HIV virus

Introduction

The human immunodeficiency virus is a virus that works by infecting the body and attacking the immune system. It is an RNA virus that spreads rapidly throughout the body and causes abnormalities to occur within the immune system and its responses. This, in turn, can lead to other diseases and immune abnormalities. It has been linked to many other diseases, and has infected over 75 million individuals. The virus targets CD4⁺T cells. It then spreads rapidly in the coming days, until the infection plateaus, and the immune system regains some type of control. The virus is transmitted in many different ways, the most well known being sexual contact. Along with this, it can be transferred from mother to child or through needle exposure.

HIV is a single-stranded RNA virus with a diploid genome. The virus inserts parts of its genome into the host DNA, altering the genome of the host and using the host to create viral proteins. It then uses these viral proteins to infect other host cells and the cycle restarts.

If infected, constant treatment and medication can lower blood HIV levels. In fact, levels can get so low that the risk of sexual transmission is virtually zero. Certain regions have higher infection numbers, including the whole continent of Africa, especially Southern and Eastern Africa.

Infection and Immune Response

There is a small window of around 10 days after transmission of the virus where there is no viral RNA present in the body. The end of the eclipse phase is signified by a full body infection beginning in the draining lymph nodes. Cells that have already been infected travel to these nodes and come into contact with CD4⁺CCR5⁺T cells. The virus then infects these cells. Many immune cells, including macrophages, T cells, and others, are key points of infection, as they all express a certain receptor that is easily targeted by HIV viral cells. Once the virus has infected some cells, the spread is incredibly quick. Replication happens at an extremely fast rate. HIV spreads to any area of the body with high concentrations of CD4⁺CCR5⁺T cells, which includes lymphoid tissue present in the gut. A relatively small amount of cells in these tissues are actually infected. However, a large portion of cells that aren't infected are activated and go through programmed cell suicide, a process known as apoptosis. Because of this, a worryingly large portion of CD4⁺T cells become compromised within a very short frame of time, somewhere around 80%. Response from B cells are also interrupted during this phase of infection, though not because they are targets of infection. B cells are often matured in areas of the body such as lymph nodes and tissue, so the HIV infection in these places reduces B cell function and development.

There is often a small period where a patient may show symptoms of an infection, around the same time that the virus becomes detectable in the blood. Symptoms are typically not severe, just a small fever. Some patients show no symptoms at all, and some show more serious symptoms. This is also around the same time that blood levels are at their peak, around 10⁶ copies of viral RNA per 1 mL of blood plasma. Individuals with higher concentration of viral RNA will typically have stronger symptoms than individuals with a lower concentration. This level will decrease once the immune response occurs, until a set point is reached. Much like the initial symptoms, a higher set point is often correlated with individuals with rapid health declines.

Transmission

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Conclusion

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References

1. https://www.nature.com/articles/nature08237 2. https://www.nature.com/articles/nrdp201535

Edited by [Jp Timken], student of Joan Slonczewski for BIOL 116 Information in Living Systems, 2021, Kenyon College.