New roles for TIM family members in immune regulation. Nat Rev Immunol. 2008;8:577-580. [PMID: 18617884 DOI: 10.1038/nri2366]

T-cell immunoglobulin and mucin domain 1 (TIM-1) is a receptor for Zaire Ebolavirus and Lake Victoria Marburgvirus

The glycoproteins (GP) of enveloped viruses facilitate entry into the host cell by interacting with specific cellular receptors. Despite extensive study, a cellular receptor for the deadly filoviruses Ebolavirus and Marburgvirus has yet to be identified and characterized. Here, we show that T-cell Ig and mucin domain 1 (TIM-1) binds to the receptor binding domain of the Zaire Ebola virus (EBOV) glycoprotein, and ectopic TIM-1 expression in poorly permissive cells enhances EBOV infection by 10- to 30-fold. Conversely, reduction of cell-surface expression of TIM-1 by RNAi decreased infection of highly permissive Vero cells. TIM-1 expression within the human body is broader than previously appreciated, with expression on mucosal epithelia from the trachea, cornea, and conjunctiva--tissues believed to be important during in vivo transmission of filoviruses. Recognition that TIM-1 serves as a receptor for filoviruses on these mucosal epithelial surfaces provides a mechanistic understanding of routes of entry into the human body via inhalation of aerosol particles or hand-to-eye contact. ARD5, a monoclonal antibody against the IgV domain of TIM-1, blocked EBOV binding and infection, suggesting that antibodies or small molecules directed against this cellular receptor may provide effective filovirus antivirals.

Coexpression of Tim-3 and PD-1 identifies a CD8+ T-cell exhaustion phenotype in mice with disseminated acute myelogenous leukemia

Tumor-associated immune suppression can lead to defective T cell-mediated antitumor immunity. Here, we identified a unique phenotype of exhausted T cells in mice with advanced acute myelogenous leukemia (AML). This phenotype is characterized by the coexpression of Tim-3 and PD-1 on CD8(+) T cells in the liver, the major first site of AML metastases. PD-1 and Tim-3 coexpression increased during AML progression. PD-1(+)Tim-3(+) CD8(+) T cells were deficient in their ability to produce IFN-γ, TNF-α, and IL-2 in response to PD-1 ligand (PDL1) and Tim-3 ligand (galectin-9) expressing AML cells. PD-1 knockout (KO), which were partially resistant to AML challenge, up-regulated Tim-3 during AML progression and such Tim-3(+)PD-1- KO CD8(+) T cells had reduced cytokine production. Galectin-9 KO mice were more resistant to AML, which was associated with reduced T-regulatory cell accumulation and a modest induction of PD-1 and Tim-3 expression on CD8(+) T cells. Whereas blocking the PD-1/PDL1 or Tim-3/galectin-9 pathway alone was insufficient to rescue mice from AML lethality, an additive effect was seen in reducing-albeit not eliminating-both tumor burden and lethality when both pathways were blocked. Therefore, combined PD-1/PDL1 and Tim-3/galectin-9 blockade may be beneficial in preventing CD8(+) T-cell exhaustion in patients with hematologic malignancies such as advanced AML.

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

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.

Galectin-9/TIM-3 interaction regulates virus-specific primary and memory CD8 T cell response

In this communication, we demonstrate that galectin (Gal)-9 acts to constrain CD8(+) T cell immunity to Herpes Simplex Virus (HSV) infection. In support of this, we show that animals unable to produce Gal-9, because of gene knockout, develop acute and memory responses to HSV that are of greater magnitude and better quality than those that occur in normal infected animals. Interestingly, infusion of normal infected mice with alpha-lactose, the sugar that binds to the carbohydrate-binding domain of Gal-9 limiting its engagement of T cell immunoglobulin and mucin (TIM-3) receptors, also caused a more elevated and higher quality CD8(+) T cell response to HSV particularly in the acute phase. Such sugar treated infected mice also had expanded populations of effector as well as memory CD8(+) T cells. The increased effector T cell responses led to significantly more efficient virus control. The mechanisms responsible for the outcome of the Gal-9/TIM-3 interaction in normal infected mice involved direct inhibitory effects on TIM-3(+) CD8(+) T effector cells as well as the promotion of Foxp3(+) regulatory T cell activity. Our results indicate that manipulating galectin signals, as can be achieved using appropriate sugars, may represent a convenient and inexpensive approach to enhance acute and memory responses to a virus infection.

