NRP1 and fibrosarcoma: TREM-1 is a transmembrane receptor featuring an extracellular immunoglobulin domain, a transmembrane region, and a short cytoplasmic tail lacking intrinsic signaling motifs (11, 37), was initially identified in peripheral monocytes and neutrophils, with subsequent detection in macrophages, endothelial cells, and fibrosarcoma cell lines (38).