Retroviruses: new viral infections in man

Abstract

Human retroviruses, or RNA viruses, including the 2 HIV agents associated with AIDS, and the 2 HTLV agents causing leukemia, are described from the viewpoint of history, detection, serology, transformation mechanism, disease pathophysiology, genetic function, associated disease, and related viruses. Both HTLV and HIV infect the human T-lymphocytes, also known as CD4 or helper cells. Both can now be grown in culture, and their genomes are well characterized. HTLV, an acronym for human T-lymphotropic leukemia virus, causes the fulminating adult T-cell leukemia-lymphoma (ATLL), 1st described in 1977. It is prevalent in population clusters, notably in the Caribbean and in southwestern Japan, and is spread by sexual, blood and perinatal routes, as is HIV. It is thought to promote transformation of target cells by release of growth promoting, soluble factor, perhaps a product of the viral "tat" gene. Besides leukemia, HTLV-1 causes a myelopathy sometimes called tropical spastic paraparesis. HIV, formerly known as HTLV-III, causes depletion of the T-cells, and also infects the brain and nervous system. IT has also been isolated from semen, cervical secretions, saliva, monocytes, milk, endothelial cells, tears and cornea. HIV has 5 more genes than HTLV, which regulate transcription, mRNA processing and virus maturation. Parts of the HIV genome are highly heterogeneous, and mutate rapidly, notable sections of the envelope protein. Thus, HIV has 2 main subtypes, but others are known and probably exist. Approaches toward developing AIDS therapeutic agents as of 1987 are outlined: an effective drug should cross the blood-brain barrier. Several anti-viral drugs that block the enzyme reverse transcriptase area being investigated. Possible mechanisms for growth of Kaposi's sarcoma, activation of herpes type viruses, and animal viruses related to HTLV and HIV are discussed.