In response to inflammation and infection stimuli, macrophages express different pattern recognition receptors (PRRs), including surface receptors such as toll-like receptors (TLRs), and trigger receptors expressed on myeloid cells 1 (TREM-1) and cytosolic receptors such as Nod-like receptors (NLRs), which may work in concert to activate common downstream innate signaling cascades comprised of MAP kinases and transcription factors [29]. Here, TREM1 is linked to infection.