Green tea has anti-HIV effect in test tube

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An ingredient in green tea may reduce HIV binding to human CD4 cells by approximately 40% within an hour of drinking two to three cups of green tea, according to a test tube study conducted at the University of Sheffield, England, published in the Journal of Allergy and Clinical Immunology. However further research will be needed to show whether drinking green tea protects against HIV infection or disease progression.

Green tea has long been promoted for its health-giving properties, and recent research has shown that it contains flavonoids with anti-bacterial, anti-tumour and anti-viral effects in the test tube. Several studies have now demonstrated that derivatives of a flavonoid in green tea can reduce HIV replication in the test tube, and that epigallocatechin gallate (EGCG), the main flavonoid in green tea, can occupy the CD4 receptor on CD4+ lymphocytes and prevent HIV’s gp120 protein from binding to the receptor.

The latest study, conducted by Professor Mike Williamson, from the Department of Molecular Biology and Biotechnology at the University of Sheffield, and colleagues from the Baylor College of Medicine in Texas, shows that EGCG can prevent HIV from binding to the CD4 receptor at levels that are "physiologically relevant" – that is, estimated to reflect the levels of the flavonoid that would be achieved after drinking a few cups of green tea.

Glossary

receptor

In cell biology, a structure on the surface of a cell (or inside a cell) that selectively receives and binds to a specific substance. There are many receptors. CD4 T cells are called that way because they have a protein called CD4 on their surface. Before entering (infecting) a CD4 T cell (that will become a “host” cell), HIV binds to the CD4 receptor and its coreceptor. 

gp120

A glycoprotein on the HIV envelope. gp120 binds to a CD4 receptor on a host cell, such as a CD4 T lymphocyte (CD4 cell). This starts the process by which HIV fuses its viral membrane with the host cell membrane and enters the host cell.

concentration (of a drug)

The level of a drug in the blood or other body fluid or tissue.

CD4 receptor

A molecule on the surface of some cells onto which HIV can bind. To enter a host cell, HIV binds to a CD4 receptor and a coreceptor (either CCR5 or CXCR4) on the host cell. CD4 receptors are found on CD4 cells, other types of T cells, macrophages, monocytes, and dendritic cells.

protein

A substance which forms the structure of most cells and enzymes.

The researchers incubated human CD4+ T-cells for one hour with differing concentrations of EGCG or a control catechin that does not bind to the CD4 receptor and then challenged with a recombinat form of the HIV-1 gp120 protein. The extent of gp120 was then analysed at each concentration.

Human serum was not found to affect EGCG binding to CD4 lymphocytes, nor the inhibitory effect of EGCG on gp120 binding.

At a concentration of 0.2µmol/L (the minimum concentration likely after ingesting green tea), EGCG reduced HIV binding by 40%, and the researchers calculated from inhibitory effects at other concentrations that two to three cups of green tea could be expected to reduce HIV binding by ten to twenty fold.

“Although we would not advocate green tea as the sole prophylactic, it may be useful in combination with other antiretroviral therapies,” the authors conclude.

However, the study cannot prove that green tea prevents HIV infection in humans, or slows the progression of HIV disease by reducing the effect of HIV on the CD4 cell population.

Dr Mike Williamson of Sheffield University said that further studies were planned with Baylor College in order to learn more about the clinical effects, using the purified flavonoid rather than green tea itself.

“It is not a cure, and nor is it a safe way to avoid infection, however, we suggest that it should be used in combination with conventional medicines to improve quality of life for those infected. Future research is also currently under way in order to determine how much effect can be expected from different amounts of tea.”

References

Williamson MP et al. Epigallocatechin gallate, the main polyphenol in green tea, binds to the T-cell receptor, CD4: potential for HIV-1 therapy. J Allergy Clin Immunol 118: 1369-74, 2006.

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