Anti-neuraminidase antibody response in hamsters experimentally infected with Sendai virus

Investigations were performed to study the behaviour of neuraminidase-inhibiting (n.i.a.) and, by comparison, of neutralizing, hemagglutinin-inhibiting (h.i.a.) and anti-S and anti-V complement-fixing (c.f.a.) antibodies in hamsters inoculated intranasally with a Sendai virus strain of recent isolation. Moreover the distribution of the virus in the respiratory tract was followed. Preliminary experiences were done to assure a correct performance of the neuraminidase-inhibition test. First of all the optimal pH and then the influence of the normal hamster serum on the enzyme activity were evaluated. The n.i.a. as well as h.i.a. and anti-S and anti-V c.f.a. were demonstrable from day 6th after infection, neutralizing antibody from 8th day. The n.i.a. reached the peak of 24 days, that is later than the other types of antibodies, and started to decline after 1 month, together with the drop of the h.i.a and c.f.a. On the contrary the neutralizing antibody persisted at high titres till the end of the observation period (75 days). Detectable antibody response was coincidental with a marked drop in the titers of virus recovered from the respiratory tract. Because of the association of both hemagglutinating and neuraminidase activities with the same Sendai glycoprotein, it is stressed the possibility that hemagglutination-inhibition and neutraminidase-inibition tests titrate the same antibody.