Hypothesis on the molecular basis of nononcogenic retroviral diseases.

Oncogenic and nononcogenic retroviruses have similar structures and replicate by reverse transcription of their viral RNAs. The nononcogenic retroviruses are distinguished from the oncogenic retroviruses by virtue of the chronic inflammatory or degenerative disease they cause. These diseases include visna-maedi of sheep, caprine arthritis and encephalitis, equine infectious anemia, and chronic spongiform polioencephalomyelopathy of mice. The basis for the particular disease caused by the nononcogenic retroviruses seems to be the selective infection of specific end-stage cells. A common factor in these slowly progressing diseases is lifelong persistence of virus with viral spread either in the face of host immunity-antigenic drift or by modulation of the host immune response. The molecular basis for antigenic drift in visna virus and its biologic significance are discussed.