MARCO (macrophage receptor with collagenous structure) is an 80 kDa type II transmembrane glycoprotein that belongs to the class A scavenger receptor family. Mouse MARCO consists of a 48 amino acid (aa) cytoplasmic domain, a 21 aa transmembrane segment, and a 449 aa extracellular domain (ECD) that includes a stalk region, a collagenlike region, and one SRCR domain. MARCO is constitutively expressed on the surface of splenic and lymph node macrophages. MARCO binds LPS, lipoteichoic acid, and other determinants on Gram positive and Gram negative bacteria. It also binds modified LDL, CpG oligonucleotides, UGRP1, silica, and TiO2.