HIV Primer (2021) PDF

PRIMER DOCUMENT ON HIV-DR. VISHY VENKETARAMAN, PROFESSOR, COMP INTRODUCTION TO VIRUS AND HUMAN IMMUNODEFICIENCY: Slide #1-10 OBJECTIVES: Describe virus the characteristics, transmission, risk factors, epidemiology, clinical presentation,...

PRIMER DOCUMENT ON HIV-DR. VISHY VENKETARAMAN, PROFESSOR, COMP INTRODUCTION TO VIRUS AND HUMAN IMMUNODEFICIENCY: Slide #1-10 OBJECTIVES: Describe virus the characteristics, transmission, risk factors, epidemiology, clinical presentation, pathogenesis, and prevention for HIV. INTRODUCTION TO VIRUS:.N. Characteristics Viruses 1 Size Smaller (20-400 nm) 2 Cell Wall No cell wall. Protein coat present instead. 3 Ribosomes Absent Number of 4 No cells cells Living/Non- 5 Between living and non-living things. Living 6 DNA and RNA DNA or RNA enclosed inside a coat of protein. 7 Infection Systemic 8 Reproduce Need a living cell to reproduce Invades a host cell and takes over the cell causing it to make copies o 9 Reproduction host cell releasing new viruses. Duration of 10 Most viral illnesses last 2 to 10 days. illness 11 Fever A viral infection may or may not cause a fever. Cellular 12 Lack cellular machinery Machinery Under 13 Visible only under Electron Microscope. Microscope Viruses are not beneficial. However, a particular virus may be able to 14 Benefits be useful in genetic engineering. 15 Treatment Virus does not respond to antibiotics. 1  PRIMER DOCUMENT ON HIV-DR. VISHY VENKETARAMAN, PROFESSOR, COMP HIV: Human immunodeficiency virus or HIV is responsible for causing AIDS or acquired immunodeficiency syndrome. Ever since, HIV was first discovered in 1981 more than 40 million people have died because of AIDS. Currently, 36.9 million people are infected with HIV, of which two-thirds of whom live in sub-Saharan Africa where people have limited access to health care. AIDS is the fourth leading cause of death worldwide. HIV preferentially infects and kills CD4+ T lymphocytes and macrophages, resulting in the loss of immunity and hence susceptibility to opportunistic pathogens. A normal healthy individual has CD4 T cell counts between 500-1500/mm3. Whereas individuals with AIDS have CD4 counts below 200.mm3 and this results in compromised levels of cytokines such as IL-2, IFN-γ and IL-17. IL-2 produced by Th1 CD4 T cells maintains the viability of all T cells (CD4 and CD8). IFN-γ produced by Th1 CD4 T cells enhances the effector functions of innate and adaptive immune cells. IL-17 produced by Th17 CD4 T cells provides mucosal immunity and protects against both intracellular and extracellular infections. 2  PRIMER DOCUMENT ON HIV-DR. VISHY VENKETARAMAN, PROFESSOR, COMP Therefore, decreased levels of IL-2, IFN-γ and IL-17, cause individuals with AIDS highly susceptible to opportunistic infections. HIV also infects other cells such as macrophages, DCs and monocytes. Transmission of HIV occurs primarily by sexual contact and by transfer of infected blood. Both HIV-1 and HIV-2 cause AIDS, but HIV-1 is found worldwide, whereas HIV-2 is found primarily in West Africa. SLIDE#11-12: HIV genome and proteins: HIV belongs to the retrovirus group and contains two identical copies of RNA as genetic material or genome and reverse transcriptase enzyme that converts RNA to cDNA. HIV also belongs to the lentivirus subgroup of retroviruses, which cause "slow" infections with long incubation periods. HIV has a bar-shaped (type D) core surrounded by an envelope containing virus-specific glycoproteins (gp120 and gp41). The genome of HIV consists of three genes such as gag, pol, and env, that encode the structural proteins and six regulatory genes. The gag gene encodes the internal "core" proteins, the most important of which is p24, an antigen used in serologic tests. The pol gene encodes several proteins, including the virion "reverse transcriptase," which synthesizes DNA by using the genome RNA as a template, an integrase that integrates 3  PRIMER DOCUMENT ON HIV-DR. VISHY VENKETARAMAN, PROFESSOR, COMP the viral DNA into the cellular DNA, and a protease that cleaves the various viral precursor proteins. The env gene encodes gp160, a precursor glycoprotein that is cleaved to form the two envelope (surface) glycoproteins, gp120 and gp41. SLIDE#13-15: Replication of HIV: The initial step involved in the entry of HIV into the host cell is the binding of