Galectin-9/TIM-3 interaction regulates virus-specific primary and memory CD8 T cell response

In this communication, we demonstrate that galectin (Gal)-9 acts to constrain CD8(+) T cell immunity to Herpes Simplex Virus (HSV) infection. In support of this, we show that animals unable to produce Gal-9, because of gene knockout, develop acute and memory responses to HSV that are of greater magnitude and better quality than those that occur in normal infected animals. Interestingly, infusion of normal infected mice with alpha-lactose, the sugar that binds to the carbohydrate-binding domain of Gal-9 limiting its engagement of T cell immunoglobulin and mucin (TIM-3) receptors, also caused a more elevated and higher quality CD8(+) T cell response to HSV particularly in the acute phase. Such sugar treated infected mice also had expanded populations of effector as well as memory CD8(+) T cells. The increased effector T cell responses led to significantly more efficient virus control. The mechanisms responsible for the outcome of the Gal-9/TIM-3 interaction in normal infected mice involved direct inhibitory effects on TIM-3(+) CD8(+) T effector cells as well as the promotion of Foxp3(+) regulatory T cell activity. Our results indicate that manipulating galectin signals, as can be achieved using appropriate sugars, may represent a convenient and inexpensive approach to enhance acute and memory responses to a virus infection.

Phosphatidylserine receptor Tim-4 is essential for the maintenance of the homeostatic state of resident peritoneal macrophages

Tim-4 is a phosphatidylserine (PS) receptor that is expressed on various macrophage subsets. It mediates phagocytosis of apoptotic cells by peritoneal macrophages. The in vivo functions of Tim-4 in phagocytosis and immune responses, however, are still unclear. In this study, we show that Tim-4 quickly forms punctate caps on contact with apoptotic cells, in contrast to its normal diffused expression on the surface of phagocytes. Despite its expression in marginal zone and tingible body macrophages, Tim-4 deficiency only minimally affects outcomes of several acute immune challenges, including the trapping of apoptotic cells in the marginal zone, the clearance apoptotic cells by tingible body macrophages, and the formation of germinal centers and elicitation of antibody responses against sheep red blood cells (SRBCs). In addition, Tim-4(-/-) resident peritoneal macrophages (rPMs) phagocytose necrotic cells and other opsonized targets normally. However, their ability to bind and engulf apoptotic cells is significantly compromised both in vitro and in vivo. Most importantly, Tim-4 deficiency results in increased cellularity in the peritoneum. Resting rPMs produce higher TNF-alpha in culture. Their response to LPS, on the contrary, is dampened. Our data support an indispensible role of Tim-4 in maintaining the homeostasis of rPMs.

T and B cell hyperactivity and autoimmunity associated with niche-specific defects in apoptotic body clearance in TIM-4-deficient mice

TIM-4, a member of the TIM family expressed on antigen-presenting cells, binds to phosphatidylserine exposed on the surface of apoptotic bodies. However, the significance of this interaction in vivo remains unknown because other receptors have been implicated in the clearance of apoptotic bodies and could compensate for the TIM-4 deficiency in vivo. In this study, we describe the generation of TIM-4-deficient mice and address whether TIM-4 serves a unique function in vivo. We show that TIM-4(-/-) peritoneal macrophages and B-1 cells do not efficiently engulf apoptotic bodies in vitro, or clear apoptotic bodies in vivo. TIM-4-deficient mice have hyperactive T and B cells, elevated levels of serum Ig, and develop antibodies to double-stranded DNA. Taken together, we show that TIM-4 is critical for the clearance of apoptotic bodies in vivo, and that lack of TIM-4 results in aberrant persistence of apoptotic bodies leading to dysregulated lymphocyte activation and signs of systemic autoimmunity.

