Human CD4 was expressed on a range of mammalian cell lines. CD4+ non-primate cells, derived from rat, hamster, mink, cat, and rabbit, bind recombinant gp120 of human immunodeficiency virus type 1 (HIV-1) but are resistant to HIV-1 infection. CD4 expression on various human, rhesus, and African green monkey cell lines confers differential susceptibilities for HIV-1, HIV-2, and simian immunodeficiency (SIV) strains. For example, CD4+ TE671 rhabdomyosarcoma cells are sensitive to HIV-1 and HIV-2 but resistant to SIV, whereas CD4+ U87 glioma cells are resistant to HIV-1 infection but sensitive to HIV-2 and SIV. HIV-1 infection was not dependent on human major histocompatibility class I expression. Studies of cell fusion and of infection by vesicular stomatitis virus pseudotypes bearing HIV-1 and HIV-2 envelopes showed that the differential cell tropisms of HIV-1, HIV-2, and SIV are determined at the cell surface.

Sulfated polysaccharides have been shown to inhibit human immunodeficiency virus (HIV) infection in vitro. Dextrin sulfate, fucoidan, and dextran sulfate fail to neutralize virions directly, but interact with target cells to inhibit virus entry. Ionic interactions of sulfated polyanions with oppositely charged cell surface components, including CD4, have been assumed to be the inhibitory mechanism. It is shown that the sulfated polysaccharides inhibit infection of both CD4+ and CD4- cell lines by HIV and also that they inhibit HTLV-1 and, to a lesser extent, the simian retrovirus, MPMV, which use receptors other than CD4. One binding site for radiolabeled fucoidan on the surface of human T cells is an 18 kD protein, but its significance is not yet clear.

Previous studies have demonstrated the absence of viral replication of Vif ؊ mutants in stimulated primary blood mononuclear cells (PBMC). Human immunodeficiency virus type 1 strain NDK Vif ؊ mutants were propagated on the semipermissive CEM cell line, and the viral stock obtained was compared with the wild-type virus during a single cycle in PBMC. The Vif ؊ virus was able to enter PBMC with the same efficiency as the wild type, as demonstrated by quantification of the strong-stop cDNA, and retrotranscription was observed for both viruses within 4 h postinfection. Using a PCR assay with an Alu-long terminal repeat pair of primers, we detected integration for both the wild-type and Vif ؊ viruses. We then used qualitative and quantitative reverse transcription-mediated PCR techniques to study the steady-state level of intracellular and extracellular viral RNAs. All mRNA species were detected in PBMC infected with the wild-type virus or with the Vif ؊ virus 36 h postinfection. Furthermore, quantification of viral RNA released from infected cells demonstrated similar levels of virus produced after a unique cycle of replication. However, the Vif ؊ virus obtained after one replication cycle in PBMC was unable to initiate retrotranscription in permissive target cells. These data strongly suggest that the failure to infect target cells is due to a defect in the formation of the viral particle in PBMC.

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A germline T-cell receptor variable region (V beta) gene segment (V beta 14) has been mapped 10 kilobases to the 3' side of the constant region (C beta 2) gene. The V beta 14 gene segment is in an inverted transcriptional polarity relative to the diversity-region (D beta) and joining-region (J beta) gene segments and the C beta genes. Analyses of a T-cell clone (J 6.19), which has productively rearranged the V beta 14 gene segment, indicate that the productive V beta-D beta-J beta rearrangement and its reciprocal flank recombination product are linked and located at either border of a chromosomal inversion. These data demonstrate for the first time a linkage between mammalian V and C genes and verify that a functional T-cell receptor V beta gene can be constructed through a chromosomal inversion.

The Vif protein of human immunodeficiency virus type 1 is required for productive replication in peripheral blood lymphocytes. Previous reports suggest that vif-deleted viruses are limited in replication because of a defect in the late steps of the virus life cycle. One of the remaining questions is to determine whether the functional role of Vif involves a specific interaction with virus core proteins. In this study, we demonstrate a direct interaction between Vif and the Pr55 Gag precursor in vitro as well as in infected cells. No interaction is observed between Vif and the mature capsid protein. The Pr55 Gag-Vif interaction is detected (i) in the glutathione S-transferase system, with in vitro-translated proteins demonstrating a critical role of the NC p7 domain of the Gag precursor; (ii) with proteins expressed in infected cells; and (iii) by coimmunoprecipitation experiments. Deletion of the C-terminal 22 amino acids of Vif abolishes its interaction with the Pr55 Gag precursor. Furthermore, point mutations in the C-terminal domain of Vif which have been previously shown to abolish virus infectivity and binding to cell membranes dramatically decrease the Gag-Vif interaction. These results suggest that the interaction between Vif and the Pr55 Gag precursor is a critical determinant of Vif function.

The infectivity of primary HIV-1 X4 isolates and of TCLA viruses is increased upon viral incorporation of HLA Cw4 molecules. This effect is associated with changes in viral envelope proteins conformation including an enhanced expression of the V3 loop of gp120, and of epitopes that are exposed upon CD4 binding. The gp120 conformational changes are consistent with the formation of a multimolecular complex between HLA class I and gp120/160. HLA Cw4 incorporation is also associated to a lower susceptibility to antibody neutralization. These findings have important implications for understanding the immune response to cryptic and conformational epitopes of the viral envelope.

Seventeen monoclonal anti-Thy-1 antibodies (mAb) derived from LOU/M rats immunized with mouse T cell clones were used to study the role of Thy-1 in antigen-independent T cell activation. These mAb identified Thy-1.2 or monomorphic determinants and immunoprecipitated a molecule of 25-28 kDa from detergent-solubilized, 125I-labeled T cell surface proteins. Competitive cross-inhibition binding assays demonstrated that these reagents defined 3 epitope groups including either Thy-1.2 (group A) or Thy-1 monomorphic (groups B and C) determinants. Experiments using high titered culture supernatants revealed that all 6 IgG mAb defining the epitope group C, and one IgG2c mAb directed at a determinant in group A were capable of stimulating the terpolymer-L-glutamic acid60-L-alanine33-Ltyrosine10 (GAT) plus I-Ad-reactive BALB/c T cell hybridoma T14-117.9 to produce interleukin 2 (IL2) in the absence of accessory cells. Cross-linking of cell-bound rat mAb by a BALB/c anti-rat kappa chain mAb, or the presence of B cell lymphomas in the culture resulted in an increase of the Thy-1-mediated IL2 responses of this hybridoma. Some mAb from group B required antibody doses exceeding 80 micrograms/ml in order to activate T cells, while others remained nonstimulatory at any dose tested. Striking synergy in mAb-mediated T cell activation was observed when nonmitogenic doses of mAb group groups A and C were mixed in the same culture. Analysis of a panel of GAT plus I-Ad-specific T cell hybridomas revealed that these cells markedly differed in the magnitude of their IL2 responses induced by a given amount of stimulating anti-Thy-1 mAb. Such reagents also stimulated normal thymocytes to express IL2 receptor on their surface. These studies show that the epitopic specificity and the amount of anti-Thy-1 mAb, and the susceptibility of the T cell examined represent important parameters for the triggering of the Thy-1 pathway of T cell activation.