Immunology of HIV infection, I: Biology of the interferons

Synergistic Inhibition of Human Immunodeficiency Virus Type 1 in vitro by Interferon Alpha and Coumermycin A1

Interferon alpha, either leukocyte derived or the recombinant form, and the DNA gyrase inhibitor coumermycin A1 both inhibited human immunodeficiency virus type 1 (HIV) replication in vitro. We have found that combinations of these two agents synergistically inhibited HIV replication in human peripheral blood leucocytes (PBL). Significant inhibition was detected when both virion-associated reverse transcriptase activity and p24 levels were used as markers of replication. Mathematical analysis of data using the procedure of Chou and Chou (1987) produced combination indices of less than 1.0 for most effect levels at several combination ratios. Synergy was also evident when the classical isobologram technique was used for data analysis. Synergistic drug interactions were observed at concentrations not associated with cytotoxicity or anti-proliferative effects, and were seen at concentrations achievable in vivo.

Interferons and interferon (IFN)-inducible protein 10 during highly active anti-retroviral therapy (HAART)-possible immunosuppressive role of IFN-alpha in HIV infection

Interferons play an important, but incompletely understood role in HIV-related disease. We investigated the effect of HAART on plasma levels of IFN-alpha, IFN-gamma, neopterin and interferon-inducible protein 10 (IP-10) in 41 HIV-infected patients during 78 weeks of therapy. At baseline HIV-infected patients had raised levels of both IP-10 and IFN-alpha compared with healthy controls (n = 19), with particularly high levels in advanced disease. HAART induced a marked decrease in levels of both IFN-alpha, neopterin and IP-10, though not to normal concentrations. In contrast, IFN-gamma levels were low throughout the study, and not different from controls. While neopterin and IP-10 remained significantly decreased compared with baseline levels throughout the study, IFN-alpha levels returned to baseline at the end of the study. Persistently high IP-10 and IFN-alpha levels were associated with immunological treatment failure and even high baseline levels of IFN-alpha appeared to predict immunological relapse. Furthermore, we found a markedly suppressive effect of exogenously added IFN-alpha on phytohaemagglutinin-stimulated lymphocyte proliferation in both patients and controls, and this suppressive effect seemed not to involve enhanced lymphocyte apoptosis. Our findings suggest a pathogenic role of IFN-alpha in HIV infection, which may be a potential target for immunomodulating therapy in combination with HAART.

Molecular mechanisms of interferon resistance mediated by viral-directed inhibition of PKR, the interferon-induced protein kinase

The interferon (IFN)-induced cellular antiviral response is the first line of defense against viral infection within an animal host. In order to establish a productive infection, eukaryotic viruses must first overcome the IFN-induced blocks imposed on viral replication. The double-stranded RNA-activated protein kinase (PKR) is a key component mediating the antiviral actions of IFN. This IFN-induced protein kinase can restrict viral replication through its ability to phosphorylate the protein synthesis initiation factor eukaryotic initiation factor-2 alpha-subunit and reduce levels of viral protein synthesis. Viruses, therefore, must block the function of PKR in order to avoid these deleterious antiviral effects associated with PKR activity. Indeed, many viruses have developed effective measures to repress PKR activity during infection. This review will focus primarily on an overview of the different molecular mechanisms employed by these viruses to meet a common goal: the inhibition of PKR function, uncompromised viral protein synthesis, and unrestricted virus replication. The past few years have seen exciting new advances in this area. Rather unexpectedly, this area of research has benefited from the use of the yeast system to study PKR. Other recent advances include studies on PKR regulation by the herpes simplex viruses and data from our laboratory on the medically important hepatitis C viruses. We speculate that IFN is ineffective as a therapeutic agent against hepatitis C virus because the virus can effectively repress PKR function. Finally, we will discuss briefly the future directions of this PKR field.

What happens inside lentivirus or influenza virus infected cells: insights into regulation of cellular and viral protein synthesis

Efficient manipulation of the regulatory mechanisms controlling host cell gene expression provides the means for productive infection by animal viruses. Upon infecting the host cell, viruses must: (i) bypass the cellular antiviral defense mechanisms to prevent the translational blocks imposed by the interferon pathway; and (ii) effectively "hijack" the host protein synthetic machinery into mass production of virion protein components. The multicomponent regulatory nature of cellular gene expression has provided the means of selecting for a diverse range of mechanisms utilized by animal viruses to ensure that replication efficiency is maintained throughout the virus life cycle. One important research component of the careful examination of gene regulation is those studies that focus on elucidating the mechanisms by which viruses control mRNA translation during host cell infection. Much of the work in our laboratory has focused on elucidating the strategies by which human immunodeficiency virus type 1 and influenza virus regulate protein synthesis during infection. Here we describe the ways in which these two distinctly different RNA viruses ensure the selective and efficient translation of their viral mRNAs in infected cells. These strategies include circumvention of the deleterious effects associated with activation of the interferon-induced protein kinase, PKR. Herein we describe our methodologies designed to elucidate the translational regulation in cells infected by these viruses. We conclude with a brief summary of new directions, utilizing these methods, taken toward understanding the translational control mechanisms imposed by these viral systems, and how our studies of virally infected cells have allowed us to identify growth-regulating components of normal, uninfected cells.

