How Does the Hypothalamus "Know" to Raise the Body's Temperature

How does the hypothalamus "know" to raise the body's temperature set point to produce a fever?

A) Infected blood passes over the temperature-sensing nerve cells in the brain, and when those cells fire more slowly, the hypothalamus raises the body's temperature set point.
B) The infecting pathogen interferes with the normal temperature set point, so it changes.
C) In response to an infection, a particular chemical signal binds to the hypothalamus, raising the set point temperature.
D) You shiver.
E) The immune system bypasses the hypothalamus to raise the body's temperature.