Abstract: Novel activating receptors of the Ig super-family expressed on human myeloid cells, called TREM(s) (triggering receptor expressed on myeloid cells) are provided. Specifically, two (2) members of TREMs, TREM-1 and TREM-2 are disclosed. TREM-1 is a transmembrane glycoprotein expressed selectively on blood neutrophils and a subset of monocytes but not on lymphocytes and other cell types and is upregulated by bacterial and fungal products. Use of TREM-1 in treatment and diagnosis of various inflammatory diseases is also provided. TREM-2 is also a transmembrane glycoprotein expressed selectively on mast cells and peripheral dendritic cells (DCs) but not on granulocytes or monocytes. DC stimulation via TREM-2 leads to DC maturation and resistance to apoptosis, and induces strong upregulation of CCR7 and subsequent chemotaxis toward macrophage inflammatory protein 3-?. TREM-2 has utility in modulating host immune responses in various immune disorders, including autoimmune diseases and allergic disorders.