BBC News - July 14, 2009

Experts believe women are naturally programmed to be the weaker sex when it comes to fighting off HIV.

It is well known that HIV progresses faster in women than in men with similar levels of HIV in the blood.

Now a US research team has found that a receptor molecule involved in the first-line recognition of HIV responds differently in women.

The findings in Nature Medicine might provide new ways to treat HIV and slow or stop the progression to Aids.

The Massachusetts General Hospital team explored whether known gender differences in the immune system might explain why HIV progresses faster in women.

They focused on immune cells called plasmacytoid dendritic cells or pDCs which are among the first cells to recognise and fight HIV.

Lab studies showed that a higher percentage of these cells from healthy, uninfected women became activated when presented with HIV-1 as compared with pDCs from healthy men.

Next they studied whether a woman's hormone levels might be involved.

Hormonal link

They found that pDCs from older women who had gone through the menopause had similar activity to that observed in men.

But premenopausal women with higher levels of the hormone progesterone had increased activation of pDCs in response to HIV-1.

Armed with this knowledge they then tested whether this increased activation of pDCs, in turn, led to activation of other immune cells called T cells.

Question: " Whilst there are some genetic differences based on sex, access to treatment remains the single most important factor in preventing HIV from progressing to Aids " -- Jo Robinson from Terrence Higgins Trust

When they tested the blood of men and women with HIV-1 they found the women did have higher levels of activated CD8-positive T cells than men with identical blood levels of HIV-1.

Lead researcher Dr Marcus Altfeld said: "While stronger activation of the immune system might be beneficial in the early stages of infection, resulting in lower levels of HIV-1 replication, persistent viral replication and stronger chronic immune activation can lead to the faster progression of Aids that has been seen in women."

Ultimately, drugs that work to modify this pathway might help patients with HIV, he said.

His team is beginning preliminary laboratory studies into this.

Jo Robinson from Terrence Higgins Trust said: "This is an interesting piece of research exploring whether HIV progresses faster in women than in men.

"Whilst there are some genetic differences based on sex, access to treatment remains the single most important factor in preventing HIV from progressing to Aids.

"Unfortunately women are most likely to be affected by the virus in places like sub-Saharan Africa, where they are also least likely to be able to access HIV treatment."

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