the gp120 envelope protein present on the viral envelope to the CD4 protein on the cell surface of either T cells or macrophages. The virion gp120 protein then interacts with a second protein (a chemokine receptor CCR5 or CXCR4) on the cell surface of macrophages or CD4 T cells. Next, the virion gp41 protein mediates fusion of the viral envelope with the host cell membrane, and the virion enters the cell. Chemokine receptors, such as CXCR4 and CCR5 proteins, are required for the entry of HIV into CD4-positive cells. Those HIV strains that specifically bind to the CXCR4 are called T-cell-tropic strains of HIV, whereas the macrophage-tropic strains bind to CCR5. After uncoating, the virion RNA-dependent 4  PRIMER DOCUMENT ON HIV-DR. VISHY VENKETARAMAN, PROFESSOR, COMP DNA polymerase transcribes the genome RNA into double-stranded DNA, which integrates into the host cell DNA. Viral DNA can integrate at different sites in the host cell DNA, and multiple copies of viral DNA can integrate. Viral mRNA is transcribed from the proviral DNA by host cell RNA polymerase and translated into several large polyproteins. The Pol polyprotein is cleaved to form the reverse transcriptase, integrase, and protease. The immature virion containing the precursor polyproteins forms in the cytoplasm, and cleavage by the viral protease occurs as the immature virion buds from the cell membrane. It is this cleavage process that results in the mature, infectious virion. SLIDE#16-17: HIV and immunopathogenesis: CD4 T cell depletion: HIV infects helper T cells (CD4-positive cells) and kills them, resulting in suppression of cell-mediated immunity. This predisposes the host to various opportunistic infections. The initial infection of the genital tract occurs in dendritic cells that line the mucosa (Langerhans' cells), after which the local CD4-positive helper T cells become infected. HIV is first found in the blood 4 to 11 days after infection. CD8 T cells play an important role in controlling HIV infection. SLIDE#18-22: HIV and the Th1 to Th2 Cytokine shift HIV causes a shift in CD4 T cell responses from Th1 to Th2. T cells contribute to adaptive immune responses against infections. T cells are classified into two major groups CD4 and CD8 T cells. CD4 T cells recognize processed antigen peptide on the cell surface of antigen presenting cells (APC) associated with MHC class II. Whereas CD8 T cells recognize processed antigen peptide on the cell surface of APC associated with MHC class I. CD4 T cells are called helper T cells due to the fact that they produce cytokines that either enhance the effector functions of macrophages, neutrophils and CD8 T cells or induce B cells to produce different classes of antibodies. 5  PRIMER DOCUMENT ON HIV-DR. VISHY VENKETARAMAN, PROFESSOR, COMP CD8 T cells play an important role in protection against viral infections and cancer. CD8 T cells are also called cytotoxic T cells since they produce antimicrobial proteins such as perforin and granulysin that kill the host cells and the intracellular virus. CD8 T cells also produce granzymes that can induce apoptosis of host cells leading to the death of the intracellular viral or bacterial pathogens. CD4 T cell subsets: CD4 T cells are divided into different subsets such as Th1, Th2 and Th17, based on the cytokines produced by each subset. Polarizing cytokines produced by the APCs induce differentiation of CD4 T cells to various subsets. Interleukin-12 (IL-12) produced by activated APCs causes CD4 T cells to differentiate into the Th1 subset of cells. These Th1 cells then secrete a characteristic Th1 profile of cytokines consisting of interleukin-2 (IL-2) and interferon- gamma (IFN-γ). IL-2 induces proliferation of both CD4 and CD8 T cells thereby amplifying the T cell responses. IFN-γ induces further IL-12 production in activated APCs, amplifying the Th1 response, and suppressing any Th2 response. IFN-γ plays an important role in enhancing the effector functions of macrophages and neutrophils to control intracellular infections. IFN-γ also plays a pivotal role in activation of cytotoxic TC cells which destroy virus-infected cells and cancer cells. In contrast, IL-10 (and IL-4) produced by activated APCs causes CD4 T cells to differentiate into the Th2 subset of cells. Th2 cells then secrete cytokines such as IL-4 (B cell growth factor) and IL-5 (B cell differentiation factor). These cytokines induce B cells to produce different classes of antibodies. IL-23 produced by activated APCs causes CD4 T cells to differentiate into the Th17 subset of cells. Th17 cells produce IL-17, which attracts neutrophils to the site of bacterial infection. 