A vaccine used to immunize laboratory mice against an Alzheimer's disease-like condition also caused their brains to bleed and increased their risk of strokes, according to researchers at the University of Basel in Switzerland.

This finding is being linked to the study of an experimental human vaccine that caused cerebral inflammation, causing the trial to be halted earlier in 2002. Researchers believe the bleeding in the mice and the inflammation in humans may be from the effects of the immunizations on damaged blood vessels.

Researchers injected elderly mice with antibodies against amyloid, the protein that causes the plaques found in the brains of Alzheimer's patients. After five months, the mice had smaller deposits of amyloid in their brains, but they also had small hemorrhages in the brain's blood vessels. Investigators speculate that clearing out amyloid might actually weaken the blood vessels.

The results suggest that immunizations against Alzheimer's disease may be more suited to protecting healthy brains than repairing diseased ones. It may also be necessary to screen patients for blood vessel weakness before immunizations.

Some researchers do not believe the bleeding in the mice is related to the inflammation found in humans because this is only the first time bleeding has been seen in any animal or human study of Alzheimer's vaccines.

Other sources: Nature Science Update