快猫短视频

HUMAN immune proteins that coat HIV may help transport the virus throughout
the body, a new study of infected patients suggests. The results add to fears
that some AIDS vaccines might promote rather than prevent infection.

Much of the research on HIV has focused on T cells. The virus grabs hold of a
protein on these cells called CD4 and uses it to break inside and start
replicating. But test tube experiments earlier this year by Susan Moir and her
colleagues at the National Institute of Allergy and Infectious Diseases near
Washington DC and other researchers suggested that B cells, which produce
antibodies, can also interact with the virus鈥攅ven though they lack
CD4.

To see if B cells actually harbour the virus during an infection, Moir鈥檚 team
has since examined 23 patients with high levels of virus in their blood. All had
virus closely associated with their B cells, and the researchers also found that
virus could pass from these cells to CD4-bearing T cells and trigger an
infection. But it turned out that the virus wasn鈥檛 replicating inside the B
cells. Instead it was attached to the outside, with the help of an immune
protein known as C3.

C3 is part of a system of interacting proteins called the complement cascade
that bind to microbes directly or, as is the case for HIV, through antibodies.
Normally, the complement attack ends up destroying the invader. But the new
results suggest that for HIV, the complement system simply acts as a travel
pass, allowing the virus to hop aboard B cells and look for CD4 cells to invade.
鈥淔or the virus, these cells are very nice carriers,鈥� says Moir. 鈥淭hey travel
through the blood and into tissues.鈥�

鈥淚t鈥檚 a very important result鈥攁 real paradigm shift,鈥� says immunologist
Greg Spear of Rush University in Chicago. He points out that complement proteins
bind to many types of cells, so HIV may be able to hitch a ride on nearly any
cell that passes by.

The results could also help explain why some antibodies seem to enhance
rather than prevent HIV infection. In the past year scientists searching for an
AIDS vaccine have become concerned that the wrong type of vaccine could promote
HIV infection through this mechanism, which has been dubbed 鈥渆nhancement鈥�
(快猫短视频, 27 May, p 17).

Moir thinks that boosting antibodies with a vaccine might trigger complement
binding to B cells, and hence help to spread HIV around the body. She says a
better understanding of complement鈥檚 role in HIV biology could help us to design
vaccines that trigger the most protective kind of antibody response.