How HIV disables the cells' call for help

July 07, 2005

The HIV virus hides out in the very immune system cells that are meant to protect the body from viral infection. But how does it prevent these cells from mounting a full-scale attack against the invader? In research published today in the Journal of Clinical Investigation, a team at the Weizmann Institute of Science has shown how a part of a protein on the virus' outer surface interferes with the cells' normal immune response. But their work may have wider implications: this molecular fragment, which has such a devastating effect in one disease, might turn out to be an effective treatment for other disorders such as rheumatoid arthritis.

In the initial stages of HIV infection, the protein coatings of the viruses fuse with the outer membranes of T cells - immune system cells that recognize foreign invaders and alert other types of immune cell to come to the rescue. The genetic material of the virus, which is basically a strand of RNA, then forces the cell's DNA to make copies of it. Newly minted viruses created by the host DNA later break out of the cell membrane to infect other cells. Many believed that the very act of breaking into T cells and hijacking their DNA was enough to destroy the ability of these cells to call up immune support.

But Institute scientists Prof. Yechiel Shai of the Biological Chemistry Department, Prof. Irun Cohen of the Immunology Department and graduate students Francisco Quintana and Doron Gerber thought there must be more to the story. T cells identify invaders using receptors, like security antennae, on their outer walls. A virus, especially one with its own surface equipment for seeking out specific T cells, would be hard-pressed to slip past these receptors without raising the alarm. The scientists surmised that the virus must be able to actively disable some part of the immune cell's system.

They investigated a peptide fragment called FP (fusion peptide), a segment of the HIV protein gp41 found on the viral envelop. FP was known to play a role in the complex process in which the viral envelop fuses with the cell membrane in the initial stage of cell infection. The researchers suspected that FP, which is only exposed for a short period during this process, may have enough time to affect the immune response as well. Indeed, they found that FP locks on to several proteins on the cell walls that are involved in invoking a large-scale immune response, effectively shutting them down.

From their new understanding of how a tiny virus can gain control of the body's immune response, the scientists made an intuitive leap. In autoimmune diseases, the same T cells that play host to HIV viruses are overactive, mistakenly attacking the body's cells instead of foreign invaders. If the viruses use FPs to override the cells' call for help, could their actions, which block one type of immune response without killing the cell, be applied to these autoimmune diseases? To check their theory, the research team tested FP on rats suffering from an autoimmune syndrome similar to human rheumatoid arthritis, and on cultured human T cells. As they predicted, the rats treated with FP showed a significant reduction in joint swelling and other symptoms of arthritis.

Shai points out that using FP, a tiny piece of a piece of the HIV virus, would pose no danger to patients as it lacks any ability to either infect cells or to reproduce. Rather, as the scientists note in their paper, the study of a destructive virus may contain important lessons on how to regulate the immune system. "Perhaps," says Cohen, "we humans can adopt the virus peptide to better control overactive autoimmunity."

Prof. Irun Cohen's research is supported by the Minna James Heineman Stiftung; the Robert Koch Minerva Center for Research in Autoimmune Disease; and Mr. and Mrs. Samuel Theodore Cohen, Chicago, IL.

Prof. Cohen is the incumbent of the Helen and Morris Mauerberger Professorial Chair in Immunology.

Prof. Yechiel Shai's research is supported by Robert Koch Minerva Center for Research in Autoimmune Disease; and the estate of Julius and Hanna Rosen.

Prof. Shai is the incumbent of the Harold S. and Harriet B. Brady Professorial Chair in Cancer Research.
-end-
The Weizmann Institute of Science in Rehovot, Israel, is one of the world's top-ranking multidisciplinary research institutions. Noted for its wide-ranging exploration of the natural and exact sciences, the Institute is home to 2,500 scientists, students, technicians and supporting staff. Institute research efforts include the search for new ways of fighting disease and hunger, examining leading questions in mathematics and computer science, probing the physics of matter and the universe, creating novel materials and developing new strategies for protecting the environment.

American Committee for the Weizmann Institute of Science

Related Immune System Articles from Brightsurf:

How the immune system remembers viruses
For a person to acquire immunity to a disease, T cells must develop into memory cells after contact with the pathogen.

How does the immune system develop in the first days of life?
Researchers highlight the anti-inflammatory response taking place after birth and designed to shield the newborn from infection.

Memory training for the immune system
The immune system will memorize the pathogen after an infection and can therefore react promptly after reinfection with the same pathogen.

Immune system may have another job -- combatting depression
An inflammatory autoimmune response within the central nervous system similar to one linked to neurodegenerative diseases such as multiple sclerosis (MS) has also been found in the spinal fluid of healthy people, according to a new Yale-led study comparing immune system cells in the spinal fluid of MS patients and healthy subjects.

COVID-19: Immune system derails
Contrary to what has been generally assumed so far, a severe course of COVID-19 does not solely result in a strong immune reaction - rather, the immune response is caught in a continuous loop of activation and inhibition.

Immune cell steroids help tumours suppress the immune system, offering new drug targets
Tumours found to evade the immune system by telling immune cells to produce immunosuppressive steroids.

Immune system -- Knocked off balance
Instead of protecting us, the immune system can sometimes go awry, as in the case of autoimmune diseases and allergies.

Too much salt weakens the immune system
A high-salt diet is not only bad for one's blood pressure, but also for the immune system.

Parkinson's and the immune system
Mutations in the Parkin gene are a common cause of hereditary forms of Parkinson's disease.

How an immune system regulator shifts the balance of immune cells
Researchers have provided new insight on the role of cyclic AMP (cAMP) in regulating the immune response.

Read More: Immune System News and Immune System Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.