TYRO3 blocking peptide

Many receptors that are employed for the engulfment of apoptotic cells are also used for the recognition and phagocytosis of bacteria. Tyro3, Axl, and Mertk (TAM) are important in the phagocytosis of apoptotic cells by macrophages. Animals lacking these receptors are hypersensitive to bacterial products. In this report, we examine whether the TAM receptors are involved in the phagocytosis of bacteria. We found that macrophages lacking Mertk, Axl, Tyro3 or all three receptors were equally efficient in the phagocytosis of Gram-negative E. coli. Similarly, the phagocytosis of E. coli and Gram-positive S. aureus bioparticles by macrophages lacking TAM receptors was equal to wild-type. In addition, we found that Mertk did not play a role in killing of extracellular E. coli or the replication status of intracellular Francisella tularensis. Thus, while TAM receptors may regulate signal transduction to bacterial components, they are not essential for the phagocytosis and killing of bacteria. (C) 2009 Elsevier Inc. All rights reserved.

Protein S (ProS) and growth arrest-specific 6 (Gas6) bind to phosphatidylserine (PtdSer) and induce efferocytosis upon binding TAM-family receptors (Tyro3, Axl, and Mer). Here, we produced mouse ProS, Gas6, and TAM-receptor extracellular region fused to IgGfragment crystallizable region in HEK293T cells. ProS and Gas6 bound Ca2+ dependently to PtdSer (K-d 20-40 nM), Mer, and Tyro3 (K-d 15-50 nM). Gas6 bound Axl strongly (K-d < 1.0 nM), but ProS did not bind Axl. Using NIH 3T3-based cell lines expressing a single TAM receptor, we showed that TAM-mediated efferocytosis was determined by the receptor-binding ability of ProS and Gas6. Tim4 is a membrane protein that strongly binds PtdSer. Tim4 alone did not support efferocytosis, but enhanced TAM-dependent efferocytosis. Resident peritoneal macrophages, Kupffer cells, and CD169(+) skin macrophages required Tim4 for TAM-stimulated efferocytosis, whereas efferocytosis by thioglycollate-elicited peritoneal macrophages or primary cultured microglia was TAM dependent, but not Tim4 dependent. These results indicate that TAM and Tim4 collaborate for efficient efferocytosis in certain macrophage populations.