The disease attacks immune cells called granulocytes, which the body normally uses to destroy infectious pathogens.
In the current study, Rikihisa and her colleagues studied two groups of mice. Animals in one group lacked a protein important for maintaining normal blood cholesterol levels, while mice in the other group had this protein, called apoliprotein E (apoE).
For about a month several mice from each group ate a diet high in cholesterol, while the rest of the animals ate a diet with normal cholesterol levels. At the end of the month, some of the mice from each feeding group were infected with A. phagocytophilum.
Ten days after infecting the mice, the researchers collected blood samples from each mouse and also harvested each animal's spleen and liver. They determined the extent of the infection based on the amount of bacteria found in each tissue. Since the spleen and liver both filter blood, and the liver makes and stores cholesterol, the researchers thought that they may find higher concentrations of bacteria in these organs.
A. phagocytophilum levels were 10 times higher in mice predisposed to high blood cholesterol levels and that ate the high-cholesterol diet than in any other group of mice, including the animals that were predisposed and ate a normal-cholesterol diet.
Bacterium levels were highest in the blood and the spleen, and were quite low in the liver of any of the mice.
Cholesterol levels increased four times in the mice that ate the high-cholesterol diet and that were predisposed to high cholesterol. Yet cholesterol levels remained normal in the mice which had the cholesterol predisposition but consumed the normal-cholesterol diet.
Some people have mutations in the apoE gene, which controls apoE production. As a result, they cannot adequately maintain blood cholesterol. In humans, this mutation can cause blood cholesterol levels to signific
Contact: Yasuko Rikihisa
Ohio State University