The Dendritic Cell Receptor Clec9A Binds Damaged Cells via Exposed Actin Filaments

Abstract

The immune system must distinguish viable cells from cells damaged by physical and infective processes. The damaged cell-recognition molecule Clec9A is expressed on the surface of the mouse and human dendritic cell subsets specialized for the uptake and processing of material from dead cells. Clec9A recognizes a conserved component within nucleated and nonnucleated cells, exposed when cell membranes are damaged. We have identified this Clec9A ligand as a filamentous form of actin in association with particular actin-binding domains of cytoskeletal proteins. We have determined the crystal structure of the human CLEC9A C-type lectin domain and propose a functional dimeric structure with conserved tryptophans in the ligand recognition site. Mutation of these residues ablated CLEC9A binding to damaged cells and to the isolated ligand complexes. We propose that Clec9A provides targeted recruitment of the adaptive immune system during infection and can also be utilized to enhance immune responses generated by vaccines.

Intracellular metabolite β-glucosylceramide is an endogenous Mincle ligand possessing immunostimulatory activity

“…However, the exact contribution of SAP-130 as a damageassociated molecular pattern cannot be addressed by conventional genetic approaches, as this protein is essential for RNA splicing, a fundamental process in all living cells. For the same reason, the precise contribution of F-actin as a Clec9a ligand (49,50) is difficult to prove by gene-deletion approaches, because actin is an indispensable cytoskeletal protein. Some other CLRs recognize crystallized self-components that do not exist under normal conditions (51,52).…”

Keratin mediates the recognition of apoptotic and necrotic cells through dendritic cell receptor DEC205/CD205

“…Compared with other receptors such as CLEC9A (13,15), PtdSerR (12), and TIM family members (16), the DEC205-keratin interaction represents a different pathway for dead cell recognition and clearance (Fig. 5H).…”

“…Dead cells are recognized and engulfed by phagocytes through their cell surface receptors (4), leading to either immune activation or tolerance (5)(6)(7)(8). A number of receptors have been found to be able to mediate the clearance of dead cells (3); for example, CD14 (9), CD36 (10), integrin (11), PtdSerR (12), CLEC9A (13)(14)(15), and TIM receptor family members (16). Among known dead cell markers, phosphatidylserine (PS) is the most common one that can be recognized by several receptors such as CD36, PtdSerR, and TIM receptors, and acts as an "eatme" signal for phagocytes mediating dead cell clearance (4).…”

“…Other than PS, several cellular proteins have also been found to be able to perform the similar function. For example, actin filaments can be recognized by CLEC9A as a damaged cell marker (13,15). The recognition of different dead cell markers by phagocytes provides an efficient way to remove cell debris completely.…”

The Mononuclear Phagocyte System in Homeostasis and Disease: A Role for Heme Oxygenase-1

“…First, CD8 + splenic DC [and, presumably, their peripheral equivalents (23,47)] express SRs [CD36 (26), DEC 205 (92,93), and Clec9A (195)] that are necessary for the recognition, phagocytic clearance, and tolerant response to self-moieties that originate from apoptotic, necrotic, or senescent cells during homeostasis and tissue …”