AIDS and STDs - Assignment Example

WEEK 2 HOME WORK HOMEWORK ASSIGNMENT WEEK 2 What are the 2 main arms of the immune system? What are the main functions of these 2 arms? There are two major arms of the human immune system: (1) innate immunity and (2) acquired immunity. Innate immunity refers to immune elements which are non-specific. They are generally able to distinguish foreign tissues and organisms, but are unable to recognize a particular invader. Similarly, they will respond to such an organism in the same manner, despite repeated exposures to it - they do not adapt and improve their effectiveness against previously encountered antigens. The acquired immune system is responsible for the destruction of foreign particles once they have entered the body. Acquired immunity is a useful evolutionary adaptation because it improves the efficacy of the innate immune response by focusing the response to the site of invasion/infection as well as providing additional effector mechanisms that are unique to lymphocytes. 2. What are the 2 major cell types in blood and what are there functions? What quantity of each of these cell types do healthy adults normally have in their blood? The two major cell types in blood are white blood cells and red blood cells. Red blood cells are the most common type of blood cells which functions as the principal means to deliver oxygen from the lungs to body tissues through blood. Adult humans have roughly 2–3 × 1013 red blood cells at any given time (women have about 4 million to 5 million erythrocytes per cubic millimeter (microliter) of blood and men about 5 million to 6 million. On the other hand, white blood cells are components of the blood. They are manufactured in the bone marrow and are instrumental in depending the body against infectious diseases and foreign substances. White blood cells are part of the immune system. In a normal adult, There are normally between 4x109 and 11x109 white blood cells in a litre of healthy adult blood — about 7,000 to 25,000 white blood cells per drop. 3. Describe the major cells of the immune system and their main functions. B-cells circulate throughout the body with antibody molecules on their surfaces. When they pick up the signal of a particular antigen, they multiply and transform into plasma cells, which are essentially minifactories with one purpose: to churn out the precise antibodies that hook onto the antigens of the interloper. T-cells, on the other hand, migrate to the thymus. There, with the aid of various thymic hormones, immature T-cells grow, learn to recognize and attack antigens, and develop a range of specialized activities. The thymus is the master gland of cell-mediated immunity, a veritable training school for different classes of T-cells. There are three types of T-cells: T-helper cells which orchestrate the actions of other immune cells; killer T-cells which liquidate invading microbes, viruses or cancer cells; and suppressor cells which maintains properly balanced immune responses. 4. What does MHC stand for? What is it? Why is it important in the context of disease-causing agents? MHC stand for major histocompatibility complex which is a group of genes that code for certain proteins that are found in the surface of cells and help the immune system recognize foreign substances. MHC is an essential component of the immune response as they allow the T-cells of the immune system to recognized body cells which are invaded by infectious substances. The MHC molecules do this by presenting fragments of proteins belonging to the invader on the cells surface. The T cell recognizes the foreign peptide attached to the MHC molecule and binds to it, stimulating the T cell to either destroy or cure the infected cell. In uninfected healthy cells the MHC molecule presents peptides from its own cell, to which T cells do not normally react. 5. Compare and contrast viruses and bacteria. Both virus and bacteria both has the capacity to bring diseases. Also, both organisms contain DNA and enzymes. Amidst these similarities, a virus is smaller than bacteria which also has a more complex structure. Virus has a spiky outer skin while bacteria is protected by its rigid cell wall. Bacteria has lots of DNA blueprint facilitating rapid reproduction. In contrast, virus cannot reproduce easily because of their lack of DNA blueprint. 