[Isoform 1]: Cell surface receptor that plays important roles in innate and adaptive immunity by amplifying inflammatory responses (PubMed:10799849, PubMed:21393102). Upon activation by various ligands such as PGLYRP1, HMGB1 or HSP70, multimerizes and forms a complex with transmembrane adapter TYROBP/DAP12 (PubMed:17568691, PubMed:25595774, PubMed:29568119). In turn, initiates a SYK-mediated cascade of tyrosine phosphorylation, activating multiple downstream mediators such as BTK, MAPK1, MAPK3 or phospholipase C-gamma (PubMed:14656437, PubMed:21659545). 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:17098818, PubMed:17568691). 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 (PubMed:11323674, PubMed:21393102). {ECO:0000269|PubMed:10799849, ECO:0000269|PubMed:11323674, ECO:0000269|PubMed:14656437, ECO:0000269|PubMed:17098818, ECO:0000269|PubMed:17568691, ECO:0000269|PubMed:21393102, ECO:0000269|PubMed:21659545, ECO:0000269|PubMed:25595774, ECO:0000269|PubMed:29568119}. [Isoform 2]: Acts as a decoy receptor, counterbalancing TREM1 pro-inflammatory activity through the neutralization of its ligand. . This is the function of Ensembl gene identifier ENSG00000124731 (TREM1, triggering receptor expressed on myeloid cells 1).