I've always thought that when I get a fever, it's my body trying to make things uncomfortable for the invading pathogen. And that's often true - higher temperatures can inhibit the bad guys' ability to replicate. But my fever may actually be a one-two-punch. In addition to slowing down the invader, the heat helps the immune system recruit more troops for a counter-attack. That finding appears in the Journal of Leukocyte Biology. Researchers warmed up one group of mice to body temperatures of about 103 degrees Fahrenheit. They left another group at normal core temperature - about the same as ours. Then they injected both groups of mice with an antigen, a substance that attracts the attention of the immune system. Blood samples taken three days later revealed that the feverish mice had nearly twice as many killer T cells: the kind of immune cells that can hunt down infected cells or tumor cells, and slaughter them. So when you're sick and you get the chills, the authors say, your body may be trying to tell you to hop under some blankets. Lie down, warm up and send a message. The heat is on.