Chapter 2: HIV: Biology and Safer Sex

 

Contents

The Basics on Viruses and HIV

The Immune System

How HIV Infection Occurs

Sexual Transmission Prevention Guidelines

How HIV is Transmitted Sexually

Condoms and Safer Sex

Sexually Transmitted Disease

 

Note: The terms T4-cell, T4-helper cell, CD4 cell, T4-lymphocyte, and CD4 lymphocyte are different names for the same white blood cell. The terms are interchangeable. Different health care providers may use any of the five terms when discussing this group of white blood cells. You will see all five terms used throughout this manual.

 

The Basics on Viruses and HIV

How Viruses Reproduce

Viruses are very simple living organisms. They consist of genetic material (RNA or DNA) and an envelope shell that encases the genetic material (see Figure 2). The envelope is generally made up of proteins and sugars. A virus cannot reproduce on its own. It needs a "host" cell in order to reproduce or make copies of itself.

All cells in the human body have DNA as their genetic material. DNA is the material that is responsible for directing the production of new cells.

A virus whose genetic material is DNA would infect a host cell by injecting its viral DNA into the cell. Then, through a series of events the viral DNA becomes part of the cells DNA. The cell no longer makes copies of itself, instead it "unknowingly" becomes a "virus factory" and makes copies of the virus that infected it.

HIV Reproduction

Not all viruses have DNA as their genetic material. Some have a different substance called RNA. RNA is the mirror image of DNA. RNA contains genetic codes, but the structure and makeup are different and RNA can not direct the production of new viruses.3

This group of viruses, whose genetic material is RNA, is called retrovirus. The Human Immunodeficiency Virus or HIV belongs to this family of viruses. Like all viruses, HIV depends on the cells it infects to make new copies of itself. One of the main targets of HIV is a white blood cell called a CD4 cell (see Figure 1).

HIV infects a CD4 cell by attaching itself to the surface of the cell and injecting its genetic material (RNA) into the host cell (see Figure 3). Since RNA can not direct the reproduction of new viruses, HIV must first turn its RNA into DNA. 1 HIV turns its viral RNA into a viral DNA copy through the use of an enzyme called reverse transcriptase. This process is know as "reverse transcription" (see Figure 4). Once the conversion process is done, the viral DNA may become part of the host cell’s DNA. This process is known as "integration". At this point infection is complete.1,2

Once the viral DNA copy is successfully made part of the infected cell’s DNA, the infected cell goes on to produce new HIV every day. As many as 10,000 new HIV copies can be produced before the infected CD4 cell is destroyed. The new copies of HIV then go on to infect other cells. In this way, HIV spreads throughout the body. This allows for billions of new viruses to be produced every day.1,2,3,4

Forced to manufacture new HIV (viral replicas), the host cell neglects its own life processes. Gradually, like a machine wearing out, the CD4 cell starts to fail and dies.

The body can fight HIV infection effectively for a long time, replacing infected CD4 cells with as many as two billion new, uninfected cells every day. Sooner or later, however, the immune system begins to weaken. Gradually, the number of CD4 cells (T4-helper cells) available to fight infection becomes smaller and smaller, while the amount of HIV increases. As the number of HIV increase and the number of CD4 cells decrease, the body begins to become vulnerable to disease and infection.1,2,3,4

The fact that HIV uses the body's own genetic material to make copies of itself makes it difficult to develop a vaccine or to find a cure for HIV infection. A vaccine developed from one strain of the virus is useless when it mutates, and another vaccine has to be developed. There are drugs and medications that slow down the replication of the virus. However, nothing "kills" it completely.

The Immune System

The following explanation of the immune system was taken from the "Volunteer and Staff Training Manual" produced by AIDS Foundation San Diego.5

Several cell types in the human body serve as homes for HIV. Most of these cells are parts of the body's immune system. The immune system defends the body from disease. It is composed of a number of specialized cells, several organs, and a group of chemicals that are made by the body. The human immune system is like a wall that protects us from armies of germs. This wall can be compared to a jigsaw puzzle -- many parts fit together to form a solid surface. If pieces are missing or damaged, germs rush in through the holes. This happens with AIDS.

