Inhibition of plating of human T cell leukemia virus type I and syncytium-inducing types of human immunodeficiency virus type 1 by polycations

Quantification of infectious HIV-1 plasma viral load using a boosted in vitro infection protocol

Methods currently used for HIV-1 viral load measurements are very sensitive, but cannot distinguish between infectious and noninfectious particles. Here we describe the development of a novel, sensitive, and highly reproducible method that allows rapid isolation and quantification of infectious particles from patient plasma. By immobilizing HIV-1 particles in human plasma to platelets using polybrene, we observed a 10- to 1000-fold increase in infectivity over infection protocols using free virus particles. Using this method, we evaluated infectivity in plasma from 52 patients at various disease stages. At plasma viral loads of 1000-10000 HIV-1 RNA copies/ml 18%, at 10,000-50,000 copies/ml 73%, at 50,000-100,000 copies/ml 90%, and above 100,000 copies 96% of cultures were positive. We found that infectious titers among patients vary distinctively but are characteristic for a patient over extended time periods. Furthermore, we demonstrate that by evaluating infectious titers in conjunction with total HIV RNA loads, subtle effects of treatment intervention on viremia levels can be detected. The immobilization procedure does not interfere with viral entry and does not restore the infectivity of neutralized virus. Therefore, this assay system can be utilized to investigate the influence of substances that specifically affect virion infectivity such as neutralizing antibodies, soluble CD4, or protease inhibitors. Measuring viral infectivity may thereby function as an additional, useful marker in monitoring disease progression and evaluating efficacy of antivirals in vivo.

Similar regulation of cell surface human T-cell leukemia virus type 1 (HTLV-1) surface binding proteins in cells highly and poorly transduced by HTLV-1-pseudotyped virions

Little is known about the requirements for human T-cell leukemia virus type 1 (HTLV-1) entry, including the identity of the cellular receptor(s). Previous studies have shown that although the HTLV receptor(s) are widely expressed on cell lines of various cell types from different species, cell lines differ dramatically in their susceptibility to HTLV-Env-mediated fusion. Human cells (293, HeLa, and primary CD4(+) T cells) showed higher levels of binding at saturation than rodent (NIH 3T3 and NRK) cells to an HTLV-1 SU immunoadhesin. A direct comparison of the binding of the HTLV-1 surface glycoprotein (SU) immunoadhesin and transduction by HTLV-1 pseudotyped virus revealed parallels between the level of binding and the titer for various cell lines. When cells were treated with phorbol myristate acetate (PMA), which down-modulates a number of cell surface molecules, the level of SU binding was markedly reduced. However, PMA treatment only slightly reduced the titer of murine leukemia virus(HTLV-1) on both highly susceptible and poorly susceptible cells. Treatment of target cells with trypsin greatly reduced binding, indicating that the majority of HTLV SU binding is to proteins. Polycations, which enhance the infectivity of several other retroviruses, inhibited HTLV-1 Env-mediated binding and entry on both human and rodent cells. These results suggest that factors other than the number of primary binding receptors are responsible for the differences in the titers of HTLV-1 pseudotypes between highly susceptible cells and poorly susceptible cells.

Characterization of the anti-HIV effects of native lactoferrin and other milk proteins and protein-derived peptides

In a search for natural proteins with anti-HIV activity, we screened a large set of purified proteins from bovine milk and peptide fragments thereof. Because several charged proteins and peptides are known to inhibit the process of virus entry, we selected proteins with an unusual charge composition or hydrophobicity profile. In contrast with some chemically modified (strongly negative) milk proteins, unmodified alpha(s2)-, beta- and kappa-casein, as well as several negatively and positively charged fragments thereof, did not show significant inhibition of virus replication. In fact, HIV-1 replication was elevated in the presence of beta-casein or amphiphilic fragments thereof. Bovine lactoferrin (bLF), a milk protein of 80 kDa, showed considerable inhibitory activity against HIV-1 with an IC50 of 0.4 microM. Modest inhibition was obtained with lactoferricin, a highly positively charged loop domain of bLF, indicating that other domains within the native bLF protein may also be required for inhibition. bLF blocked HIV-1 variants that use either the CXCR4 or the CCR5 coreceptor. In order to obtain further insight into the mechanism of action of this antiviral protein, we selected a bLF-resistant HIV-1 variant. The bLF-resistance phenotype is mediated by the viral envelope protein, which contains two interesting mutations that have previously been associated with an altered virus-host interaction and a modified receptor-coreceptor interaction. These results demonstrate that bLF targets the HIV-1 entry process.

