Two weeks of breeding and feeding the virus! : Part 2

Every human being has a reservoir of cells of the immune system (T-cells and B-cells). These cells usually are in a virgin state; that is, they would not have encountered any infectious material; therefore do not know anything about any organism. These reservoirs are called lymph nodes. The ones we are most familiar with are the tonsils and those on the inner side of your thighs which when you have a wound on your leg are also painful (mwandabvu)

The constabulary of the immune system (dendritic cells, macrophages, langerhans cells) swim to these lymph nodes which act as the Central Police Station. I want you to visualize this setup. In this police station are the Detectives or CD4 (T-Helper) cells which before the entry of the constabulary are relaxed and do not know that such thieves as the one held by the constabulary cell exist. There are also amateur recruits that know only to deal with a single kind of crime each (B-cells). If they are programmed to deal with thieves, when they meet murderers they just leave them.

Now, when the Constabulary gets into the Police Station with the thief, the new recruits (B-cells) rush to scrutinize the thief wanting to check if he/she falls within their specialty. Once it is discovered that indeed it is the one; that B-cell swallows the virus and continues to bash it with chemicals until the proteins that make up the outer coat of the virus are degraded to just small chunks called peptides. If we were to continue with our example, these B-cells would, instead of going to the Detective with the thief, they would rather chop the thief into pieces then present maybe the leg or the buttocks and say "All cellphone thieves have this kind of legs or buttocks; so what should we do?”

The Detective scrutinizes the leg and if he is satisfied that indeed the thieves bear such features, he simply sends a directive in the form of chemicals called cytokines which tells the new-recruits to unleash all the dogs they have and to wake up all the other recruits who could be sleeping. These dogs would also be programmed to only catch those people with specific features and they are called Antibodies.

So B-cells function to produce antibodies that are specific to HIV. These antibodies now bind to the outer coating of the free-floating virus thereby alerting other cells that “Here with me is a foreigner called HIV”. This is called tagging. Once the tagging is successful, the free virus is then swallowed by macrophages or the virus is destroyed by another way which I think is beyond the scope of our discussion but for your benefit is called the Complement system.

Here the CD4 cell functions to amplify the B-cell response.

The antibodies are what people at the HIV testing centers would be looking for. If you have them it means that your body was once challenged by the HIV and it responded by sending out these markers to detect the virus and usually they begin to appear in detectable quantities after 2 weeks. That is why when you are exposed to the virus and you go for testing they ask you to return after 2-3 weeks.

Generally what I have described above is what happens when a person is infected by any foreign agent. Usually, the body is successful in eliminating the infectious material in this way but when it comes to HIV, there are many complications that the body encounters.

Unfortunately, when the Dendritic Cells or Langerhans cells capture HIV at the point of entry and begin to bash it, the virus releases its genetic material (RNA) . Now, the virus has an enzyme(Remember Form 1 Science: An enzyme is a substance that is able to speed up a rection or process!), this enzyme is called Reverse Transcriptase and its function is to assist the cell to form DNA(normal genetic material in living cells) from RNA(the viral genetic matter.) This process is called Transcription.

Once this DNA is inside nucleus of the cell it begins to be integrated into DNA of the host cell. I hope you know that the purpose of the DNA is to direct the cell on what kind of proteins to make. Now because the cell now also has the viral DNA, it also begins to make viral proteins. At this point viral replication begins. So, I hope you have realized that when the Constabulary captures the virus he is fooled into beginning to make more viruses before he reaches the Police station. By the time our beloved constabulary reaches the police station he would probably have produced thousands more HIV particles. That’s how smart HIV is and how foolish our bodies are!

Now, to make life even difficult for our bodies; this HIV has got a great affinity (liking) for the CD4 glycoprotein that is found on all CD4 positive cells (T-helper cells). Once it binds to such a cell it is swallowed and the cell goes haywire and begins to produce viruses. So the cycle continues.

Remember we once said there are other T cells which are not CD4 cells but are CD8 cells (T-cytotoxic cells). Their function is to kill any infected cells. So once they come in contact with any CD4 cell that is infected, it is immediately killed or is influenced to commit suicide. HIV can also influence CD4 cells to bind each other resulting in their death. (Syncytia formation).

That is how HIV infection reduces the CD4 cells in our bodies and that is why CD4 cell monitoring is important because it tells us the state of our immune system. A low CD4 cell count signals the need to boost the immunity or to reduce viral multiplication.

If you are an HIV-patient: do not forget to regularly monitor your CD4 cell count. If you are taking care of an HIV-positive relative---Don’t let it until too late to have his/her CD4 count checked.

Lets meet in the next topic: HIV does not kill, it facilitates death!

Two weeks of breeding and feeding the virus! : Part 1

In the first two articles we noted how HIV penetrates the vaginal or penile mucosa (skin), we also discussed the risks associated with Oral Sex. These are not the only routes of infection: we have direct injection of infected blood like in cases of needle-stick injuries, we have mother-to-child transmission during pregnancy and we also have anal transmission in homosexuals and those who engage in anal sex. It has been proved that anal (rectal) exposure has a greater risk than vaginal exposure but both have a much greater risk than oral exposure.

We also noted that both the foreskin and the vaginal mucosa are rich in cells called dendritic cells whose job is to capture any foreign object like bacteria and viruses. In our quest to follow the path that the Human Immunodeficiency Virus takes until somebody reaches full-blown AIDS let us examine what happens from here.