Over most of the body, the skin prevents germs from entering the body. So, germs can enter only through a body opening, cut, or wound. Once inside the body, germs trigger the immune system into its "fight mode", this is also called an immune response. All cells belonging to the body have special molecules on them that are like flags with the word "friend" on them. The cells of the immune system try to destroy anything present in the body that is not carrying a friendly flag, anything that is "non-self." Any substance or object that triggers the creation of antibodies is called an antigen. Antigens may be whole germs, parts of germs, or some germ product. Antibodies are discussed below.

 


How HIV Infects CD4 Cells and Makes Copies of Itself

 

Figure 1. CD4 or T-helper cell. This is HIV’s favorite cell to infect.

 

 

 

 

 

 

 

 

  

 

 

Figure 2. HIV. HIV consists of a outer shell and its genetic material.

 

 Figure 3: HIV attaches to the CD4 cell (T-helper cell)

 

 

 

 

 

 

 

 

 

Figure 4: HIV injects its viral RNA (blue) into the cell. The viral RNA is then changed into a double strand of viral DNA (Blue-dark blue). The doulbe strand of viral DNA moves into the nucleus of the CD4 cell and becomes part of the CD4 cell's own DNA (blue and red). The CD4 cell is then forced to make copies of HIV, unles the cell is latently infected.

 

 

 

 


T-cells

In the human body there exists a group of white blood cells called the lymphocytes, or T-cells for short. They are called T-cells because they are made in the Thymus gland. Among the T-cells, the T4-cell is HIV's favorite; that is, HIV easily infects and replicates in the T4-lymphocyte.

The T4-lymphocyte, also called the "helper T-cell," performs an important job in the immune system. It finds germ invaders by circulating through the blood stream and bumping into them. After finding an invader, T4-cells release chemicals which trigger other parts of the immune system into action against the invader. In response, lymphocytes and other immune cells rapidly grow in number. Some of these cells directly attack the invader. Some are lymphocytes that keep sounding the alarm to draw other cells into the area. The T4-cell recognizes viral, fungal, and parasitic invaders and triggers only those portions of the immune system that act against these invaders.

Another lymphocyte is the T8-lymphocyte or suppresser T-cell. T8-cells balance the action of T4-helpers by releasing chemicals to block the effects of the T4-cell's alarms. Together, T4-cells and T8-cells regulate the body's immune response to invaders. Also, T8-cells help the immune system recognize (and not attack) the cells of its own body.

T-cell Function and HIV

Once HIV hijacks a T-cell the lymphocyte stops working well, although this change doesn’t show right away. HIV's takeover is a quiet event. The virus' RNA reverse transcribes its DNA partner, then - nothing happens. Evidently, very little or no viral replication takes place until the host T-cell is activated by some antigen. Then, instead of functioning normally, the T-cell manufactures the invader's viral RNA strands. The activating antigen does not seem to be another HIV but some unrelated stimulus such as viral, fungal, or parasitic invader.

The "opportunistic diseases", common in AIDS, prove the T4-cell population is not working properly. The opportunistic diseases seen in AIDS are caused primarily by fungi, viruses, and parasites, many of which we encounter daily. Some of these organisms live permanently in our bodies, although in healthy people they are held in check by a correctly functioning immune system.

HIV infection kills T-cells. So in addition to poor T-cell performance, the actual number of T4-helper cells in an infected person decreases. How HIV kills cells is not clear. There is evidence that HIV increases the natural dying process of cells ("programmed cell death").

Some T8-suppresser cells also die during HIV infection. The immune system is not properly suppressed in some infected patients and they may have an auto-immune response, meaning that parts of their immune system attack their own bodies.

Macrophages

HIV is able to infect and replicate well in macrophages. Macrophages are large white blood cells that swallow and digest germs and other microscopic invaders. It is possible that HIV is eaten by the macrophage and hijacks the cell from inside.

Macrophages are called monocytes when they are circulating in the blood. Monocytes change into various types of macrophages (with different names) in order to perform search-and-destroy missions within tissues of the lung, brain, and interstitial (tissues connecting the organs) regions. Despite the name changes, all forms of macrophages basically work the same way: they eat things. Some macrophages travel around within the body; others become attached to one spot, eating what comes by.