Regulation and characterization of the interferon-alpha present in patients with advanced human immunodeficiency virus type 1 disease

To examine a possible association between plasma viremia and interferon-alpha (IFN-alpha) in patients with the acquired immunodeficiency syndrome (AIDS), we performed IFN plasma immunoadsorption by apheresis (IFN-alpha apheresis) in four volunteers with AIDS who had sustained levels of endogenous plasma IFN-alpha. IFN-alpha apheresis with two plasma volume exchanges was performed daily for 5 days. Clinical signs and symptoms and hematologic, virologic, and immunologic parameters were monitored. Two subjects developed anemia from phlebotomy, and one had a catheter++-associated bacteremia. The IFN-alpha apheresis was effective only in transiently removing IFN-alpha: depletion of IFN-alpha led only to its rapid reconstitution. Cell-associated HIV-1 was unchanged, but three of four subjects had a modest decrease in culturable plasma virus burden following the procedures. The recovery of in vivo HIV-1-related IFN-alpha by apheresis allowed its biologic and biochemical characterization. The HIV-1 IFN-alpha showed characteristics on ELISA, western blot, and biologic assays similar to two subspecies of the natural protein. The natural, recombinant, and HIV-1-induced IFN-alpha s demonstrated nearly identical antiviral activities. The HIV-1 IFN-alpha eluted from the column was not acid labile. The inability of large amounts of plasma IFN-alpha found in some patients with AIDS to affect viral burden likely reflects properties of the virus or of host factors independent of IFN-alpha.

Protective effect of interferon-alpha against cell-mediated human immunodeficiency virus transmission resulting from coculture of infected lymphocytes with fetal trophoblasts

The hypothesis that the low transmission rate of HIV in utero may be due, in part, to the protective effect of IFN-producing placental trophoblasts was explored in vitro. The model consisted of H9 lymphocytes, as surrogates of maternal HIV-infected T cells, incubated for 3 h with JEG-3 trophoblasts in the presence of 10-fold dilutions of leukocyte-derived IFN-alpha (from 1000 to 0.1 IU/ml). The dose effect was monitored either directly, by measuring the levels of proviral DNA by PCR after a single round of infection, or indirectly, by coculturing infected JEG-3 with cord blood-derived MT-4 lymphocytes and determining the levels of p24 production by ELISA. Both assays revealed a dose-dependent blocking effect of IFN-alpha on cell-mediated HIV transmission. The complete inhibition of HIV infection was observed in the presence of 100 IU IFN-alpha. The efficacy of such a low dose could not be attributed to insufficient viral load because up to 10(8) infectious particles could be transmitted during cell-cell contact. An adhesion assay ruled out the possibility that IFN-alpha acts through prevention of lymphocyte-trophoblast contact. The results suggest that physiologic levels of IFN-alpha, present in the placental environment, may contribute to the protection of the fetus against HIV infection.

Identification of CD4 and major histocompatibility complex functional peptide sites and their homology with oligopeptides from human immunodeficiency virus type 1 glycoprotein gp120: role in AIDS pathogenesis

CD4 molecules interact with class II major histocompatibility complex molecules as a critical costimulatory signal in CD4+ cell immune activation. CD4 also recognizes a specific region of the human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein gp120 forming a binding site for early stages of HIV-1 infection. We designed two software packages, AUTOMAT and CRITIC, which allowed us to identify similarities between regions of HIV-1 proteins and immunoregulatory protein sequences stored in data banks. In this report we have characterized (i) a pentapeptide, SLWDQ, found in both CD4 and HIV-1 gp120, which surprisingly had remained undetected in these two well-studied molecules until now, and (ii) an HLA sequence corresponding to the putative functional site of H2 I-A. We found that a region of gp120 (residues 254-263) known to be similar to a sequence in HLA class II beta chain overlaps this functional region. We showed experimentally that these two CD4 and HLA peptide segments inhibit CD4+ cell immune activation. There is strong inhibition (50% up to 80%) of immune activation by SLWDQ-containing gp120 segments and a lesser inhibition by the gp120 HLA-homologous segment. In addition, we found that SLWDQ induced in HIV-1-infected individuals a humoral (antibody) and cellular (cytotoxic T lymphocyte) immune reaction. We propose that these HIV-1 gp120 segments, together with the known CD4-binding region, may contribute to the HIV-1-induced immunosuppression by two mechanisms affecting CD4-HLA interaction during T-cell immune activation: autoimmune reaction toward CD4 and direct interference with the CD4-HLA costimulatory signal inducing CD4+ cell anergy with, as a consequence, generation of immunosuppression.

