Human immunodeficiency virus, or HIV, only emerged in humans relatively recently, yet already represents a big public health threat. When HIV enters the human body, often through sexual contact or the sharing of needles between drug users, it shows a remarkably focussed preference for infecting a certain population of immune cells, known as CD4+ T cells. Since these cells usually play a major role in vanquishing a viral foe, this is the perfect spot for HIV to hide out, since it essentially disappears behind an immune firewall.
Once HIV infects a CD4+ T cell, it often stays silent for long periods of time. Eventually, though, it will begin to multiply in a process known as replication. We know that it takes about 24 hours for HIV to complete its replication cycle, producing lots of progeny viruses that spread through the entire body. Yet the exact stages and timings of this replication process are not very clear. Researcher’s in Switzerland have now determined that nine intermediate stages occur through a single 24 hour replication cycle. Timewise, 3 hours after first entering the CD4+ T cell, the virus begins processing its own genetic material to make it compatible with that of the host cell. At 4 hours, the virus orchestrates a huge shutdown of all normal host cell functions. Any host genes with the ability to attack and subdue HIV are particularly targeted. At 8 hours, the viral genetic material is forced into the DNA of the host cell. Viral data starts to be decoded, forming a blueprint that will guide construction of new HIV particles. At this point, the virus begins to switch certain cellular functions back on, to help viral replication. By 15 hours, all the component parts necessary to build new virus particles have been produced and at 18 hours, fully completed viruses are coming off the production line. They leave the nursery cell where they were created, and set about finding a new CD4+ T cell to start up their own replication cycles.
This research gives us an excellent insight into the life cycle of a single HIV particle. Knowing when each stage emerges during replication could help us apply targeted interventions, aimed at preventing the transition between certain stages and thus blocking viral reproduction. This may ultimately help to guide the development of better treatments.
Mohammadi P, Desfarges S, Bartha I, Joos B, Zangger N, Muñoz M, Günthard HF, Beerenwinkel N, Telenti A & Ciuffi A (2013). 24 Hours in the Life of HIV-1 in a T Cell Line PLOS Pathogens, 9 (1) : 10.1371/journal.ppat.1003161