Macrophages are often the first scouts of the immune system to encounter germs, particularly in the area of a cut or wound. After engulfing the germ, the macrophage makes copies of the germ's epitopes (structures on the surface of the germ or invader) and displays them on its own cell membrane. These copies of the germ epitopes sit right next to the "friend" flags. In effect, the macrophage makes a "wanted poster" of this new germ. The macrophage then travels about showing the wanted poster to T4-helper cells, which triggers the T-cells into action. Macrophages also release chemicals that stimulate both T-cell and macrophage production and draw macrophages and lymphocytes to the site of infection.

HIV infection does not seem to kill macrophages. In some infected human patients, HIV appears to change monocyte function slightly, not affecting the ability to engulf germs, but affecting the release of communication chemicals. In HIV-infected macrophages, the transformation from monocyte to another of its specialized forms seems to be the trigger of viral replication. Macrophages can produce high levels of virus for a long time in laboratory conditions.

In living beings macrophages may play an important role in spreading HIV infection in the body, both to other cells and to HIV's target organs. First, HIV quietly spreads from macrophage to macrophage before any other cells of the immune system notice. Second, macrophages, in their different forms, travel to the brain, the lungs, the bone marrow (tissue in the hollow centers of some bones), and to various immune organs, and bring HIV along with them. HIV's ability to infect brain tissue is particularly important. The brain and cerebral spinal fluid (CSF) are vulnerable sites, and, therefore, are specially protected sites. CSF cushions the brain and the spinal cord from sudden and jarring movements. The brain-blood barrier, a physical phenomenon, normally stops foreign substances from entering the brain and the CSF. Unfortunately, HIV-infected monocytes can slip past this barrier. For HIV, macrophages may be Trojan horses, enabling HIV to enter the immune-fortified domain of the central nervous system -- the brain, the spine, and all nerves. Once in brain tissue, monocytes change into microglial cells. In addition to acting as an immune system scout, microglial sells may make a number of regulatory molecules that balance immune system function and perhaps other functional systems.

HIV taken from macrophages seems to grow better in macrophages than in lymphocytes. In human experiments HIV taken from lymphocytes seem to grow better in lymphocytes than in macrophages. These features of replication are evidence of different HIV strains.

B-cells

The B-cell, another type of lymphocyte, is another component of the immune system and is a the key player of the "humoral" or antibody side of the immune response. B-cells require T4 cell help to respond effectively to new stresses or "antigens." B-cell function is abnormal in HIV infection.

According to laboratory evidence, HIV may infect B-cells. B-cells, triggered by the chemical alarm of T4-cells, rapidly grow in number and manufacture millions of antibodies, discussed in detail in the next section. It is possible that B-cells can be activated directly by virus antigens; the evidence is not yet conclusive.

It appears that HIV cannot normally enter and infect B-cells. However, in laboratory experiments, HIV is able to infect B-cells, if the B-cells are first infected by the Epstein-Barr virus, which is the cause of infectious mononucleosis. The Epstein-Barr virus appears to change B-cells in some way, allowing subsequent HIV infection. Whether similar events occur in humans is not known.

Antibodies

Antibodies are proteins that stop germs. Antibodies prevent viruses from attaching to the membrane, or outer covering, of the host cell. Viruses and antibodies fit together like pieces of a puzzle. Antibody molecules physically and chemically fit the molecules in the virus' protein coat. New antibodies must be tailored for each new germ.

B-cells make antibodies and release them into the blood stream. After being triggered by antigens or the T4-cell alarm, B-cells multiply and manufacture tailor-made antibodies to stop the new germ.

After an antibody and virus join, they are eaten by macrophages or cleared from the blood by the liver and spleen. Some B-cells become memory cells that are stored by the immune system. Memory cells remember the antibodies they have created. If the same virus ever gets into the bloodstream again, these cells rapidly begin antibody production. However, if the virus has mutated, as the flu does in its yearly journey around the world, the old antibodies cannot stop it. New antibodies must be created to neutralize the new mutant virus. While this antibody production is taking place, the viral invader has time to multiply and gain a foothold, and the infected person suffers the symptoms of the flu.

Antibodies and HIV

The human body makes HIV antibodies, but they seem not to work well. The HIV antibody works against HIV in a laboratory dish, but things rarely occur in life the same way they do in the laboratory.

