AIDS and Human Immunodeficiency Virus (HIV)
Acquired Immunodeficiency Syndrome (AIDS) is caused by infection with the Human Immunodeficiency Virus (HIV). Globally, HIV infection remains a major public health problem, with an estimated 34 million people infected worldwide. Approximately 70% of infected individuals live in Africa, while about 20% are in Asia. Since the beginning of the epidemic, over 30 million deaths have occurred due to HIV/AIDS, with around 2 million deaths each year. Despite this burden, the development of effective antiretroviral therapy has significantly improved survival and quality of life.
Human Immunodeficiency Virus (HIV)
HIV is a retrovirus that infects cells of the immune system, particularly CD4+ T lymphocytes, leading to their progressive depletion and immune dysfunction. Other important target cells include macrophages and dendritic cells, which play a key role in viral persistence and spread.
Structure of HIV
- HIV particles contain two identical strands of RNA enclosed within a protein core.
- The virus is surrounded by a lipid envelope derived from the host cell membrane.
- Embedded within the envelope are viral glycoproteins, most importantly gp120, which is essential for viral entry into host cells.
Life Cycle of HIV
The life cycle of HIV occurs in several well-defined steps:
1. Entry and Infection
- HIV infects CD4+ T cells, macrophages, and dendritic cells.
- Viral attachment is mediated by the envelope glycoprotein gp120, which binds to the CD4 receptor and specific chemokine co-receptors on host cells.
- Following receptor binding, the viral envelope fuses with the host cell membrane, allowing the virus to enter the cytoplasm.
2. Reverse Transcription
- Once inside the cytoplasm, the viral capsid is uncoated by viral protease.
- The viral RNA is released and converted into DNA by reverse transcriptase, a hallmark enzyme of retroviruses.
3. Integration
- The newly synthesized viral DNA enters the nucleus.
- Using the enzyme integrase, the viral DNA integrates into the host cell genome.
- The integrated viral DNA is known as a provirus.
4. Viral Gene Expression
- Infected immune cells may become activated by external stimuli such as other infections.
- Activation results in transcription of host genes and cytokine production.
- At the same time, viral genes are transcribed, leading to synthesis of viral proteins.
5. Assembly and Release
- Viral components assemble into a core structure.
- The virus buds from the host cell membrane, acquiring a lipid envelope.
- Newly formed infectious virions are released and can infect other cells.
- The provirus may remain latent for months or years, remaining hidden from the immune system and antiviral drugs.