Inhibitory effect of natural interferon alpha on human immunodeficiency virus type 1 transmission from epithelial cells to lymphocytes in vitro

The in vitro effect of human natural interferon alpha (IFN-alpha) on cell contact-mediated human immunodeficiency virus type 1 (HIV-1) transmission from epithelial cells to lymphocytes was examined. This type of infection is most likely to occur when the mucosal linings of the reproductive or digestive organs serve as latent viral reservoirs and HIV-1 invades the host through the basolateral surface of polarized epithelia upon contact with intraepithelial lymphocytes. The cell-to-cell infection model consisted of target MOLT-4 T lymphocytes exposed for various time periods to chronically HIV-1-infected intestinal monolayers (I407/YH5) in the presence of log10 dilutions of IFN (range 10(5)-10(-2) IU/ml). Concurrent measurements of resulting productive infection from MOLT-4 revealed that complete inhibition of reverse transcriptase activity was prevented by doses starting from 1 IU, whereas the cessation of p24 production occurred at 1000 IU of IFN present at inoculation. The results indicate that IFN can efficiently prevent not only cell-free but also cell-mediated HIV-1 infection--an important means of viral spread in vivo pertinent to HIV-1 transmission resulting from mucosa-lymphocyte interaction.

Cerebrospinal fluid (CSF) analyses in HIV-1 primary neurological disease

This paper will focus on CSF findings in HIV-1 Neurological Disease (ND). Why use CSF as exploration window of the HIV-CNS involvement? Traditionally, CSF analysis has been an effective diagnostic method as well as a means of monitoring treatment in several infectious and immune pathologies of the CNS. Consequently there is an abundance of mature background information [113, 145, 147] particularly in terms of detecting infectious agents, using IgG findings as immunological indexes, and utilizing CSF findings to map the evolution of ND. We will explore the papers that utilize CSF variables as dependent measures to explore the effects of HIV disease, particularly HIV ND, cited in Index Medicus and MEDLINE data base, and published in Spanish, Italian and English, between 1985 to 1991. We will restrict our review to those studies that exclude HIV cases with CNS opportunistic infections or neoplasms, and thus focus on what the CSF can tell us about the primary effects of HIV on the brain as defined above. The primary long-term goal is to find some elements of the CSF that would lead to an understanding of the etiopathogenesis of HIV ND. However, an almost equally important aim is to determine which CSF variables may be clinically predictive of HIV ND occurrence and progression. The latter variables can also be expected to provide the best measures of HIV ND treatment efficacy. This is particularly important since it is our contention that treatment of HIV ND will eventually be initiated and monitored on the basis of laboratory markers of HIV ND, most likely from the CSF. Finally, this summarized information would be useful in drafting a CSF profile in order to have a reference pattern for cases with complications. The data of this review will be broken down, when the information permits, according to clinical stage and presence or absence of clinical manifestations of ND.

Potential role of the viral protease in human immunodeficiency virus type 1 associated pathogenesis

Infection with the human immunodeficiency virus type 1 (HIV-1) results in a variety of pathological changes culminating in the acquired immune deficiency syndrome (AIDS). While most of these changes can readily be accounted for either by direct effects of HIV-1 on the immune system or by indirect effects of secondary infectious agents as a result of faulty immune surveillance, the direct cause for a number of disease states, including some neuropathies, myopathies, nephropathy, thrombocytopenia, wasting syndromes and increased incidence of cancers (primarily lymphoma) has remained an enigma. We have recently shown that the HIV-1 protease, a viral encoded enzyme necessary for virus maturation and infectivity, can cleave a variety of host cell cytoskeletal proteins in vitro. Potential substrates for the HIV-1 protease are found in all of the cell types affected in these unexplained diseases. Recent proposals suggest that elements of the cytoskeleton may play an important role in the regulation of large scale genetic regulation. We propose that some of the degenerative changes associated with infection by HIV-1 are a direct consequence of cleavage of host cell cytoskeletal proteins, which in turn may be responsible for the increased incidence of cancer in HIV-1 infected individuals as a result of the perturbation of the regulation of gene expression by cytoskeletal components.

Interferons in the persistence, pathogenesis, and treatment of HIV infection

Interferon (IFN) plays an important role in the treatment and pathogenesis of HIV disease. Recent studies show beneficial effects of IFN alpha in the treatment of HIV-associated Kaposi's Sarcoma and early HIV-infection. Moreover, cell culture studies support these beneficial effects. HIV infection of monocytes is blocked by IFN alpha administered at the time of viral challenge. The IFN alpha-treated cells show no evidence of HIV infection. Viral gene products produced in monocytes infected with HIV then treated with IFN alpha gradually decrease to baseline. Large quantities of proviral DNA are seen in the HIV-infected IFN alpha-treated cells with little evidence for viral transcription suggesting true microbiological latency. While most viral infections of cells result in IFN production, HIV is a notable exception. Indeed, HIV does not induce monocytes to produce IFN alpha and blocks its production following poly(I).poly(c) stimulation. This allows HIV yet another mechanism to evade an important host antiviral response. Paradoxically, the appearance of IFN activity in sera of HIV-infected patients is associated with disease progression, not resolution. Recent observations showing that the interaction between HIV-infected monocytes and PBMC results in the production of IFN alpha s with reduced anti-HIV activity may help explain this paradox. Thus, IFN alpha plays an important but complex role in HIV disease. The elucidation of cellular factors that regulate the antiretroviral effects of IFN alpha may lead to the development of novel therapeutic strategies for HIV infection.