In several experiments where HIV has been isolated from blood, large numbers of HIV antibodies were also found. This indicates that, even though the HIV antibody is present, it has difficulty latching onto the virus, and, therefore, provides little protection.The human body creates antibodies directed against a number of HIV proteins, namely the envelope proteins (gp120), the transmembrane protein (gp41), and the proteins of HIV's core (p24).

Antibodies cannot enter blood cells. An antibody can only attack viruses in the space outside of cells. Extra cellular fluid is the fluid space outside of the cells. Once inside a host cell, HIV has less to fear. Cells can generate anti-viral chemicals within themselves, but these too often seem ineffective against HIV.

Once a virus gets inside the host cell, it is likely to remain there for the rest of the host's life unless some other anti-viral mechanism within the body or some ingested chemical is able to destroy the virus or the infected cell.

In summary, the immune system protects the body, both inside and outside, from bacteria, viruses, parasites, fungi, and other antigens that could cause infection and disease. There are parts of the immune system, such as skin and fingernails, which are on the outside of the body, and parts, such as white blood cells, which are on the inside. "Antigens" are the bad guys, that is, the bacteria, viruses, and infections, and the "antibodies" are the good guys - they fight off the infections or "antigens." Occasionally, antibodies will attack a person’s own tissues and cells. This is known as an auto-immune disease (see glossary).

There are specific antibodies for specific antigens. For example, there are antibodies to fight off viruses that cause the common cold, flu, or even pollution in the air. When HIV infection occurs, the CD4 cell signals the body to produce antibodies. Unfortunately, the antibodies produced against HIV do not completely get rid of it. Varying and often high levels of HIV remain in the lymph nodes and blood, continuously copying and making it increasingly difficult for the body to fight off other infections.3

When people are tested for HIV, the test is actually measuring the immune system's production of antibodies to HIV. A positive test result means that your body's immune system has produced antibodies, so the immune system needs all the help it can get to keep you strong and healthy. It is important that you eat nutritious meals, get plenty of rest, and take your medicines regularly.

 

How HIV Infection Occurs

The Human Immunodeficiency Virus (HIV) is transmitted from one person to another in certain specific ways:

 

Sexual Transmission Prevention Guidelines

 

SAFE SEX

Abstinence, or any erotic, sensual, or sexual activity that cannot possibly involve mucous membrane exposure to blood, menstrual blood, semen, pre-ejaculate ("pre-cum"), vaginal secretions, or breast milk.

UNSAFE SEX

Any activity that exposes mucous membranes to blood, menstrual blood, semen, pre-ejaculate ("pre-cum), vaginal secretions, or breast milk.

SAFER SEX

Reducing the risk of exposure to blood, menstrual blood, semen, pre-ejaculate ("pre-cum"), vaginal secretions, or breast milk through the consistent and correct use of latex condoms, dams, or gloves.

Mucous Membranes: Anus/Rectum; Vagina/Labia; Mouth/Tongue; Penis(opening/urethra); Eyes; Sores/Cuts

 

How HIV is Transmitted Sexually

There are high concentrations of HIV in blood and in the male reproductive fluid, semen. HIV is also found in vaginal secretions and breast milk. To a lesser extent, the virus has been isolated in saliva and other bodily fluids. Therefore, any exchange of blood, menstrual blood, semen, pre-ejaculate ("pre-cum"), vaginal secretion or breast milk is considered risky behavior, though some behaviors or activities are higher risk than others. Thus far in the AIDS epidemic, there have been very few if any cases of anyone being infected with HIV through saliva, tears, urine, feces or sweat. However, you still need to think about and talk with your partner about the risk involved before sexual activity begins. The following explains the risk associated with certain activities.3,6

 

 

The American Association of Physicians for Human Rights (AAPHR) issued "refined" guidelines in 1990 on the risk of transmission from sexual activities, including oral sex. All types of oral sex were rated as having "some risk," compared to various forms of anal and vaginal intercourse, which were all ranked as "high-risk" behaviors.

The possibility of infection can occur as follows: HIV in semen or pre-ejaculate ("pre-cum") ejaculated into the mouth can be absorbed through the mucosal lining of the mouth, throat, gums or through small breaks and cuts present in the mouth, gums, and throat, thereby causing infection. Blood present in the mouth can be absorbed through sores, tiny cuts or breaks on the tip or shaft of a man’s penis or through the mucosal tissue lining the opening at the tip of the penis/urethra. If HIV is present in vaginal secretions, HIV can be transmitted to the partner of the HIV infected woman through the mucosal lining of the mouth, gums, and throat -- as well as any cuts, breaks, or sores on these tissues. HIV infected blood present in the mouth can be absorbed through the mucosal tissues of the labia, vagina, and clitoris or through sores, tiny cuts or breaks in these areas.

