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The genome and proteins of HIV (human immunodeficiency virus) have been the subject of extensive research since the discovery of the virus in 1983. [1] [2] "In the search for the causative agent, it was initially believed that the virus was a form of the Human T-cell leukemia virus (HTLV), which was known at the time to affect the human immune system and cause certain leukemias.
In contrast to the cell-dependent model, the cell-autonomous model proposes that HIV latency decisions are largely driven by the Tat-positive feedback loop and latency is therefore a probabilistic response due to intrinsically generated phenotypic heterogeneity rather than host-cell-determined. [12]
Continuous HIV replication results in a state of generalized immune activation persisting throughout the chronic phase. [6] Immune activation, which is reflected by the increased activation state of immune cells and release of proinflammatory cytokines , results from the activity of several HIV gene products and the immune response to ongoing ...
A simple negative feedback system is descriptive, for example, of some electronic amplifiers. The feedback is negative if the loop gain AB is negative.. Negative feedback (or balancing feedback) occurs when some function of the output of a system, process, or mechanism is fed back in a manner that tends to reduce the fluctuations in the output, whether caused by changes in the input or by ...
The words without arrows are loop labels. As with the links, feedback loops have either positive (i.e., reinforcing) or negative (i.e., balancing) polarity. CLDs contain labels for these processes, often using numbering (e.g., B1 for the first balancing loop being described in a narrative, B2 for the second one, etc.), and phrases that describe ...
An example that reveals the interaction of the multiple negative and positive feedback loops is the activation of cyclin-dependent protein kinases, or Cdks14. Positive feedback loops play a role by switching cells from low to high Cdk-activity. The interaction between the two types of loops is evident in mitosis.
Tat then binds to cellular factors and mediates their phosphorylation, resulting in increased transcription of all HIV genes, [4] providing a positive feedback cycle. This in turn allows HIV to have an explosive response once a threshold amount of Tat is produced, a useful tool for defeating the body's response. Tat also appears to play a more ...
These studies involved couples where one partner was HIV-positive and one was HIV-negative, and included regular HIV testing. Across these four studies, a total of 4,097 couples participated from four continents, reporting 151,880 acts of condomless sex with zero phylogenetically-linked HIV transmissions when the positive partner had an ...