6. What is the “central dogma” once commonly held in molecular biology? What discovery threw that theory off? The central dogma of molecular biology was first enunciated by Francis Crick in 1958. The central dogma of molecular biology deals with the detailed residue-by-residue transfer of sequential information. It states that such information cannot be transferred from protein to either protein or nucleic acid. In other words, “once information gets into protein, it cant flow back to nucleic acid.” The discovery of retroviruses, which transcribe RNA into DNA through the use of a special enzyme called reverse transcriptase threw off the central molecular dogma. HOMEWORK ASSIGNMENT WEEK 3 1) Approximately how large is the HIV genome? How many genes and corresponding proteins does the genome encode? Describe the main categories of genes and the main functions of the HIV proteins. The HIV genome is 9749 nucleotides-- about the same size as any other retrovirus. It is around 120 nm in diameter (120 billionths of a meter; around 60 times smaller than a red blood cell) and roughly spherical. HIV contains 10 genes namely gag, pol, env, tat, rev, nef, vif, vpr, vpu, and vpx. It should be noted that vpu is not present in HIV-2, while vpx is not present in HIV-1. The gag genes encode four proteins namely p24, p6, p7, and p17. These proteins provide the structural elements of the virus—p24 makes up the viral capsid, p6 and p7 provide the nucleocapsid, and p17 provides a protective matrix. Pol also encodes four proteins: reverse transcriptase, which copies the virus genome into the RNA; protease, which processes proteins made from HIVs genome so that they can become part of new fully-functioning HIV particles; RNAse H, which breaks down the retroviral genome following infection of a cell; and integrase, which which integrates the DNA copy of HIVs genome into the host DNA. Env encodes a single protein gp160 which travels to the cell surface, where cellular enzymes again attack it, parting into proteins namely, gp120, and gp41. Gp120 forms the virus spikes while g41sits inside the cells membrane being anchored to gp120. Tat encodes a protein also called tat (Trans-Activator of Transcription which helps HIV reproduce by compensating for a defect in its genome. Rev (Regulator of Virion) protein stimulates the production of HIV proteins, but suppresses the expression of HIVs regulatory genes. Nef (Negative Replication Factor) hangs around in the cytoplasm of the cell, and retards HIV replication. The vif gene codes the vif (virion infectivity factor) which increases the infectivity of the HIV particle. On the other hand, vir (viral protein R) accelerates the production of HIV proteins. Vpu or viral protein U helps with the assembly of new virus particles. VPR stands for “Viral Protein R” and plays an important role in regulating nuclear import of the HIV-1 pre-integration complex, and is required for virus replication in non-dividing cells such as macrophages. 2. List and describe the major steps in the HIV life cycle. 1.Viral Attachment—the HIV finds a host by attaching itself to the body’s T-cell or CD4 cells. 2. Viral Fusion—once attached to the cell, HIV injects proteins of its own into the cellular fluids (cytoplasm) of the T-cell. 3. Uncoating—the protective coating surrounding the RNA is dissolved allowing the conversion of RNA into DNA 4. Reverse Transcription—the single stranded RNA of the HIV is converted to the double stranded DNA. 5. Integration—the newly formed DNA is integrated into the cell nucleus 6. Viral Latency—HIV must wait for more protein building blocks to be formed by the cells 7. Final Assembly—when protein materials are already available, the virus separates and assembles into new HIV 8. Budding--the newly formed HIV pinches off and enter into circulation, ready to start the whole process again. 3) What are the four major stages of HIV/AIDS disease? Describe what is happening with the virus and the host during the major stages. What is meant by the term “wasting”? How long can an HIV-1-infected person live? During which stage(s) can HIV be transmitted? What are the main prognostic markers of HIV disease progression - which is the best indicator? There are four major stages of HIV. The first is acute HIV syndrome where the virus rapidly spreads to organs, especially in the lymphoid tissues but is not yet aggressive in causing disease or severe symptoms. The second stage is asymptomatic stage where the virus starts to grow and multiply in the lymph nodes, but the infection is latent. In the third stage, an individual has attained full-blown AIDS and begins to lose immune system function mainly due to the infection of CD4+ T-lymphocytes. The fourth stage is the end-stage disease where the virus continuously destroys the immune system which can last for ten years. The transmission of HIV is highest in the first and second stages of infection. A person diagnosed of HIV-1 can live 8-10 years on the average. The pathogenesis of HIV infection is a function of the virus life cycle, the host cellular environment, and quantity of viruses in the infected individual. Factors such as age or genetic differences among individuals, the level of virulence of an individual strain of virus, and co-infection with other microbes may influence the rate and severity of disease progression. However, viral load is considered as the best indicator. 