Envelope-dependent, cyclophilin-independent effects of glycosaminoglycans on human immunodeficiency virus type 1 attachment and infection

Cell surface glycosaminoglycans (GAGs), in particular heparan sulfate (HS), have been proposed to mediate the attachment of human immunodeficiency virus type 1 (HIV-1) to target cells prior to virus entry, and both the viral gp120 envelope protein and virion-associated cyclophilin A (CypA) have been shown to directly interact with HS and its analogues. To determine the role of GAGs in HIV attachment and infection, we generated HIV-susceptible derivatives of CHO cell lines that either express high levels of GAGs (CHO-K1) or lack GAGs (pgsA745). Using a panel of HIV-1 envelopes, we found that cell surface GAG-mediated effects on virion attachment and infection vary in an envelope strain-dependent but coreceptor-independent manner. In fact, cell surface GAG-mediated enhancement of infection is confined to isolates that contain a highly positively charged V3-loop sequence, while infection by most strains is apparently inhibited by the presence of GAGs. Moreover, the enhancing and inhibitory effects of polycations and polyanions on HIV-1 infection are largely dependent on the presence of cell surface GAGs. These observations are consistent with a model in which GAGs influence in vitro HIV-1 infection primarily by modifying the charge characteristics of the target cell surface. Finally, the effects of GAGs on HIV-1 infection are observed to an equivalent extent whether CypA is present in or absent from virions. Overall, these data exclude a major role for GAGs in mediating the attachment of many HIV-1 strains to target cells via interactions with virion-associated gp120 or CypA.

Infection of mesangial cells with HIV and SIV: identification of GPR1 as a coreceptor

BACKGROUND

Mesangial cells are an important component of the glomerulus. Dysfunction of mesangial cells is thought to be involved in the development of human immunodeficiency virus type 1 (HIV-1)-associated nephropathy (HIVAN). HIVAN is a structural renal failure frequently observed in patients with acquired immune deficiency syndrome. However, the susceptibility of mesangial cells to HIV-1 is disputable. More than ten G protein-coupled receptors, including chemokine receptors, have been shown to act as HIV-1 coreceptors that determine the susceptibilities of cells to HIV-1 strains with specific cell tropisms.

METHODS

We examined the susceptibility of mesangial cells to various HIV-1, HIV type 2 (HIV-2) and simian immunodeficiency virus (SIV) strains. Expression of CD4 and HIV/SIV coreceptors was examined by Western blotting and polymerase chain reaction.

RESULTS

Mesangial cells were found to be susceptible to HIV-1 variant and mutants that infect brain-derived cells, but highly resistant to T-tropic (X4), M-tropic (R5) or dual-tropic (X4R5) HIV-1 strains. In addition, mesangial cells were also susceptible to HIV-2 and SIV strains that infect the brain-derived cells. Among HIV/SIV coreceptors we tested, the expression of GPR1 mRNA was detected in mesangial cells. Expression of CD4 mRNA and protein was also detected in them. Mesangial cells and GPR1-transduced CD4-positive cells showed similar susceptibilities to the HIV-1 variant and mutants and HIV-2 and SIV strains.

CONCLUSIONS

CD4 and GPR1 mRNAs were detected in mesangial cells. Mesangial cells were susceptible to HIV/SIV strains that use GPR1 as a coreceptor. Our findings suggest that an orphan G protein-coupled receptor, GPR1, is a coreceptor expressed in mesangial cells. It remains to be investigated whether the interaction of mesangial cells with specific HIV-1 strains through GPR1 plays a role in the development of HIVAN.

A putative G protein-coupled receptor, RDC1, is a novel coreceptor for human and simian immunodeficiency viruses

