Question

With reference to HIV morphology and replication, explain how advances in anti HIV therapy has led to reductions in the mortal cases associated with HIV.

Answer 1

Ans) HIV stands for Human Immunodeficiency Virus, a pathogen that works by attacking the human immune system.
HIV specifically targets CD4 cells, the body’s principal defenders against infection, using them to make copies of themselves.
Antiretroviral drugs target specific stages of the ‘HIV lifecycle’ to stop HIV from replicating.

- HIV stands for Human Immunodeficiency Virus, a pathogen that works by attacking the human immune system. It belongs to a class of viruses called retroviruses and more specifically, a subgroup called lentiviruses, or viruses that cause disease slowly.

- HIV cannot replicate on its own, so in order to make new copies of itself, it must infect cells of the human immune system, called CD4 cells. CD4 cells are white blood cells that play a central role in responding to infections in the body.

- Over time, CD4 cells are killed by HIV and the body’s ability to recognise and fight some types of infection begins to decline. If HIV is not controlled by treatment, the loss of CD4 cells leads to the development of serious illnesses, or ‘opportunistic infections’. In people with normal CD4 cell levels, these infections would be recognised and cleared by the immune system.

- Experiencing a collection of these infections is the most advanced stage of HIV, which is when a person is also said to have AIDS (Acquired Immune Deficiency Syndrome). Effective testing and treatment of HIV means that the large majority of people living with HIV do not reach this stage.

- Although HIV can be controlled by antiretroviral therapy, it cannot be eliminated from the body. This is because HIV evades the normal immune system mechanisms for getting rid of cells infected by viruses.

- HIV integrates itself into the DNA of human immune system cells and only replicates when the cell is stimulated to respond to an infection. These cells are called latently-infected cells. These cells are not recognised as infected by the immune system and killed off, allowing them to persist for as long as the cell lives.

- Some of the cells infected by HIV are very long-lasting memory T-cells. Reservoirs of latently- infected cells become established in the lymph nodes, the spleen and the gut. HIV also infects cells in the brain, but it is unclear if HIV can pass from the brain to other parts of the body. HIV may also persist for many years in macrophages – immune cells found largely in tissues – and in dendritic cells, which recognise infectious agents and alert other immune cells to remove them.

- Latently-infected cells can proliferate without being activated and HIV may also pass from cell to cell within tissues in the gut and other reservoirs. 18 This means they evade the immune system and are not suppressed by antiretroviral drugs before infecting other cells.

- It’s unclear how quickly a reservoir of HIV-infected cells becomes established in the body. Observations in small numbers of people who have started antiretroviral treatment within a few days or weeks of infection show that they have fewer HIV-infected cells and if they stop antiretroviral treatment, some can control HIV for long periods without resuming treatment.