Properties of the Rat Submaxillary Gland Virus Haemagglutinin and Antihaemagglutinin and Their Incidence in Apparently Healthy Gnotobiotic and Conventional Rats

The properties of the rat submaxillary gland (RSMG) virus haemagglutinin and its serum antihaemagglutinin, and their incidence and relative titres in gnotobiotic and conventional Sprague-Dawley rats of various ages were investigated. The haemagglutinin was stable at -55° for as long as years and retained its activity after 2 hr at 60°. Various carbohydrases and cobra venom had no effect upon its titre; however, 2 × crystallized trypsin and pronase reduced the titre substantially. The haemagglutinin was not recovered from the submaxillary glands of rats less than 8 weeks of age, though 3-, 5-, and 6-week-old animals had low serum antihaemagglutinin titres. A general correlation was observed between the haemagglutinin and antihaemagglutinin titres of the animals; higher serum antihaemagglutinin titres occurred in those rats with higher haemagglutination titres. No significant difference was usually seen between the haemagglutination titres of gnotobiotic and conventional rats of the same age. The antihaemagglutinin titres of some conventional rats, however, tended to be two- to fourfold greater than those of gnotobiotic animals of comparable age with identical haemagglutination titres. Sera which were heated at 56° for 30 min. absorbed with kaolin, incubated with trypsin, potassium or sodium periodate, or receptor-destroying enzyme showed no reduction in their antihaemagglutinin titres. Sucrose density-gradient centrifugation studies indicated that the antihaemagglutinin was associated with the 7 S fraction; however, some sera showed antihaemagglutinin activity in the 19 S fraction. The haemagglutinin of rat submaxillary gland virus was not inhibited by antisera prepared in mice against reovirus 3, Kilham’s rat virus, Toolan’s H-1 virus or Crawford’s minute virus of mice.