6  PRIMER DOCUMENT ON HIV-DR. VISHY VENKETARAMAN, PROFESSOR, COMP Under normal conditions, the immune system utilizes a Th1 subset response to control intracellular infections. In individuals infected with HIV, the normal Th1 response to infection is shifted to a Th2 response. Measurement of the serum cytokine levels of HIV infected patients has revealed an increase in Th2 cytokines as well as a decrease in Th1 cytokines. Assays have shown elevated serum IL-4 levels in HIV seropositive individuals. IL-4 in the presence of proliferating T0 cells leads to their differentiation into the Th2 subset. Th2 cells promote B- cell proliferation, class switching, and eosinophil activation. This Th2 response is not appropriate for control of intracellular pathogens, and furthermore, antibodies are not very effective in neutralizing HIV and as result the virus persist and spread in CD4+ T-cells leading to loss of immunity and susceptibility to opportunistic infections. SLIDE#23-27: The main immune response to HIV infection consists of cytotoxic CD8-positive lymphocytes: As I just said before, CD8 T cells play an important role in protection against HIV infection. CD8 T cells are also referred to as cytotoxic T cells since they produce antimicrobial proteins such as perforin and granulysin that kill the host cells and the intracellular virus. CD8 T cells also produce granzymes that can induce apoptosis of host cells leading to the death of the intracellular viral or bacterial pathogens. CD8 T cells respond by controlling HIV infection for many years. However, as mutant strains of HIV emerge, especially when the mutant env gene encoding gp120, arise, cytotoxic T cells lose their ability to control the mutant strain. It is the ultimate failure of these cytotoxic T cells that results in the clinical picture of AIDS. 7  PRIMER DOCUMENT ON HIV-DR. VISHY VENKETARAMAN, PROFESSOR, COMP Cytotoxic T cells also lose their effectiveness because so many Th1 CD4 helper T cells have died; thus, the supply of lymphokines, such as IL-2 and IFN-γ, required to activate and keep the cytotoxic T cells viable is no longer sufficient. SLIDE#28-32: Clinical findings: Stages of HIV infection: Acute stage: The clinical picture of HIV infection can be divided into three stages: an early, acute stage; a middle, latent stage; and a late, immunodeficiency stage. In the acute stage, which usually begins 2 to 4 weeks after infection, an infectious mononucleosis-like picture of fever, lethargy, sore throat, and generalized lymphadenopathy occurs. A maculopapular rash on the trunk, arms, and legs (but sparing the palms and soles) is also seen. Leukopenia occurs, but the number of CD4 cells is usually normal. A high-level viremia typically occurs, and the infection is readily transmissible during this acute stage. This acute stage typically resolves spontaneously in about 2 weeks. Resolution of the acute stage is usually accompanied by a lower level of viremia and a rise in the number of CD8-positive (cytotoxic) T cells directed against HIV. Antibodies to HIV typically appear during this time (10 to 14 days) after infection, and most patients will have seroconverted by 3 to 4 weeks after infection. Note that the inability to detect antibodies prior to that time can result in” false-negative” serologic tests (i.e., the person is infected, but 8  PRIMER DOCUMENT ON HIV-DR. VISHY VENKETARAMAN, PROFESSOR, COMP antibodies are not detectable at the time of the test). This has important implications because HIV can be transmitted to others during this period. For example, if the antibody test is negative but HIV infection is still suspected, then a polymerase chain reaction (PCR)–based assay for viral RNA in the plasma should be done. Of those who become seropositive during the acute infection, approximately 87% are symptomatic (i.e., about 13% experience an asymptomatic initial infection). chemoprophylaxis against opportunistic organisms. Latent stage: In the middle stage of HIV infection, a long latent period, measured in years, usually