Fayth K. Yoshimura, Ph.D. September 7, of 7 HIV - BASIC PROPERTIES

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1 1 of 7 I. Viral Origin. A. Retrovirus - animal lentiviruses. HIV - BASIC PROPERTIES 1. HIV is a member of the Retrovirus family and more specifically it is a member of the Lentivirus genus of this family. Lenti is derived from Latin and means slow, which refers to the fact that lentiviruses cause diseases which develop quite slowly, usually requiring years for the development of disease. For example, the usual time which is required for the development of AIDS after infection by HIV is roughly 10 years. 2. Table of lentiviruses. Two types of HIV, referred to as type 1 and type 2. HIV-1 was first isolated in 1983 by Luc Montagnier, who was at the Insitut Pasteur, at the time. This was just 2 years after AIDS was first described. HIV-2 was discovered about 3 years later. Although it is closely related to HIV-1, where the two viral genomes share 40% homologous, HIV-2 is not so virulent and causes a disease, which takes longer to develop and has a lower morbidity rate. HIV-2 is most prevalent in West Africa, whereas, HIV-1 is the type that is most commonly found in the rest of the world. 3. Origins and phylogenetic tree.

2 2 of 7 4. II. General Properties of HIV. A. HIV has the general characteristics of a retrovirus in that it is composed of a lipid envelope and has two identical copies of a single-stranded RNA as its genome. B. Cellular tropism. 1. CD4 T lymphocyte. HIV infects mainly T lymphocytes that express the cell surface marker CD4, which corresponds to the population known as helper T cells. 2. Monocyte/macrophage. HIV can also infect monocytes and macrophages, which are thought to be the type of cells that are initially infected by the virus. 3. Neurons - oligodendrocytes, astrocytes. Infection of these types of neurons results in the neurological disorders that are characteristic of AIDS. III. HIV Pathogenesis. A. Three main clinical symptoms of AIDS 1. CD4 T cell depletion 2. Neurological manifestations 3. Neoplasms - Kaposi s sarcoma, lymphoma B. Transmission 1. Blood 2. Sexual transmission 3. Mother to infant (intrauterine and infection at birth). Maternal-fetal transmission occurs in only about 25-30% of infants. C. Clinical course of AIDS

3 3 of 7 1. Viremia a. HIV replication is thought to occur primarily in mononuclear cells - such as, macrophages, that are present at the sites of entry. Soon after, however, replication occurs in CD4+ T lymphocytes. CD4 is the major HIV receptor. Other cofactors, corresponding to chemokine receptors (CCR5 [macrophage] and CXCR4 [T cells]), are also required. b. Viremia declines during so-called persistent phase and increases again during the development of AIDS. 2. Initial immune response corresponds to an initial increase in CTL s followed by a sustained period of anti-gp 120 Ab response. During this period viremia in PBLs and serum is kept in check although virus may be sequestered in lymph nodes. a. Immunodeficiency results from depletion of CD4+ cells. b. Some people develop symptoms resembling mild influenza or mononucleosis soon after HIV infection. c. Persistent infection. 1). Cells infected with HIV contain proviral DNA integrated into the cellular DNA. Provirus need not be expressed to be maintained by infected cell and passed on to progeny cells. 2). Only low amounts of virus produced in PBLs. However, higher amounts of virus in lymph nodes. 3). This stage of infection can last for years, asymptomatic. d. Persistent generalized lymphadenopathy syndrome (PGL). e. AIDS-related complex (ARC). Involves fever, fatigue, diarrhea, weight loss, night sweats, immunologic abnormalities. CNS damage. f. Fully-developed AIDS. Opportunistic infections, neoplasms, IV. HIV Replication.

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5 5 of 7 A. HIV has a complex genome. There are 9 major spliced messages. B. Adsorption and Entry - Receptor and co-receptor. 1. SU and V3 regions - binding to CD4 The viral protein responsible for binding to the CD4 cellular receptor is the virion glycoprotein (SU) - also referred to as gp 120 (kd). The protein is composed of both variable and constant regions of amino acids. The most important of these segments is the regions known as V3, which is the immunodominant epitope recognized by neutralizing antibodies. 2. Chemokine receptor cofactors - 2 major types cells. a. CXCR4 - α-chemokine receptor. Present on surface of CD4 T b. CCR5 - ß-chemokine receptor. Present mainly on macrophages. c. Other chemokine receptors may be involved.

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7 7 of 7 C. Viral Proteins. 1. RT Error prone polymerase, which is responsible for the high mutation rate of all retroviruses, including HIV. 2. Protease. PR is required for the cleavage of the viral polyprotein precursor to form the components of the virion, such as Gag and Matrix. 3. Regulatory Proteins. a. Tat - transcriptional transactivator. Tat is a trans-activator of viral transcription. Very little transcription of viral RNA occurs without Tat protein. Interacts with complex of proteins that binds to the promoter site of transcription. b. Rev - regulator of viral expression.

8 8 of 7 Rev regulates viral RNA transport, particularly of the unspliced RNA that is packaged into virions as genomic RNA, and that is used for the translation of the gag-pol polyprotein. The transport of singly spliced mrna to the cytoplasm is also regulated by Rev. [Singly spliced mrna is used to encode the envelope glycoprotein, an important component of infectious virus particles.] 2. Accessory Proteins. So-called because they were initially observed to be non-essential in in vitro studies. However, subsequent studies have shown that they may be important for pathogenesis in vivo. cytoplasmic. a. Nef. Negative factor (a misnomer). Predominantly 1). Downregulates CD4 and MHC class I molecules. 2). Activates cellular protein kinases. 3). Most importantly it has been shown to be crucial for the ability of SIV to induce disease in adult macaque monkeys where the infection of these monkeys with a Nef-deletion mutant of SIV was unable to cause SAIDS, and furthermore, protected the animals against subsequent infection by wild type SIV. b. Vpr. Viral Protein R. 1). Plays important role in ability of HIV to infect nondividing cells. A nuclear localization signal allows import of the preintegration complex into the nucleus of the infected cell. phase of the cell cycle. 2). Arrests cellular proliferation. Cells accumulate in G2 c. Vif - Virion Infectivity Factor 1). Virion internalization or uncoating. 2). Possibly important for virion maturation. d. Vpu. Viral Protein U. budding. 1). Downregulates CD4 expression and promotes virus V. Therapy A. Combination drugs (cocktails) B. Vaccines 1. Recombinant proteins 2. Attenuated virus 3. Other treatments - ribozymes and anti-sense

9 9 of 7 Study Questions: 1. Inhibitors of reverse transcriptase have been used in the therapeutic treatment of HIV-1 infection for the following reason: a). This protein is essential for integration of the viral DNA into the chromosomal DNA of the infected cell. b). This protein is required for the synthesis of viral DNA from the genomic RNA molecule. c). This protein plays a role in the attachment of the viral glycoprotein to the cellular receptor. d). This protein is important for efficient transcription of the proviral DNA. Answer: b). 2. Which of the following viral proteins would you pick to design a vaccine against HIV-1 that would elicit an antibody response: a). Glycoprotein b). Vpr c). Tat d). Reverse transcriptase Answer: a). This is the major virion protein that is recognized by neutralizing antibodies.

Human Immunodeficiency Virus

Human Immunodeficiency Virus Virion Genome Genes and proteins Viruses and hosts Diseases Distinctive characteristics Viruses and hosts Lentivirus from Latin lentis (slow), for slow progression of disease