Fever is a NON-SPECIFIC immune response, called a "constitutional symptom," because varies entities may initiate a pyrogenic (fever) response. Bacterial infection, Viral infection, inflammation, and auto-immune reactions can all cause a fever at some point of their processes.
Sensory receptors?? I believe that is the answer but you may have wanted a more in depth explanation, if so, my bad.
Protein, the building blocks of proteins are amino acids, different sequences and combinations of these amino acids result in huge numbers of proteins which have a variety of functions.