4) What are the major mechanisms by which HIV destroys target (CD4) cells? 1. Direct cell killing. Infected CD4+ T cells may be killed directly when large amounts of virus are produced and bud off from the cell surface, disrupting the cell membrane, or when viral proteins and nucleic acids collect inside the cell, interfering with cellular machinery. 2. Syncytia formation. Infected cells also may fuse with nearby uninfected cells through CD4-mediated fusion, forming balloon-like giant cells called syncytia. This mechanism of cell-to-cell spread of HIV has been associated with the death of uninfected cells. The presence of syncytia-inducing variants of HIV has been correlated with rapid disease progression in HIV-infected individuals. 3. Apoptosis. Infected CD4+ T cells may be killed when cellular regulation is distorted by HIV proteins, probably leading to their suicide by a process known as programmed cell death or apoptosis. Uninfected cells also may undergo apoptosis. Investigators have shown in cell cultures that the HIV envelope alone or bound to antibodies sends an inappropriate signal to CD8+ T cells causing them to undergo apoptosis even though not infected by HIV. 4. Innocent bystanders. Uninfected cells may die in an innocent bystander scenario: HIV particles may bind to the cell surface, giving them the appearance of an infected cell and marking them for destruction by killer T cells. 5. What are the major components of the immune response to HIV infection? Why are antibodies not able to eliminate the virus? The response comes in two forms: cellular and humoral. The cellular response refers to the activity of the CD4 and CD8 T-cells, while the humoral response refers to antibody production and activity. HOMEWORK ASSIGNMENT WEEK 4 1. What is the main mode of HIV transmission in the United States? What is the main mode worldwide? Which mode of HIV transmission is associated with highest risk of HIV infection and which is associated with lowest? Comment on the amount of risk associated with heterosexual transmission of HIV when compared to actual numbers of global infections. In the United States, the main mode of HIV transmission is the unprotected sexual intercourse between men. Worldwide, unprotected sex remains the main mode of HIV transmission. Infected blood, semen or vaginal secretions presents the highest risk while oral sex presents the lowest risk. Heterosexual intercourse can be very risky especially as unprotected heterosexual intercourse is the primary mode of HIV transmission globally. 2. What is a coinfection? How can these infections affect the course of HIV disease? Include a discussion of the term “virulence”. Coinfection is the process of simultaneous infection of a single cell by two different viruses. For example, a person infected with HIV is also exposed in having hepatitis. Coinfection is seen to favor higher virulence which describes the ability of virus to cause diseases. In the case of HIV, coinfection with other viruses significantly lowers the immune system making the body more susceptible to other diseases. 3. In the U.S., we have seen increased rates of infection in specific populations, including the military, college students, and prisoners. Discuss what issues have contributed to the trends seen in these groups. There have been a significant increase infection in the military are they are continuously exposed to areas where AIDS is prevalent. The current trends among college students like sharing needles used to inject drugs or other substances and unprotected sex increase the risk of acquiring HIV. In the case of prisoners, the transmission of HIV is more prevalent with the popularity of homosexual sex. 4. At which points during (or after) pregnancy can an HIV-infected mother transmit the virus to her baby? Are all points associated with an equal risk of transmission? What factors have been associated with increasing risk for transmission? What measures have been scientifically shown to reduce transmission risks at the different points? A mother can transmit HIV to her child during pregnancy, at birth, and through breastfeeding. The risk is highest during pregnancy as the baby and the mother constantly have an exchange of blood. It has also been found that HIV transmission is more likely is the mother is already in the late stages of AIDS. Other factors are: viral, bacterial, or parasitic placental infection, for example, malaria during pregnancy; obstetrical and gyneconological; and amniocentesis, placenta previa, abruptio placentae, fetal scalp monitoring, episiotomy, and second-degree tears of the birth canal. A study shows a reduction of maternal-infant transmission rate from 26% to 8% if the infected mother receive zidovudine therapy during 14 weeks gestation to 34 weeks gestation, during delivery and the new born baby take a course of zidovudine for six weeks. 