The influence of protease inhibitors of the organism, especially bovine aprotinin, on the production of virulent hog cholera virus in tissue cultures.

The influence of biological protease inhibitors, especially aprotinin, on the production of virulent hog cholera virus in cell cultures. Production of number and size of fluorescent plaques after infection PK 15 cells with HC virus depended on properties of fetal calf sera added to the medium. By affinity chromatography on bovine alpha-chymotrypsin bound to CM-cellulose inhibitory proteins against chymotrypsin-like proteases could be eliminated from inhibiting sera. The fraction free from inhibitors did not inhibit plaque formation of HC virus in contrast to the fraction containing the eluted inhibitor(s). The inhibitory properties of fetal calf sera could be measured by a plaque inhibition test. By this test no inhibitory component could be demonstrated in 30 individual serum samples from pigs which on subsequent infection with HC virus exhibited virus growth to high titres. The serum from one pig, however, was found to inhibit HC virus plaque formation in PK 15 cells. When infected, this animal reacted with an unexpected low virus replication and mild disease symptoms. The production of virulent HC virus could likewise be inhibited by addition to the medium of the bovine protease inhibitor aprotinin; the degree of inhibition being dependent on the concentration. Virulent virus was produced again after elimination of this inhibitor from the medium. A weak inhibitory effect on plaque formation was also achieved by addition of the protease inhibitor chymostatin (3 mg/5 mg) and human alpha 1x plasma inhibitor to the medium of infected cells. The inhibitory effect appears to be very specific.