Mechanisms of neutralization of influenza virus by IgM.

IgM which neutralized influenza virus infectivity by over 99% prevented the attachment of only half the virus population to BHK cells at 37 degrees C. However, the half of the population that attached to cells was not internalized. Loss of infectivity brought about by IgM is thus totally different from that caused by neutralizing IgG which does not inhibit attachment or penetration.