Immune Sensing of Cell Death through Recognition of Histone Sequences by C-Type Lectin-Receptor-2d Causes Inflammation and Tissue Injury

Abstract

The immune system monitors the health of cells and is stimulated by necrosis. Here we examined the receptors and ligands driving this response. In a targeted screen of C-type lectin receptors, a Clec2d reporter responded to lysates from necrotic cells. Biochemical purification identified histones, both free and bound to nucleosomes or neutrophil extracellular traps, as Clec2d ligands. Clec2d recognized poly-basic sequences in histone tails and this recognition was sensitive to post-translational modifications of these sequences. As compared with WT mice, Clec2d À/À mice exhibited reduced proinflammatory responses to injected histones, and less tissue damage and improved survival in a hepatotoxic injury model. In macrophages, Clec2d localized to the plasma membrane and endosomes. Histone binding to Clec2d did not stimulate kinase activation or cytokine production. Rather, histone-bound DNA stimulated endosomal Tlr9-dependent responses in a Clec2ddependent manner. Thus, Clec2d binds to histones released upon necrotic cell death, with functional consequences to inflammation and tissue damage.

Myeloid cells in sensing of tissue damage

“…In fact, this mechanism driven by HMGB1 has been proposed to play a role in the severe pulmonary inflammation occurring at late stages of COVID-19 [ 55 ]. In a similar way, histones released upon cell death are recognized by the CLR CLEC2D, transferring them to endosomal compartments where histones-bound DNA triggers TLR9-mediated inflammatory responses [ 56 •• ].…”

On Neutrophil Extracellular Trap (NET) Removal: What We Know Thus Far and Why So Little

“…Only a handful of empirical studies have reported on the mechanisms of NET removal. In the majority of them, the process was studied in vitro / ex vivo on isolated cells ( Supplementary Table S1 and Figure 3 ) [ 74 , 75 , 76 , 77 , 78 , 79 , 80 , 81 , 82 ]. Regrettably, only a couple of papers presented in vivo data [ 35 , 62 ].…”

“…What is more, proteomic analyses of NETs formed in response to PMA identified higher content of histone H2A and histone H3.1, whereas histone one family protein concentrations (H1.0, H1.4, and H1.5) are significantly higher in A23187-induced NETs [ 107 ]. In fact, two very recent publications report on a critical role of the histone component of NETs in their recognition as well as on involved receptors [ 81 , 82 ], issues discussed in the following paragraph.…”

“…The only two thus far identified receptors were shown to recognize histones, although none of the studies were directly aimed to investigate mechanisms of NET removal. Firstly, Lai et al [ 81 ] identified Clec2d, a C-type lectin receptor, as a histone sensing DAMP receptor ( Figure 3 H). All five types of histones (H1, H2A, H2B, H3 and H4) turned out to be the ligands for Clec2d, with the protein sequences in N-terminal (H1–H4) and C-terminal (H1) tail regions being primarily recognized.…”

“…All five types of histones (H1, H2A, H2B, H3 and H4) turned out to be the ligands for Clec2d, with the protein sequences in N-terminal (H1–H4) and C-terminal (H1) tail regions being primarily recognized. What is more, the positively charged residues on histone tails, especially on lysines, turned out to be of great importance, since removing the positive charge destroyed the stimulatory effect of histones [ 81 ]. The receptor is expressed on the plasma membrane as well as in intracellular vesicles, which colocalize with Rab7, a late endosomal protein, but not Eea1, an early endosomal protein.…”