Sunday, September 20, 2009

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!