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By using in situ hybridization methodology, we have directly examined primary lymph node and peripheral blood from patients with acquired immunodefIciency syndrome (AIDS) and AIDS-related complex for the presence of human T-lymphotropic virus type M (HTLV-l) viral RNA. Mononuclear cell preparations were hybridized with a 35s labeled HTLV-II-specific RNA probe and exposed to autoradiographic emulsion for 2 days. HTLV-III-infected cells expressing viral RNA were detected in '86% (6/7) oflymph node and 50% (7/14) of peripheral blood samples studied. However, in all patient samples eained, labeled cells were observed at very low frequency (<0.01% of total mononuclear cells). The HTLV-II-infected cells exhibited morphological characteristics consistent with that of lymphocytes and expressed viral RNA at relatively low abundance (20-300 copies per cell).These results demonstrate that HTLV-lI expression in lymph node and peripheral blood is very low in vivo. Furthermore, the lymph node hyperplasia observed in HTLV-Il-associated lymphadenopathy is not directly due to proliferation of HTLVrn-infected lymphocytes.The acquired immunodeficiency syndrome (AIDS) presents a severe unexplained immune deficiency that involves reduction in the number ofhelper T lymphocytes (OKT4) (1-3). The disease is usually accompanied by multiple opportunistic infections and/or malignancies, the latter predominantly of the Kaposi sarcoma type (4). AIDS-related complex (ARC) encompasses milder forms and sometimes prodromal states of the disease, and it is characterized by other clinical manifestations, most frequently unexplained chronic lymphadenopathy or leukopenia involving helper T lymphocytes (1-4). Recent serologic and viral isolation studies have shown that the development of AIDS or ARC is due to infection with the human retrovirus, human T-cell lymphotropic virus type III (HTLV-III) (5-8). HTLV-III, a cytopathic virus, is included in the HTLV family because of multiple biological and structural properties in common with HTLV types I and II (reviewed in ref. 9), including: (i) tropism for lymphocytes; (ii) particular tropism for OKT4 helper T lymphocytes; (iii) magnesium-dependent reverse transcriptase of high molecular weight; (iv) induction of giant multinucleated cells in culture; (v) impairment of T-cell functions; (vi) immunological crossreactivity of some virally encoded proteins; (vii) double-spliced 3' terminal mRNA; (viii) relatively small major core protein (p24/p25); (ix) unique juxtaposition of p24/p25 to the NH2-terminal gag protein-i.e., absence of the gag gene-encoded phosphoprotein in this position; and (x) trans-acting transcriptional activity resulting from a specific protein encoded by a viral gene.By using cloned HTLV-III probes (10, 11), analysis of fresh tissue from AIDS and ARC patients was carried out for detection of viral sequences. Southern blot experiments detected HTLV-III viral DNA at low levels in fresh lymphoid tissue from a number, albeit a minority, ofpatients with AIDS or ARC (12). At the s...

A variant of human T-lymphotropic virus type III (HTLV-III) is described that replicates but does not kill normal human T cells in vitro. This variant, designated X10-1, was derived from the genome of a cytopathic HTLV-III clone (pHXB2D) by excision of a 200-base pair segment in the 3' region of the virus, spanning the env and 3'-orf genes. Comparable variants with 55 to 109 base pairs deleted exclusively in 3'-orf produced, in contrast, virus that was extremely cytopathic. On the basis of these findings it is concluded that the 3'-orf gene is not required for cytopathogenicity or replication of HTLV-III. In addition, the results suggest that virus replication and cytotoxicity are not intrinsically coupled. Furthermore, since clone X10-1 retains the ability to trans-activate genes linked to the viral long terminal repeats, trans-activation per se is not responsible for T-cell killing by HTLV-III. These results also raise the possibility that the carboxyl terminus of the envelope gene of HTLV-III has a direct role in T-cell killing by this virus.

A majority of pediatric patients and rare adult patients with the acquired immunodeficiency syndrome (AIDS) develop a chronic respiratory disorder referred to as "lymphocytic interstitial pneumonitis" (LIP). Efforts to identify an infectious agent responsible for this process so far have failed. In this study, frozen sections of lungs from patients with AIDS and pulmonary disease were tested by in situ molecular hybridization for the presence of cells infected with human T-cell lymphotropic virus type III (HTLV-III) and expressing viral RNA. In the case of an infant with LIP, a relatively high frequency (0.1%) of cells in the lung were found to be positive for HTLV-III RNA. This number is the lower limit of total cells infected since the in situ hybridization technique as applied in this study depends on expression of HTLV-III genes, and previous evidence indicates that a proportion of cells infected with HTLV-III may not express viral RNA. Moreover, this degree of infection of the lung is likely limited to LIP, since in ten patients with AIDS and pulmonary diseases other than LIP, only 0% to 0.002% of cells in lung were positive for viral RNA expression. Thus, HTLV-III may play a direct causal role in the development of LIP in infected patients, implicating its involvement in yet another of the diverse clinical diseases associated with this virus.

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