HIV infection mystery solved

By R. Prasad

CHENNAI MAY 1. Scientists have finally solved a longstanding scientific mystery — how Human Immunodeficiency Virus (HIV) manages to infect, multiply with abandon and eventually subvert the human immune system to cause AIDS.

Thomas Hope and David McDonald, microbiologists at the University of Illinois at Chicago, found that in the early stages of infection, the dendritic cells (Langerhans cells) — the first line of defence for the body — gets infected. The fact that the HIV first infects the dendritic cells before it attacks the T cells was known long ago. But what was not known was how the virus manages to gain entry into the T cells of the immune system.

These scientists have now discovered how this is done and their results were published today in the online version of the journal, Science.

Dendritic cells or Langerhan cells are the watchdogs of the immune system. They patrol and normally attack and degrade any virus or pathogen, which enters the body, into tiny bits. These tiny bits are then presented as antigens to T cells to prepare in advance the immune system for any possible attack by a foreign body.

Dendritic cells present the antigen to the T cells by making a physical contact in the form of a tight interface called an immunological synapse. This contact helps cells to talk to one another via molecular signals. Once the communication is done, the T cells are alerted and it responds to spot and destroy the virus.

However, the hitch with the HIV is that the dendritic cells or Langerhans cells are unable to destroy all the HIV before presenting them as antigens to the T cells.

Scientists have now discovered live dendritic cells with the HIV particles inside them.

And, as the dendritic cells make contact with the T cells for alerting them, the HIV particles take advantage of the contact and move into the T cells.

Just as dendritic cells could signal the start of the immune response to the HIV, the immunological synapse (the contact) helps jump-start infection.

In short, the HIV exploits the dendritic machinery for its own ends, taking advantage of the cells' special relationship with the T cells to gain entry and launch its assault.

In the process, the HIV does not get destroyed. Once inside the T cells, the HIV multiplies and slowly kills the T cells. With time, the person progresses to a diseased state (AIDS).

Recent studies have shown that the Ebola virus, cytomegalovirus, and the bacterium that causes tuberculosis follow the same modus operandi. as the HIV.

It is hoped that the discovery will open up new avenues in the fight against prevention of the HIV infection.<137>