Further studies of HIV morphology by negative staining.

Thin-section studies of HIV-1- and HIV-2-infected cells were used to establish peak virus productivity and distribution of virus on and around infected cells. Maximum virus yields occurred 7 days after passage; cells at that stage were used as a source of virus for negative staining. Various methods of separating virus and cells were assessed: results showed that gentle homogenization in a Tenbroek-type homogenizer yielded considerably more virus than other techniques. Virus obtained in this way mainly appeared in the form of large clumps. Because of the large numbers of virus particles obtained it was possible to visualize what is probably the immature form of the virus. The inner component of this particle is spherical and, as is discussed, is a transient form proceeding to the now well established, mature, cone-shaped virus core.