A retrovirus belonging to the family of recently discovered human T-cell leukemia viruses (HTLV), but clearly distinct from each previous isolate, has been isolated from a Caucasian patient with signs and symptoms that often precede the acquired immune deficiency syndrome (AIDS). This virus is a typical type-C RNA tumor virus, buds from the cell membrane, prefers magnesium for reverse transcriptase activity, and has an internal antigen (p25) similar to HTLV p24. Antibodies from serum of this patient react with proteins from viruses of the HTLV-I subgroup, but type-specific antisera to HTLV-I do not precipitate proteins of the new isolate. The virus from this patient has been transmitted into cord blood lymphocytes, and the virus produced by these cells is similar to the original isolate. From these studies it is concluded that this virus as well as the previous HTLV isolates belong to a general family of T-lymphotropic retroviruses that are horizontally transmitted in humans and may be involved in several pathological syndromes, including AIDS.

In infants whose HIV infection is maternally acquired, the rate of disease progression varies directly with the severity of the disease in the mother at the time of delivery.

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Eight human herpesvirus 6 (HHV-6) strains were studied by Southern blot and polymerase chain reaction. DNA from infected cells was digested by a panel of restriction enzymes and hybridized with cloned BamHl fragments corresponding to about 30% of the HHV-6 strain SIE genome. In parallel, this DNA was amplified by polymerase chain reaction using pairs of primers derived from the strain SIE nucleotide sequence. Subsequently, amplification products were analyzed by hybridization, digestion with restriction endonucleases, and partial nucleotide sequencing. Overall results indicated that all strains were closely related to one another. However, concordant differences in restriction patterns allowed at least two groups to be distinguished, typified by strains SIE and HST, respectively. Differences between the two groups were found to reflect a limited number of punctual changes in nucleotide sequences. These results strengthen the idea of a unique HHV-6 species with genetic polymorphism. In addition, this study provides useful markers for the diagnosis and molecular epidemiology of HHV-6 infections.