Cell surface receptor that plays important roles in innate and adaptive immunity by amplifying inflammatory responses. Upon activation by various ligands such as PGLYRP1, HMGB1 or HSP70, multimerizes and forms a complex with transmembrane adapter TYROBP/DAP12. In turn, initiates a SYK-mediated cascade of tyrosine phosphorylation, activating multiple downstream mediators such as BTK, MAPK1, MAPK3 or phospholipase C-gamma. This cascade promotes the neutrophil- and macrophage-mediated release of pro-inflammatory cytokines and/or chemokines, as well as their migration and thereby amplifies inflammatory responses that are triggered by bacterial and fungal infections (PubMed:23241959, PubMed:27328755). By also promoting the amplification of inflammatory signals that are initially triggered by Toll-like receptor (TLR) and NOD-like receptor engagement, plays a major role in the pathophysiology of acute and chronic inflammatory diseases of different etiologies including septic shock and atherosclerosis (By similarity). Monomer (PubMed:15561137). Homomultimer; when activated. Interacts with TYROBP/DAP12. Interacts with TLR4 (By similarity). Recruited to lipid rafts when activated. Deletion mutants do not show any influence of the antiviral T-cell response. However, TREM1 deficiency impairs secretion of CCL2 and TNF-alpha by neutrophils in response to viruses (PubMed:27328755). TREM-1/3-deficient animals have decreased neutrophils in the airway and these neutrophils have a defect in transepithelial migration (PubMed:23241959).