The correct option is C Pyrogen
Pyrogens can be the so called endotoxins or lipopolysaccharides, cell wall components of Gram negative bacteria such as E. coli, Salmonella or Bordetella, but also of the cell walls from Gram positive bacteria, e.g., so called lipoteichoic acids (LTA). When bacteria or viruses invade the body and cause tissue injury, one of the immune systems responses is to produce pyrogens. These chemicals are carried by the blood to the brain, where they disturb the functioning of the hypothalamus, the part of the brain, that regulates body temperature.