HIV caught in the act

This week I’ve been watching invading microbes once again, but this time the bad guys win. The video above shows the spread of HIV between two cells. Made possible by a combination of technological and genetic engineering, it represents an important advance in understanding the behavior of these deadly infectious particles. A team of researchers altered the genetic code of a strain of HIV, inserting a protein that glows green under blue light, and then introduced cells infected with the altered virus into a culture of human T cells. Over the course of several days, they watched and photographed the results.

Viruses are parasites. They move into a cell and hijack its metabolic machinery to turn out multiple copies of the viral genome. Eventually the cell overloads and bursts, releasing the new viruses into the blood and lymph where they search for new host cells. This interval is a time of vulnerability – outside the protective membrane of a cell, the viruses can be attacked by the immune system and anti-viral drugs. (Witness the hapless bacteria in my previous blog.)

As this video shows, HIV spreads in a different manner, one that avoids the dangers faced by free-range viruses. An infected cell, colored green by its high HIV count, brushes alongside a healthy T cell, and a number of viruses gather just inside the cell membrane, along the contact point. The infected cell pokes the side of the T cell with a finger-like extension called a viral synapse, triggering the T cell to engulf the synapse and its deadly cargo.

This could be a very helpful discovery in the fight to combat AIDS. Attempts to develop an effective AIDS vaccine have been unsuccessful, probably because most were aimed at teaching the immune system to recognize and attack HIV circulating in the blood stream. Now that it is clear that the primary internal spread of the virus is directly from cell to cell, researchers can work on drugs that inhibit the formation of synapses by infected cells and their endocytosis by healthy ones. It also seems likely that HIV’s mechanism for infection will provide insight on the behaviors of viruses that cause other intractable diseases.

There’s still so much to learn about how life works, so much biology left to do – it’s exciting.