Attachment of influenza C virus to human erythrocytes.

Binding experiments with radioactively labelled influenza C virions were carried out to investigate the interaction of the virus with human erythrocytes. The erythrocytes from any of 35 different individuals were found to contain influenza C virus-binding sites though their number was variable among the individuals and was much less than that on mouse, rat and chicken erythrocytes. Attachment of influenza C virus to human erythrocytes was inhibited completely by prior treatment of the virus with anti-HE monoclonal antibody having a strong haemagglutination inhibition activity. Pretreatment of erythrocytes with neuraminidase or the neuraminate-O-acetylesterase of influenza C virus resulted in a marked reduction in the level of virus binding. Thus it appears that human erythrocytes have a low level of O-acetylated sialic acid-containing glycoconjugates that can interact specifically with the HE glycoprotein of influenza C virus. Proteolytic digestion of erythrocytes with ficin, bromelain or V-8 protease inhibited virus binding almost completely, suggesting that the erythrocyte receptor for influenza C virus is a glycoprotein. In contrast to these enzymes, trypsin treatment of erythrocytes reduced virus binding by only about 50%, and alpha-chymotrypsin treatment did not inhibit at all. It was also found that treatment of erythrocytes with monoclonal antibody to the M or N blood group antigen greatly inhibited virus binding to the cells. These results, taken together, suggest that most influenza C virus receptors on human erythrocytes, if not all, reside on glycophorin A which is known to possess the M or N blood group activity.

The use of the anti-Acholeplasma activities of Streptomyces culture filtrates for the screening of new antibiotics.

A screening method for new antimicrobial agents from streptomyces culture filtrates was developed. Three different types of test organisms were used for determining the antimicrobial activities of the culture filtrates: they were (a) an antibacterial activity test against Staphylococcus aureus, (b) an antimycoplasmal activity test against Acholeplasma laidlawii, and (c) a cytotoxicity test against HeLa-S3 cells. The active filtrates showing antimicrobial spectra (anticellogram) which did not match those of known antimicrobial agents were used for further purification to obtain new antimicrobial agents. Of these screening methods, antimycoplasmal activity against Acholeplasma laidawii was the most sensitive for discriminating new compounds contained in the filtrates of known antibiotics.