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Monday, September 8, 2008

How malaria parasites attack blood cells

How malaria parasites attack blood cells

MIT zooms in on malaria-infected cells Work could aid in diagnostics, drug testing

The study establishes the first experimental connection between cell membrane vibration and the pathological state of a living cell.

"You can establish a measurement of membrane-fluctuation changes as a function of the gradual progression from a healthy state to a severely pathological state," said Suresh, who has appointments in materials science and engineering, biological engineering, mechanical engineering and the Harvard-MIT Division of Health Sciences and Technology.

It has been known for more than a century that red blood cell membranes continuously undulate. These vibrations are difficult to study because the measurements involved are so tiny (nanometer, or billionth of a meter, scale), and occur in just microseconds.

Suresh and colleagues have previously shown that the cell membranes of red blood cells invaded by the malaria parasite lose their elasticity, as proteins transported from the parasite attach to the membranes and make them significantly stiffer.

In the new paper, the researchers describe using a technique called diffraction phase microscopy to image living cells over the first 48 hours of malaria parasite maturation inside the cell. They showed that infection reduces elasticity and decreases the vibration frequency of the cell membrane.

The team also used a technique called tomographic phase microscopy, which was developed in Feld's laboratory and is based on the same concept as a CT scan: To create a 3D image, the researchers combine about 100 two-dimensional images taken from different angles. Those images are produced with a technique known as interferometry, in which a light wave passing through a cell is compared with a reference wave that doesn't pass through it.

The technique allowed them to study changes in the refractive index of a cell, which is a measure of how much the speed of light is reduced as it passes through the material.

Images generated by tomographic phase microscopy revealed the degradation of hemoglobin as the malaria parasite interacted with the cell.

In the future, the microscopy technology could be used to develop a diagnostic tool that would detect malaria or other human diseases by measuring cell membrane properties. It could also be used to test the efficacy of potential drugs.

The current project got underway about two years ago, after Suresh gave a talk at the Spectroscopy Laboratory on his work studying the mechanical stiffness of malaria-infected red blood cells. Feld and his colleagues were already working on microscopy techniques to visualize red blood cells, so the groups decided to collaborate.

Healthy RBC exhibits a characteristic biconcave shape (left). During the early stage of parasite maturation (center), the parasitophorus vacuole is shown as yellow region. In the late schizont stage, parasitized RBC is subjected to severe morphological changes (right). The blue regions inside the cell indicate parasite-produced hemozoin, a crystallized form of digested hemoglobin.



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