carrying fusion activity, by treatment with pronase abrogated their capacity to induce VDCC. Similar results were obtained when virions lacking the HN glycoprotein after treatment with chymotrypsin were added to the lymphocytes. In contrast, treatment of the virus particles with trypsin, which removed the F glycoprotein, did not affect their capacity to induce VDCC. When the solubilized and separated peplomers were used for lymphocyte treatment, either alone or in combination, the purified HN glycoprotein had full capacity to induce VDCC, whereas the F glycoprotein was inactive. These results suggest that the HM peplomer is solely or primarily responsible for the cytolytic activity arising in non-sensitized lymphocytes when confronted with certain viruses.

Topics: Adult; Chymotrypsin; Cytotoxicity, Immunologic; Dose-Response Relationship, Immunologic; Humans; Kinetics; Lymphocytes; Paramyxoviridae Infections; Pronase; Trypsin; Viral Envelope Proteins; Viral Proteins