More than 10 G protein-coupled receptors (GPCRs) have been shown to act as coreceptors for infection of human immunodeficiency virus type 1 (HIV-1), HIV-2, and simian immunodeficiency virus (SIV). We have isolated HIV-1 variants infectious to primary brain-derived CD4-positive cells (BT-3 and BT-20/N) and U87/CD4 glioma cells that are resistant to T-cell line-tropic (T-tropic), macrophage-tropic (M-tropic), and T- and M-tropic (dualtropic) (X4, R5, and R5X4) HIV-1 strains. These primary brain-derived cells were also highly susceptible to HIV-2(ROD), HIV-2(SBL6669), and SIV(mndGB-1). A factor or coreceptor that determines the susceptibility of these brain-derived cells to these HIV and SIV strains has not been fully identified. To identify this coreceptor, we examined amino acid sequences of all known HIV and SIV coreceptors and noticed that tyrosine residues are well conserved in their extracellular amino-terminal domains. By this criterion, we selected 18 GPCRs as candidates of coreceptors for HIV and SIV strains infectious to these brain-derived cells. mRNA expression of an orphan GPCR, RDC1, was detected in the brain-derived cells, the C8166 T-cell line, and peripheral blood lymphocytes, all of which are susceptible to HIV-1 variants, but not in macrophages, which are resistant to them. When a CD4-expressing cell line, NP-2/CD4, which shows strict resistance to infection not only with HIV-1 but also with HIV-2 or SIV, was transduced with the RDC1 gene, the cells became highly susceptible to HIV-2 and SIV(mnd) strains but to neither M- nor T-tropic HIV-1 strains. The cells also acquired a low susceptibility to the HIV-1 variants. These findings indicate that RDC1 is a novel coreceptor for several HIV-1, HIV-2, and SIV strains which infect brain-derived cells.

Unique morphological alterations of the HTLV-I transformed C8166 cells by infection with HIV-1

C8166 cells express T lymphocyte markers, a monocyte-specific esterase, taxpolypeptide of HTLV-I. In spite of this transactivator, their HIV-1 yield is low. Their culture conditions were modified, and infected cells were immobilized on a poly-L-lysine sheet under semisolid overlays to study their phenotypic alterations and HIV-1 production by microscopy and electron microscopy. Another lymphoid cultures (MT-4, CEM, CEM-ss, AdCEM) similarly treated were infected with either HIV-1/RF or IIIB. Specificity of HIV-1 was compared to the effects of vesicular stomatitis virus (VSV). Unlike other cultures, HIV-1/RF infected C8166 cells in Eagle s MEM exhibited surface projections resembling hairy leukemia cells, which was followed by balloon degeneration and apoptosis. Immobilized HIV-1 infected cultures formed flat syncytia with several interdigitating dendritic projections. Syncytia shrunk with condensed nuclear material and axon-like filaments characteristic for infected macrophages. VSV induced enlargement and necrotic lysis of all cell types. Early postinfection with HIV-1, electron microscopy revealed irreversible membrane fusion above cell nuclei, and transient fusion between filaments. Transient presence of coated vesicles containing intact HIV-1 particles, Birbeck granule-like structures of Langerhans cells, fibrillar-lamellar structures resembling hairy leukemia or Sézary cells were detected. Late postinfection, high proportion of HIV-1 bud from polarized cytoplasm was empty particle, while that bud and entrapped in cytoplasmic vacuoles contained two or multiple cores in a fused envelope. The effect of early gene products of HIV-1 on HTLV-I and C8166 cells might elicit their latent potentials for monocyte or interdigitating dendritic cells, while in the later phase HTLV-I products might alter HIV-1 virion assembly.

Inhibition of HIV-1 infection by zinc group metal compounds

Thirty-seven metal compounds were examined for inhibitory activities against infection with human immunodeficiency virus type 1 (HIV-1). Zinc group metal compounds, namely, zinc acetate, zinc chloride, zinc nitrate, cadmium acetate and mercury chloride, showed anti-HIV-1 activities. Cadmium and mercury compounds at 1-10 microg/ml and zinc compounds at 100 microg/ml strongly inhibited HIV-1 infection, although the cadmium, mercury and zinc compounds had severe cytotoxities at 100, 100 and 1000 microg/ml, respectively. They inhibited transcription of HIV-1 RNA and HIV-1 production at concentrations at which they did not affect the growth of HIV-1-producing cells. They had little effect on syncytium formation resulting from cocultivation of uninfected with HIV-1-producing cells. Nor did they affect HIV-1 DNA synthesis following HIV-1 infection. The metal compounds may owe their anti-HIV-1 effects to inhibition of HIV-1 DNA to RNA transcription, rather than inhibition of the adsorption, penetration or reverse transcription step of HIV-1 infection.