5. What major factors in the viral life cycle contribute to viral diversity? What is the major subtype that is circulating in Sub-Saharan Africa? What is the major subtype circulating in Europe and the U.S.? Viral diversity can be explained by the factors influencing the life cycle of the virus like the co-receptor status of the CD4 cells and presence or absence of co-receptor mutations. Generally, viral diversity can be explained by the process of mutation and recombination. In Western Europe and the Americas, the HIV-1 epidemic is largely dominated by B subtype viruses; while in Sub-Saharan Africa HIV-1 epidemic is largely dominated by A subtype viruses. WEEK 3 DISCUSSION-Q1 When a person thinks that they might have been exposed to HIV and are tested for infection, they are often told to return for another test in about 6 months. Based on what you have learned this week, what is the biological explanation underlying this clinical recommendation? The HIV test looks for antibodies in a persons blood. When HIV (which is a virus) enters a persons body, special chemicals are produced called antibodies. So if a person has antibodies to HIV in their blood, it means they have been infected with HIV. Most people develop these antibodies within 3 months of infection. In rare cases, it can take up to 6 months. It would be extremely uncommon to take longer than 6 months for antibodies to develop. Getting tested earlier than 3 months may result in an unclear test result, as an infected person may not yet have developed antibodies to HIV. It is also important that you are not at further risk of getting infected with HIV during this time period so you need to wait for six months. The test is only accurate if there are no other exposures between the time of possible exposure to HIV and testing. WEEK 3 DISCUSSION-Q2 Imagine you are working for a pharmaceutical company designing drugs that target HIV. Given what you have learned this week about the HIV life cycle, what steps of the life cycle would you like to target in your drug design and why? (FYI: We will be covering HIV drugs in a few weeks- so, this is just really meant for discussion. You do not need to spend hours researching this topic right now.) If I am going to design a drug for HIV, I will choose to attack the virus during the viral fusion. In this process, I would like to have a drug which will enable the cell to repel or dissolve the proteins injected by the virus into the cell. WEEK 4 DISCUSSION-Q1 Go to the internet, a newspaper or any other type of journal/periodical from the past month and find an article about some HIV-related statistic or something that affects the epidemiology or transmission of HIV. Tell your classmates (and me!) about what youve learned and also tell us where you read this. This information comes from an article entitled “HIV over 50) from About.com (http://aids.about.com/cs/aidsfactsheets/a/seniors.htm). The current mindset is that HIV cases are prevalent only on demographic groups under 50. However, it should be noted that the 50+ population accounts for 11% of the total number of AIDS victim. One myth which contributes to this false belief is that individuals aged 50 are unlikely to have sex. Well, this is wrong as it has been proven that the desire for sex will wane only after reaching 50. It is also found out that the 50s population comprises the 10% of the total number of AIDS victim in 1980s. Blood transfusion was the major cause, but now, heterosexual intercourse is now the main mode. The author prescribes three ways in how to cope with this issue: first, the traditional mode of thinking should be changed; stereotypes must be broken down; and provide seniors with the knowledge that they need to combat AIDS. WEEK 4 DISCUSSION-Q2 On the slide about modes of HIV transmission, why did I put a question mark next to "kissing"? Kissing is not a potent mode of HIV transmission. WEEK 4 DISCUSSION-Q3 What does the 80/20 rule refer to? How does this concept apply to HIV transmission? The 80/20 Rule. It says that 80 percent of an epidemics new infections will be spread by just 20 percent of the infected population. Read More