An African green monkey lacking peripheral CD4 lymphocytes that retains helper T cell activity and coexists with SIVagm

Natural infection with simian immunodeficiency virus (SIV) is known to occu r in the African green monkey (AGM). The actual onset of the disease has no t been recognized in SIVagm infected AGM, and the precise reason for such a pathogenicity in the AGM remains unclear. We reported previously that AGM p eripheral CD4 lymphocytes underwent a peculiar differentiation from CD4(+) to CD4(-) cells after in vitro activation, and we inferred that the AGM doe s not fall into a fatal immunodeficient state because of the generation of CD4(-) helper T cells in vivo. To evaluate this possibility, we examined th e relationship between CD4 expression and helper T cell activity in the nat urally infected AGM. We identified a healthy monkey almost lacking CD4 T ce lls in the periphery. This ACM showed no signs and symptoms' of immunodefic iency and retained a helper T cell activity in antibody production comparab le to those of CD4(+) AGMs. In addition, SIVagm could be isolated from CD8( +) lymphocytes in the CD4(-) AGM. These observations suggest that a unique host-virus adaptation has developed in the AGM, and may be helpful in expla ining the fundamental reason for the apathogenicity occurring in this monke y.