Before we jump into this, as aspiring virologists we also have to know how the blood is constituted. So for a short period we are going to be hematologists (somebody who studies blood!). This red fluid we call blood contains cells. Red blood cells (erythrocytes) give it the red color because of a chemical called hemoglobin whose function is to trap oxygen from the lungs and deliver it to other cells so that we can produce energy. We also have white blood cells whose function is to protect the body from infection. We have platelets which help in clotting when we bleed. Finally we have the fluid called plasma where everything swims in. One milliliter (1ml) of blood has about 6 billion red cells, 3 million white cells and 1,5 million platelets.

We are more concerned about the White Blood Cells (WBC) because we are worried about how a person can suddenly become frail and fail to defend himself from diseases. These WBC can also be divided into Lymphocytes (because they are associated with lymph nodes) , Granulocytes (because they have granules) and Monocytes ( because they have a single big nucleus). Don’t worry about the big names, they are only there to confuse you, I will explain to you what they all do.

Let us continue with the series and see how lymphocytes are subdivided. The family of lymphocytes is further subdivided into B-cells and T-cells. The “B” refers to a part found in birds called bursa of Fabricius where they mature, in human beings they are produced in the bone marrow and then move to the spleen where they mature. The T cells mature in the Thymus hence the “T”.

In HIV Sciences we are more concerned about this T- cell family and we will basically concentrate on them. However, I promised to explain the basic functions of Monocytes and Granulocytes. Monocytes are a family of white blood cells which swim in the blood looking for any damaged tissues. When they find this tissue they undergo a series of changes that result in them being called macrophages. These macrophages can engulf and digest any bacteria that may want to enter through the damaged tissue eg a wound. Their behaviour is similar to dendritic cells( Langerhans cells on the foreskin). When there is a wound and the bacteria is seeking to enter the body; macrophages and the injured tissue produce chemicals which call on Granulocytes to come and reinforce. These Granulocytes like Monocytes and Macrophages are able to swallow infection agents like bacteria.

Back to T-cells. How many of you have heard somebody saying “He is critically ill, actually his CD4 count was very very low?” Next time you hear them say CD4 blah blah just ask them , “You mean T-Helper cells?”

The T-cells are further categorized into T-Helper cells and T-Cytotoxic cells. The function of the T-Helper cell is to help the body to defend itself by stimulating other cells into action like the B-lymphocyte mentioned above. The T-cytotoxic (“cyto” means cell thus toxic to cell) assist in destroying other infected cells.

You see, on these cells there are certain clusters of glycoprotein (a protein coated with some sugar) attached to the outer surface. Now some Scientists decided to differentiate these clusters of glycoproteins by using numbers. So T-Helper cells carry one of this glycoproteins whose Identity Number is 4 (four). The complete name becomes Cluster Differentiation 4 or CD4 in short. Now just like we say a patient who has HIV infection is HIV-positive; we can also say a cell that carries a CD4 glycoprotein is a CD4 positive cell. That is why T-Helper cells are called CD4 cells and T-Cytotoxic cells are called CD8 cells. Just that!!!!!!!!.

We are now done with the hematology of HIV Sciences back to our beloved virus! The virus is now engulfed by the dentritic cell (Langerhan)or Macrophage . The behaviour of these cells is typically that of a Constabulary Policeman in Zimbabwe: when he catches you he beats you until you soften up and then he parades you to the Officer-in-charge; No Negotiations! These cells engulf the viral particle and begin to bash its outer coating with acids called lysozomes which are found within these cells. The ultimate goal is to present this intruder to the officer-in-charge who in this case is the CD4 (T-Helper) cell.

……….to be continued…………………..

Oral Sex: Who can eat HIV and survive!

Last time I dwelt on how HIV infects the vaginal or penile walls. A question that is always hovering in many discussions is whether HIV can be transmitted through oral sex.

First of all we need to understand that oral sex can be classified as receptive, meaning the act of inserting one’s penis into another partner’s mouth with ejaculation and also non-receptive meaning without ejaculation.

Is HIV transmissible without ejaculation?

There are studies which have shown that HIV can be transmitted through the anal route without ejaculation, however the cases that have been reported are very very rare. This is because it has been difficult to engage in studies where the subjects are controlled from ejaculation. Thus, it remains hard to clearly conclude whether HIV can transmitted orally without ejaculation. Please do not take this as a go-ahead to engage in unprotected oral sex because it has been proved that pre-cum also is potentially contagious!

… but what of receptive oral sex?

There is reasonable scientific evidence that HIV can be transmitted through receptive fellatio (oral sex). It has been shown in monkeys that if you expose their tonsillar tissue to SIV (Simian Immunodeficiency Virus which is nearly the same as HIV), the monkeys can be infected.

Data is also there about the histological make up of the animal tissues of the tonsils. The histology of the tonsillar tissue is identical to the histology of the vaginal and rectal tissue with high density of dendritic cells (which we talked about in the previous post) and M-cells which are also capable of transporting antigens (or viral matter) to lymphoid tissue resulting in infection.

This is just scientific evidence but it has been hard to actually pinpoint receptive oral sex as a major transmission route. This is so because, most people do not practice oral sex in isolation but mostly in conjunction with other riskier practices like receptive anal and vaginal sex.

Epidemiological studies have classified the risk of receptive oral sex as low, however the risk increases significantly if there are injuries to the mouth or in cases of oral thrush.

Let me end by saying, swallow the sperm at you own risk! Let’s meet in the next topic:
Two weeks of breeding and feeding the virus!