Researchers at Washington University of Medicine in St. Louis found that mice that lacked the B-cells and the antibodies they produce could not fight off the virus. The mice developed fatal brain and spinal cord infections. Their report appears in the February issue of the Journal of Virology.
The researchers first infected mice that lacked T-cells and B-cells -- two important immune system components -- and compared their response to mice with normal immune systems.
T-cells coordinate immune system responses and kill infected cells, while B-cells produce antibodies that attack viruses before they can infect cells.
Even with low does of the West Nile virus, the immune-deficient mice got sick and died. However, the researchers found the immune-deficient mice could resist the virus if they were given a dose of B-cells after being injected with the West Nile virus.
To confirm the critical role of B-cells and their antibodies, the researchers injected the West Nile virus into mice who lacked B-cells but had T-cells. The mice became sick and died.
The findings suggest humans who have weak antibody responses in the early stages of West Nile virus infection are more likely to develop serious disease.
Last year, doctors in the United States reported more than 3,500 cases of West Nile virus infection in humans, with 5 percent to 10 per cent of those resulting in serious illness or death.
Here's where you can learn more about West Nile virus.