1. How HIV affects the Immune System

2. INTRODUCTION HIV attacks and kills crucial immune system cells, known as T-helper cells. Without T-helper cells many other immune system cells cannot not work properly, including B-cells that make antibodies. A person infected with HIV may not show any symptoms for years. But untreated, the number of T-helper cells steadily drops. Eventually, the numbers fall so low that the risk of infection greatly increases, and the symptoms of AIDS appear.

3. Functions of T-Cells T-cells are a type of lymphocyte that co-ordinate the activities of the immune system They are the memory cells that store information about any antigens that previously entered the body They also kill cells that are local to the body and have been infected with germs

4. HIV has a core of genetic material surrounded by a protective sheath, called a capsid The genetic material in the core is RNA (ribonucleic acid), which contains the information that the virus needs in order to replicate and perform other function In HIV, the viral RNA has a protein called reverse transcriptase that is crucial for viral replication inside T cells HIV, like all other viruses, has proteins in the form of antigens that are particular to it. Antigens have diverse functions in viral replication. In the case of HIV, a combination of two antigens, gp120 and gp41, allow the virus to hook onto T cells and infect them. Structure of the HIV virus

6. HIV TARGETS T-CELLS T cells are the main target of HIV in the blood, and they act as the host that the virus needs in order to replicate. The T cell's DNA has all the information that the cell needs in order to function. The difference between RNA and DNA is that the former is a single strand of genetic material, while the latter is a double strand. This difference is crucial in the process of T cell infection by HIV.

7. The virus injects its RNA and reverse transcriptase into the cell The HIV virus attaches to the T-cell

8. Viral RNA needs to become DNA in order to start the replication process. Reverse transcriptase allows the RNA to borrow material from the cell and to "write backwards" a chain of viral DNA.

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