 

Condoms and Safer Sex

Condoms come in a variety of sizes and colors. In an age of HIV/AIDS, condoms are an absolute necessity for sexually active men and women. They offer the only protection against HIV infection. If you use a lubricant, make sure that it is water-based. Anything else, such as oil, hand lotion, Vaseline, or Crisco will cause the condom to break. Read the labels of any lubricants you may purchase to make sure it is compatible with a condom. If the condom breaks, it offers no protection against possible transmission of HIV or other STDs. Animal skin condoms, such as sheep skin, are not recommended since semen can seep through them and infect your sexual partner. Condoms provide a barrier between you and your sexual partner. There is a five percent error margin which results in condom breakage. Thus, the reliability of a condom is something to consider. However, with care, experience, and learning how to put on a condom correctly, a person should be able to improve on the 95% effectiveness rate. Here are some tips on condom use:7,8

Some people do not like to use condoms because they feel that condoms take away from the pleasure during sex. However, the idea is to make condoms a part of love-making and a regular part of sexual intercourse. There are ways of doing that if you are creative. Here are some condom tips:

Condoms can be purchased almost any where. Most county health departments give them away free. In Hillcest there is a store called "Condoms Plus." The sales clerks are very knowledgeable about the different types of condoms and lubricants and can answer your questions about which condom brands work best.

If you and your partner both have HIV, latex condoms must still be used during sexual intercourse, since there is a potential danger of re-infection. That is, there is a danger of giving MORE virus, possibly of a different, more virulent (stronger) strain, to your partner, whose immune system is already trying to fight HIV. More importantly, you could spread other infections that you (or your partner) don’t already have such has hepatitis A or B, CMV, and other STDs including the newly discovered Kaposi’s Sarcoma Virus (KSHV).

The Female Condom

Women now have the option of using condoms. A product known as the Female Condom, when used properly, can lower the risk of HIV infection and other STDs. The female condom is like a diaphragm, except it has a polyurethane sheath that protects the cervix, vaginal walls, and labia from exposure to semen. This device is particularly handy since in can be inserted into the vagina, like a diaphragm, several hours before sexual intercourse. Thus, the common complaint about condoms "interrupting the mood" is not an issue with this product. Also, it gives the woman more control over her own protection, since she no longer needs to rely on her male partner to wear a condom. These condoms can be purchased at drug stores like Save-On and Rite Aide under the brand name Reality Condoms.

Making a Latex Barrier for Vaginal or Anal Oral Sex

For vaginal or anal oral sex you should use a latex barrier. These barriers are more commonly called "dental dams" and can be purchased at Condoms Plus in Hillcrest. However, you can make your own barrier by taking an unlubricated condom and cutting off the tip with a pair of scissors, then cut the condom open and unroll it. The result will be a rectangle shaped latex barrier. You can then place this over the anus or labia/vagina of your partner (see figure below).

Sexually Transmitted Diseases

Sexually transmitted diseases are infections that are caused by microbes (germs) which are passed from one person to another during sexual activity (oral, anal, vaginal). People living with HIV might be more susceptible to infection and often have more serious cases. You can reduce your risk by using condoms and/or latex barriers for all sexual activity.

Chlamydia

Chlamydia is caused by bacteria called Chlamydia trachomatis . Symptoms of Chlamydia include a burning feeling when you urinate and a discharge from your penis or vagina. Many people don’t have symptoms, especially women. Chlamydia can also infect your throat, rectum and eyes. If left untreated it can cause serious infections both in men and women.9

Gonorrhea

Gonorrhea is caused by bacteria called Neisseria gonorrhea. It often does not cause symptoms in women. However, typical symptoms are a thick pus discharge from the penis or vagina and painful urination. Like chlamydia it can infect the throat and rectum. If left untreated it can spread to other parts of your body causing serious problems.9

