Scientists in the US have created a chip that allows rapid detection of HIV infected cells in blood.

Monitoring HIV infected species involves counting a specific white blood cell population known as CD4+ T lymphocytes. People who suffer from the virus are advised to have regular checks on their CD4 count, and this is used to establish when antiretroviral drugs are needed. Clinically, if a person has a CD4 count below 200 cells per microlitre, they are diagnosed with AIDS and are prescribed antiretroviral treatment.

However, appropriate monitoring tools to determine CD4 counts are not widely available, particularly in developing countries. Mehmet Toner and colleagues from the Harvard Medical School, Boston, set out to find a cheaper and more practical CD4 counting device and came up with the idea of using a small chip.

The device works by injecting a finger prick of blood on the glass slide of the chip. The chip then selectively captures CD4 lymphocyte cells. After rinsing off the unbound cells, a simple light microscope is used to count the CD4 lymphocyte cells bound to the chip. 'This creates a low cost, rapid CD4 cell counting system appropriate for use in resource-limited settings,' said Toner. The team compared CD4 counts using their chip to standard flow cytometric measurements and discovered that the new chip produced very accurate counts.

According to Toner, the chip represents the first practical application of microfluidics in blood cell diagnostics. The team believe their work will fuel new research into microfluidic technology in the future. 'CD4 counting is just one application for devices of this type,' said Toner. This technique could be applied to a number of applications where specific and efficient cell isolation is required, he said.

Jenna Wilson