MSR1, as known as macrophage scavenger receptor types I and II isoform type 1, is single-pass type II membrane protein. Scavenger receptors are a group of membrane receptors that recognize and internalize modified low density lipoproteins (LDLs) and participate in the removal of many foreign substances and waste materials in the living body. Scavenger receptors are categorized into three classes, and class A mainly expressed in macrophage includes three isoforms derived by alternative splicing. This protein, has been suggested to play important roles in macrophage growth, cell adhesion, osteoclast differentiation, and as well as intracellular signaling.