ensues. In untreated patients, the latent period typically lasts for 7 to 11 years. The patient is asymptomatic during this period. Although the patient is asymptomatic and viremia is low or absent in circulation, a large amount of HIV is being produced by lymph node cells but remains sequestered within the lymph nodes. This indicates that during this period of clinical latency, the virus itself does not enter a latent state. A syndrome called AIDS-related complex (ARC) can occur during the latent period. The most frequent manifestations are persistent fevers, fatigue, weight loss, and lymphadenopathy. ARC often progresses to AIDS. Late stage: The late stage of HIV infection is AIDS, manifested by a decline in the number of CD4 cells to below 200/μL and an increase in the frequency and severity of opportunistic infections. 9  PRIMER DOCUMENT ON HIV-DR. VISHY VENKETARAMAN, PROFESSOR, COMP SLIDE#33-35: AIDS and opportunistic infections: The most characteristic manifestation of AIDS is pneumonia caused by Pneumocystis jiroveci. However, many other opportunistic infections occur with some frequency. These include viral infections such as disseminated herpes simplex, herpes zoster, and cytomegalovirus infections and progressive multifocal leukoencephalopathy; fungal infections such as thrush (caused by Candida albicans), cryptococcal meningitis, and disseminated histoplasmosis; protozoal infections such as toxoplasmosis and cryptosporidiosis; and disseminated bacterial infections such as those caused by Mycobacterium avium- intracellulare and Mycobacterium tuberculosis. Many AIDS patients have severe neurologic problems (e.g., dementia and neuropathy), which can be caused by either HIV infection of the brain or by many of these opportunistic organisms. 10  PRIMER DOCUMENT ON HIV-DR. VISHY VENKETARAMAN, PROFESSOR, COMP SLIDE#36-40: The point of care for the diagnosis of early infections is the HIV antigen/antibody “Combo” test that detects the presence of p24 antigen as well as antibodies to both HIV-1 and HIV-2. This combination test is useful for the diagnosis of early infections because p24 antigen is typically detectable earlier in infection than antibody. Other laboratory tests that are important in the management of an HIV-infected person include CD4 cell counts, viral load assays, and tests for drug resistance of the strain of HIV infecting the patient. CD4 T cells can be quantified using flow cytometry. CD4 T cell counts below 200 cell/mm3, the individual is considered to have AIDS. Prevention and treatment: When HIV progress to stage 3, where CD4+ T cell counts fall below 200 cell/mm3, the individual is considered to have AIDS. If an HIV infected individual is diagnosed with an opportunistic infection, regardless of CD4+ T cell count level, this individual is also considered to have AIDS. Currently, the most effective treatment for HIV is antiretroviral therapy (ART). This therapy is a lifelong treatment but is not a cure for HIV or AIDS. In 2013, the WHO recommended treatment initiation start when CD4+ T cell counts fall below 500 cells/mm3. However, with new findings, in a 2016 report from the WHO, it is now recommended that ART starts immediately, regardless of CD4 count. As of 2015, 37 million individuals worldwide have HIV or AIDS. Within this population, 17 million people are on ART. Combined with therapy, a key factor to the treatment of HIV and AIDS patients is to prevent opportunistic infections. STUDY GUIDE HIV Retrovirus, Lentivirus Gag, Pol, Env gp120, gp41 p24, integrase, reverse transcriptase, and protease gp120, gp41, CXCR4, CCR5 and their role in viral infection AIDS 11  PRIMER DOCUMENT ON HIV-DR. VISHY VENKETARAMAN, PROFESSOR, COMP Replication of HIV in CD4 T cells and macrophages Role of CD4 and CD8 T cells in mediating host immune responses against HIV HIV induced shift in CD4 T cell responses from Th1 to Th2 HIV and depletion of TH17 subset of CD4 T cells HIV and depletion of TH1 subset of CD4 T cells Ineffective CD8 T cell responses against HIV infection Stages in HIV infection (acute, latent and AIDS) AIDS and opportunistic infections (Pneumocystis jirovecii, Pneumocystis carinii, Herpes simplex, Herpes zoster, cytomegalovirus. Candida albicans, cryptococcus, histoplasmosis; toxoplasmosis, M. avium and M. tuberculosis) Laboratory diagnosis of HIV infection 12