Changes in and discrepancies between cell tropisms and coreceptor uses of human immunodeficiency virus type 1 induced by single point mutations at the V3 tip of the env protein

We examined the effect of amino acid substitutions of the GPGR (glycine-proline-glycine-arginine) tip sequence at the V3 domain of the Env protein of human immunodeficiency virus type 1 (HIV-1) on its cell tropism and coreceptor use. We changed the GPGR sequence of a T-cell line (T)- and macrophage (M)-tropic (R5-R3-X4) HIV-1 strain, GUN-1wt, to GA(alanine)GR (the resulting mutant was designated GUN-1/A), GL(leucine)GR (GUN-1/L), GP(proline)GR (GUN-1/P), GR(arginine)GR (GUN-1/R), GS(serine)GR (GUN-1/S), or GT(threonine)GR (GUN-1/T). GUN-1/A, GUN-1/S, and GUN-1/T mutants infected brain-derived cells such as a CD4-transduced glioma cell line, U87/CD4, and a brain-derived primary cell strain, BT-20/N, as well as T-cell lines in a CD4-dependent manner, although the plating of these mutants onto macrophages was inhibited. GUN-1/L, GUN-1/P, and GUN-1/R mutants showed both T- and M-tropism, but did not plate onto the brain-derived cells. A CCR3, CCR5, CCR8, or CXCR4 gene was introduced into a CD4-positive glioma cell line, NP-2/CD4, which demonstrated complete resistance to various HIV-1 strains. Not only HIV-1 strains, which were infectious to macrophages, such as GUN-1wt, GUN-1v, GUN-1/L, and GUN-1/P, but also an HIV-1 strain, GUN-1v, which was hardly infectious to macrophages, grew well in NP-2/CD4 cells expressing CCR3 or CCR5. However, the M-tropic GUN-1/R mutant could not efficiently use CCR5 nor CCR3. No point mutants, except GUN-1/L, grew well in NP-2/CD4 cells expressing CCR8. These findings indicate that the cell tropism of HIV-1 to macrophages and brain-derived cells and their use of the coreceptors were markedly, though not always concomitantly, affected by the tip sequence of the V3 domain.

Isolation and characterization of a monoclonal antibody that inhibits HIV-1 infection

To identify a cell surface molecule other than CD4 involved in infection of cultured cells with human immunodeficiency virus type 1 (HIV-1), mice were immunized with the CD4-negative Raji human B-cell line in order to isolate a monoclonal antibody (mAb). We isolated mAb 33A, which inhibited the infection of CD4-positive T cells, B cells, human peripheral blood lymphocytes (PBL), and brain-derived cells with HIV-1. Formation of viral DNA was also blocked when CD4-positive Raji cells were treated with 33A after adsorption of HIV-1, but not before its adsorption. mAb 33A had little effect on syncytium formation induced by cocultivation with HIV-1-producing cells. Flow cytometry revealed that 33A reacted with HTLV-I-positive T-cell lines, Burkitt's lymphoma cell lines, phytohemagglutinin (PHA) -stimulated PBL, brain-derived fibroblast-like cells, and some adherent cell lines, but hardly at all with immature T-cell lines. Immunoblotting experiments showed that 33A recognized an antigen with an apparent molecular mass of 32 kDa, but did not recognize chemokine receptors such as CXCR4, CCR5, or CCR3. The distribution characteristic of the antigen recognized by 33A on various cells and its molecular weight suggest that mAb 33A recognizes a new cellular antigen that is necessary for HIV-1 entry.

Identification of membrane antigens important for adsorption of human T-cell leukaemia virus type I

We isolated three monoclonal antibodies (mAbs), H3e, H11b and H16h, which were capable of inhibiting syncytium formation induced in a human T-cell line MOLT-4 or a human glioma line U251 MG by coculture with human T-cell leukaemia virus type I (HTLV-I)-positive human T-cell lines. The mAbs partially inhibited the plating of pseudotypes of vesicular stomatitis virus (VSV) bearing envelope antigens of HTLV-I. Formation of proviral DNA was also inhibited when indicator cells were treated with the mAbs before adsorption of HTLV-I, but not after its adsorption. They did not inhibit syncytium formation induced by human immunodeficiency virus type 1. Flow cytometry revealed that H16h hardly reacted with various HTLV-I-positive T cells, while H3e and H11b reacted with HTLV-I-positive human cells as well as HTLV-I-negative human cells. H11b and H16h immunoprecipitated the membrane antigen with a molecular weight of 20 and 110-130 kDa, respectively. Western blot analysis showed that H3e, H11b and H16h bound to the protein of 20, 20 and 110-130 kDa, respectively. Thus, these findings suggest that the 20- and 110-130-kDa cell surface proteins may play a role at the early stage of HTLV-I infection.