Gli scienziati scoprono 'barriera naturale' contro
l'HIVSOURCES:
- Teunis Geijtenbeek, Ph.D., department of molecular cell biology
and immunology, Vrije University Medical Center, Amsterdam, The Netherlands;
Jeffrey Laurence, M.D., professor, medicine and director, Laboratory for AIDS
Virus Research, Weill Cornell Medical College, New York City; Nature Medicine
online
- Foundation for AIDS Research.
(HealthDay) - I
ricercatori hanno scoperto che le cellule della mucosa del prepuzio,
facente parte degli organi genitali maschili, sono in grado di produrre una
proteina che "mangia" e distrugge il virus dell’HIV - impedendone la diffusione
nell’organismo e possibilmente tenendo la diffusione dell’AIDS nel partner più
contenuta di quanto potrebbe essere altrimenti.
Ancora più
importante, migliorando le funzioni e l’attività di difesa di questa proteina,
chiamata ”Langerin“, si potrebbe creare un nuovo potente strumento per limitare
la trasmissione del virus che causa l'AIDS, hanno aggiunto gli scienziati
olandesi.
Langerin is produced by Langerhans cells, which form a web-like
network in skin and mucosa. This network is one of the first structures HIV
confronts as it attempts to infect its host.
Un ricercatore immunologo
presso il Vrije University Medical Center di Amsterdam, Teunis Geijtenbeek, ha
detto che tale proteina è in grado di eliminare ogni virus proveniente
dall’esterno dell’organismo, in modo da prevenire eventuali
infezioni.
"And since generally all tissues on the outside of our
bodies have Langerhans cells, we think that the human body is equipped with an
antiviral defense mechanism, destroying incoming viruses," Geijtenbeek
said.
The finding, reported in the March 4 online issue of Nature
Medicine, "is very interesting and unexpected," said Dr. Jeffrey Laurence,
director of the Laboratory for AIDS Virus Research at the Weill Cornell Medical
College, in New York City. "It may explain part of the relative inefficiency of
HIV in being transmitted."
Even though HIV has killed an estimated 22
million people since it was first recognized more than 25 years ago, it is
actually not very good at infecting humans, relatively speaking.
For example,
the human papillomavirus (HPV), which causes cervical cancer, is nearly 100
percent infectious, Laurence noted. That means that every encounter with the
sexually transmitted virus will end in infection.
"On the other hand,
during one episode of penile-vaginal intercourse with an HIV-infected partner,
the chance that you are going to get HIV is somewhere between one in 100 and one
in 200," Laurence said.
Experts have long puzzled why HIV is relatively
tough to contract, compared to other pathogens. The Dutch study, conducted in
the laboratory using Langerhans cells from 13 human donors, may explain
why.
When HIV comes in contact with genital mucosa, its ultimate target
-- the cells it seeks to hijack and destroy -- are immune system T-cells. But
T-cells are relatively far away (in lymph tissues), so HIV uses nearby
Langerhans cells as "vehicles" to migrate to T-cells.
For decades, the
common wisdom was that HIV easily enters and infects Langerhans cells.
Geijtenbeek's team has now cast doubt on that notion.
Looking closely at the
interaction of HIV and Langerhans cells, they found that the cells "do not
become infected by HIV-1, because the cells have the protein Langerin on their
cell surface," Geijtenbeek said. "Langerin captures HIV-1 very efficiently, and
this Langerin-bound HIV-1 is taken up (a bit like eating) by the Langerhans
cells and destroyed."
In essence, Geijtenbeek said, "Langerhans cells act
more like a virus vacuum cleaner."
Only in certain circumstances -- such as
when levels of invading HIV are very high, or if Langerin activity is
particularly weak -- are Langerhans cells overwhelmed by the virus and
infected.
The finding is exciting for many reasons, not the least of which is
its potential for HIV prevention, Geijtenbeek said.
"We are currently
investigating whether we can enhance Langerin function by increasing the amount
of Langerin on the cell surface of Langerhans cells," he said. "This might be a
real possibility, but it will take time. I am also confident that other
researchers will now also start exploring this possibility."
The
discovery might also help explain differences in vulnerability to HIV infection
among people.
"It is known that the Langerin gene is different in some
individuals," Geijtenbeek noted. "These differences could affect the function of
Langerin. Thus, Langerhans cells with a less functional Langerin might be more
susceptible to HIV-1, and these individuals are more prone to infection. We are
currently investigating this."
The finding should also impact the race to
find topical microbicides that might protect women against HIV infection.
Choosing compounds that allow Langerin to continue to work its magic will
enhance any candidate microbicide's effectiveness, the Dutch researcher
said.
Laurence did offer one note of caution, however.
"In the test tube,
this is a very important finding," he said. "But there are many things in the
test tube that don't occur when you get into an animal or a human. Having said
that, though, this is a very intriguing finding."
FONTE: http://news.healingwell.com/index.php?p=news1&id=602421