TIM1 is an endogenous ligand for LMIR5/CD300b: LMIR5 deficiency ameliorates mouse kidney ischemia/reperfusion injury

Abstract

Leukocyte mono-immunoglobulin (Ig)–like receptor 5 (LMIR5)/CD300b is a DAP12-coupled activating receptor predominantly expressed in myeloid cells. The ligands for LMIR have not been reported. We have identified T cell Ig mucin 1 (TIM1) as a possible ligand for LMIR5 by retrovirus-mediated expression cloning. TIM1 interacted only with LMIR5 among the LMIR family, whereas LMIR5 interacted with TIM4 as well as TIM1. The Ig-like domain of LMIR5 bound to TIM1 in the vicinity of the phosphatidylserine (PS)-binding site within the Ig-like domain of TIM1. Unlike its binding to TIM1 or TIM4, LMIR5 failed to bind to PS. LMIR5 binding did not affect TIM1- or TIM4-mediated phagocytosis of apoptotic cells, and stimulation with TIM1 or TIM4 induced LMIR5-mediated activation of mast cells. Notably, LMIR5 deficiency suppressed TIM1-Fc–induced recruitment of neutrophils in the dorsal air pouch, and LMIR5 deficiency attenuated neutrophil accumulation in a model of ischemia/reperfusion injury in the kidneys in which TIM1 expression is up-regulated. In that model, LMIR5 deficiency resulted in ameliorated tubular necrosis and cast formation in the acute phase. Collectively, our results indicate that TIM1 is an endogenous ligand for LMIR5 and that the TIM1–LMIR5 interaction plays a physiological role in immune regulation by myeloid cells.

CD300b regulates the phagocytosis of apoptotic cells via phosphatidylserine recognition

“…These findings suggest that the binding of CD300b to TIM1-or TIM4-expressing cells was PS-dependent. TIM1-or TIM4-expressing Ba/F3 cells are known to capture PS-expressing exosomes; 12 thus it is plausible that CD300b does not bind TIM1 or TIM4 directly as previously proposed, 23 but rather associates with these proteins indirectly through associated PS-containing exosomes, or other PS-containing membrane fragments. With this line of reasoning, we hypothesized that the binding affinity of CD300b to TIM1-or TIM4-expressing Ba/F3 cells would increase after the addition of PS-coated liposomes.…”

“…22 Others have identified the PS-binding receptors TIM1 and TIM4 as endogenous ligands for CD300b, but not PS itself. 23 Here, we show that CD300b binds to PS, and recognizes PS on TIM1 or TIM4 expressing cells rather than TIM1 or TIM4 alone. We found that CD300b promotes PS-dependent apoptotic cell phagocytosis upon ectopic expression in cell lines, without the need for additional PS receptors.…”

“…A previous report demonstrated that CD300b recognized TIM1-or TIM4-expressing Ba/F3 cells. 23 To investigate further the binding of CD300b to TIM1 and TIM4, we generated TIM1-or TIM4-expressing Ba/F3 cell lines. We confirmed that Annexin V, as well as CD300b-Fc, bound to both cells but not EV-transduced cells (Figures 3a and b; Supplementary Figures 2a and b), and that EDTA treatment abolished that binding (Supplementary Figure 2c).…”

“…For instance, CD300b deficient mice are protected from ischemia/ reperfusion injury (IRI). 23 As the blockade of PS exposure on the cell surface by diannexin is able to improve kidney and liver IRI, 35,36 CD300b could be involved in IRI via PS recognition. In addition, CD300b-deficient mice are resistant to endotoxin and sepsis models.…”

Mammalian Target of Rapamycin Mediates Kidney Injury Molecule 1-Dependent Tubule Injury in a Surrogate Model

“…2 The binding motif WFND has been known to be essential for the phagocytic function of KIM-1. 21 The alignment of zKim-1 with mKIM-1 and hKIM-1 protein sequences demonstrated that the FND residues are conserved, while the tryptophan (W) residue is replaced with leucine (L) ( Figure 3C). The WFND motif is completely conserved in zKim-4.…”