The synthesis and processing of the human immunodeficiency virus 1 (HIV-1) envelope precursor glycoprotein gpl60 was studied in an infected CD4' lymphocytic cell line. Surprisingly, only a small percentage (5-15%) of gpl60 is cleaved to produce the mature gpl20 component. Intracellular sorting results in the transfer of most uncleaved gpl60 to lysosomes, where it is degraded, while gpl20 is transported to the cell surface and subsequently secreted. Cleavage of gpl6O to generate gpl20 occurs intracellularly and can be inhibited by NH4Cl. Taken together, these results indicate that intracellular cleavage of gpl60 determines the intracellular transport and survival of the envelope glycoproteins necessary to produce infectious virus.Human immunodeficiency virus 1 (HIV-1) is a human retrovirus and the primary etiological agent associated with the acquired immunodeficiency syndrome (AIDS). Like other retroviruses, the HIV-1 genome encodes envelope glycoproteins, which project from the membrane surface of mature particles. The external glycoproteins of several viruses are synthesized as precursor molecules, which are ultimately processed to mature proteins that mediate functions required for infection (1). These include the gp70/pl5E envelope gene products of the murine retroviruses, the HA1/HA2 hemagglutinin proteins of the influenza virus, and the F1/F2 fusion proteins of Sendai virus (1, 2). The same is true for HIV-1, in which the gpl60 glycoprotein precursor is cleaved to form the external gpl20 and gp4l membrane-associated envelope components (3, 4). The cleavage of gpl60 is essential for HIV-1 infectivity (5). Functional studies indicate that gpl20 is responsible for the adsorption of virions to the CD4 receptor (6, 7), while gp4l mediates the fusion of viral and cellular membranes (8,9). Expression of HIV-1 envelope proteins on the surface of infected cells can also lead to cell-to-cell fusion, resulting in the formation of syncytia (10).While information continues to accumulate pertaining to the functional characterization of the envelope glycoproteins, the intracellular synthesis and processing of these proteins is not well understood. In this study we have quantitatively analyzed the fate of newly synthesized gpl60 during productive HIV-1 infection of CD4+ cells. Pulsechase analyses indicate that only a small fraction of the precursor gpl60 is processed into the mature gpl20 component. The uncleaved gpl60 is efficiently transported to and degraded within lysosomes, while a greater proportion of the gpl20 remains stable and is eventually secreted from the cell.MATERIALS AND METHODS Cell Cultures. A3.01, a human lymphocytic leukemia cell line (11), was maintained in RPMI 1640 medium (GIBCO) supplemented with 10% (vol/vol) heat-inactivated fetal calf serum (RPMI/FCS). Peripheral blood lymphocytes were grown in RPMI/FCS medium containing 0.25 ,ug of phytohemagglutinin per ml for 3 days prior to infection. The cells were then transferred to and maintained in RPMI/FCS medium containing human interleukin...

Human immunodeficiency virus (HIV) frequently causes neurological dysfunction and is abundantly expressed in the central nervous system (CNS) of acquired immunodeficiency syndrome (AIDS) patients with HIV encephalitis or myelopathy. The virus is found mostly in cells of the monocyte-macrophage lineage within the CNS, but the possibility of infection of other glial cells has been raised. Therefore, the effects of different HIV-1 and HIV-2 strains were studied in primary cultures of adult human brain containing microglial cells, the resident CNS macrophages, and astrocytes. These cultures could be productively infected with macrophage-adapted HIV-1 isolates but not with T lymphocyte-adapted HIV-1 isolates or two HIV-2 isolates. As determined with a triple-label procedure, primary astrocytes did not express HIV gag antigens and remained normal throughout the 3-week course of infection. In contrast, virus replicated in neighboring microglial cells, often leading to their cell fusion and death. The death of microglial cells, which normally serve immune functions in the CNS, may be a key factor in the pathogenesis of AIDS encephalitis or myelopathy.

Treatment of purified bovine coronavirus (Mebus strain) with pronase destroyed the integrity of virion surface glycoproteins gp140, gp120, gp100, reduced the amount of gp26 and destroyed the hemagglutinating activity of the virus. Bromelain, on the other hand, destroyed the integrity of gp120, gp100 and gp26 but failed to remove gp140 and failed to destroy viral hemagglutinating activity. These experiments suggest that gp140 is the virion hemagglutinin. Immunoblotting studies using monospecific antiserum demonstrate that gp140 is a disulfide-linked dimeric structure reducible to monomers of 65 kDa.

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To understand the potential role of placental tissue in the pathogenesis of neonatal AIDS, the distribution of human immunodeficiency virus type 1 (HIV-1) receptor and the infectability of placental tissue by HIV-1 were studied. Both the mRNA and the protein for the HIV receptor (CD4) were present in fetal-derived placenta. By immunofluorescent microscopy, a number of different cell types appeared to be CD4+; positive cells were observed in the lining and stroma of the chorionic villi. Some of these CD4+ cells dual-labeled with the trophoblastic marker placental lactogen. In addition, CD4+ cells were observed within the lining of placental blood vessels. Organ cultures of first-trimester and term placentas were infectable by HIV as monitored by reverse transcriptase activity of culture supernatants and by immunofluorescent labeling of HIV antigens. One potential route of congenital HIV transmission may be direct placental infection by HIV as early as the first trimester, with subsequent transplacental spread of the virus.