Syphilis

Syphilis is caused by bacteria called Treponema pallidum. If left untreated syphilis can cause heart or brain damage and even death. The infection has three stages. The first is a sore that forms on the genitals, mouth, rectum, or throat. The sore will disappear on its own without treatment, but the infection is still active. The second stage happens up to six months after infection. It is characterized by sores or rash on the body. You may feel like you have the flu with headache and other aches and pain in the joints or bones. You may also experience flat wart like sores in your vagina or anus. These symptoms may come and go. The last stage of syphilis may take ten to thirty years. The bacteria infects the eyes, brain and heart causing blindness and damage to the heart and brain.10

Genital Warts

Warts are caused by a virus called HPV. The warts can be small or large and appear on your genitals, rectum or anus. Warts have been associated with cervical cancer in women and anal cancer in both men and women. In people with HIV the warts are often more severe. 9

Respecting Yourself and Others

Keep in mind that human sexuality involves a whole range of emotions. Sexual intimacy is one of the many expressions that give us pleasure. It is a healthy, normal expression and desire. However, sexual intercourse is not the "end all and be all" of human sexuality or expression, and sexual intercourse can sometimes be mistaken for love or substituted for emotional intimacy (feeling safe and connected to another person) and/or physical intimacy (hugging, touch).

It is important to be aware of your emotional and mental motivation for seeking out sexual intimacy. Your awareness can help guide you to getting your true needs met. Do you want intimacy? Do you want to feel loved? Do you want a relationship? Many of us want to experience our sexual expression within the contents of a loving relationship. Some of us don’t. Both are okay, if you are clear on what exactly it is you want. If you are honest with yourself and your partner then you will lessen the possibilities of harming either yourself or your partner both physically and emotionally.

Thus, getting to know your own feelings, thoughts, needs, and desires as well as your sex partner’s can deepen the relationship and create a safe environment for enhancing both your own and your partner's enjoyment of sex.

A big part of creating a more fulfilling sex life involves communication. Disclosing your HIV status to a potential partner can be intimidating and scary. A lot of us are afraid of being rejected by potential partners and sometimes we just want to have sex without thinking about HIV/AIDS. These are normal feelings. Yet, when you don’t disclose your HIV status and/or discuss safer sex with your partner the responsibility for your partner’s safety becomes yours. Unfair, you say. You’re right. But, it’s a sad and true fact that most people have a double standard when it comes to safer sex. What someone will do sexually if they think or are led to believe that his or her partner is HIV negative is usually very different from what someone might do if his or her partner is HIV positive. Once you have disclosed your status you can begin to make mutual decisions concerning what the two of you are comfortable with sexually. Below are some suggestions to help with disclosure:

Weather you choose to disclose your HIV status or not, it is important for you to protect your own health. If you are following the safer sex guidelines and use condoms for insertive and receptive anal, oral and vaginal sex you will be protecting yourself and your partner(s).

Talk to the Owen Clinic health educator (543-2680) if you have questions regarding safer sex, STDs, birth control, or any aspect of sexuality.


 

Chapter References

 

1. "The Battle Within: Current Concepts in the Pathogenesis of HIV Disease." A video distributed by Merck. 1997.

2. "The War on HIV." Published by Bristol-Myers Squibb. 1997.

3. Bartlett, John, M.D., and Finkbeiner, Ann. The Guide to Living with HIV Infection. John Hopkins Press. Third Edition, 1996. pgs. 58-64; 28-44.

4. Patterson, Brent and Robichaud Francis. Managing Your Health: A guide for People Living with HIV or AIDS. Canadian Edition. 1996. pgs. 15-20; 148-150.

5. "Volunteer and Staff Training Manual." Produced by AIDS Foundation San Diego. 1991.

6. "HIV Counselor PERSPECTIVES." UCSF AIDS Health Project. California Department of Health Services. Office of AIDS. Volume 1. Number 2. March, 1991.

7. "Talking With Your Partner About Safer Sex." Published by ETR Associates. 1994.

8. "The Safer Sex Condom Guide for Men and Women." Published by Gay Men’s Health Crisis. New York, NY. 1993.

9. " Sexually Transmitted Diseases: Facts." Published by ETR Associates. Santa Cruz, CA. 1997

10. "Syphilis." Published by the National AIDS Treatment Information Project. Boston, MA. 1996.


Please send any questions or comments to the Owen Clinic Webmaster.