Cell surface and secreted protein profiles of human thyroid cancer cell lines reveal distinct glycoprotein patterns

Cell surface proteins have been shown to be effective therapeutic targets. In addition, shed forms of these proteins and secreted proteins can serve as biomarkers for diseases, including cancer. Thus, identification of cell surface and secreted proteins has been a prime area of interest in the proteomics field. Most cell surface and secreted proteins are known to be glycosylated, and therefore, a proteomics strategy targeting these proteins was applied to obtain proteomic profiles from various thyroid cancer cell lines that represent the range of thyroid cancers of follicular cell origin. In this study, we oxidized the carbohydrates of secreted proteins and those on the cell surface with periodate and isolated them via covalent coupling to hydrazide resin. The glycoproteins obtained were identified from tryptic peptides and N-linked glycopeptides released from the hydrazide resin using two-dimensional liquid chromatography-tandem mass spectrometry in combination with the gas phase fractionation. Thyroid cancer cell lines derived from papillary thyroid cancer (TPC-1), follicular thyroid cancer (FTC-133), Hurthle cell carcinoma (XTC-1), and anaplastic thyroid cancer (ARO and DRO-1) were evaluated. An average of 150 glycoproteins were identified per cell line, of which more than 57% are known cell surface or secreted glycoproteins. The usefulness of the approach for identifying thyroid cancer associated biomarkers was validated by the identification of glycoproteins (e.g., CD44, galectin 3 and metalloproteinase inhibitor 1) that have been found to be useful markers for thyroid cancer. In addition to glycoproteins that are commonly expressed by all of the cell lines, we identified others that are only expressed in the more well-differentiated thyroid cancer cell lines (follicular, Hurthle cell and papillary), or by cell lines derived from undifferentiated tumors that are uniformly fatal forms of thyroid cancer (i.e., anaplastic). On the basis of the results obtained, a set of glycoprotein biomarker candidates for thyroid cancer is proposed.

Innate receptors and microbes in induction of autoimmunity

Cells of the adaptive immune system (T and B cells) causing autoimmunity require activation signals that are normally provided by the innate immune system. Innate signaling receptors are obvious candidates for participation in the induction of autoimmunity, and the nature of these receptors suggests that microbes could be the triggers. Recent publications describing the development of autoimmunity in sterile conditions and in animals deficient in innate signaling question the requirement of these receptors for initiation of autoimmunity. In addition, the role of the non-pathogenic (commensal) microbiota as a regulator of autoimmunity has come into the spotlight. In this review we discuss recent reports that deal with the link between innate signaling receptors and 'adaptive' autoimmunity.

Sequence, structure, function, immunity: structural genomics of costimulation

SUMMARY

Costimulatory receptors and ligands trigger the signaling pathways that are responsible for modulating the strength, course, and duration of an immune response. High-resolution structures have provided invaluable mechanistic insights by defining the chemical and physical features underlying costimulatory receptor:ligand specificity, affinity, oligomeric state, and valency. Furthermore, these structures revealed general architectural features that are important for the integration of these interactions and their associated signaling pathways into overall cellular physiology. Recent technological advances in structural biology promise unprecedented opportunities for furthering our understanding of the structural features and mechanisms that govern costimulation. In this review, we highlight unique insights that have been revealed by structures of costimulatory molecules from the immunoglobulin and tumor necrosis factor superfamilies and describe a vision for future structural and mechanistic analysis of costimulation. This vision includes simple strategies for the selection of candidate molecules for structure determination and highlights the critical role of structure in the design of mutant costimulatory molecules for the generation of in vivo structure-function correlations in a mammalian model system. This integrated 'atoms-to-animals' paradigm provides a comprehensive approach for defining atomic and molecular mechanisms.

Role of Tim-3/galectin-9 inhibitory interaction in viral-induced immunopathology: shifting the balance toward regulators

Controlling chronic immunoinflammatory diseases such as lesions in the eye caused by infection with HSV represents a therapeutic challenge. Since CD4(+) T cells are the primary orchestrators of lesions, targeting activated CD4(+) T cell subsets and increasing the representation of cells that express regulatory function would be a logical therapeutic approach. We show that this outcome can be achieved by therapy, systemic or local, with the lectin family member galectin-9. This molecule, which is a natural product of many cell types, acts as a ligand to the inhibitory molecule TIM-3 (T cell Ig and mucin-3) that is expressed by activated but not naive T cells. We show that 50% or more of T cells in ocular lesions caused by HSV in mice express TIM-3 and that blocking signals from its natural ligand with a mAb results in more severe lesions. More importantly, the provision of additional galectin-9, either systemically or more effectively by local subconjuctival administration, diminished the severity of stromal keratitis lesions as well as the extent of corneal neovascularization. Multiple mechanisms were involved in inhibitory effects. These included apoptosis of the orchestrating effector T cells with consequent reduction of proinflammatory cytokines and an increase in the representation of two separate subtypes of regulatory cells as well as inhibitory effects on the production of molecules involved in neovascularization, an essential component of stromal keratitis pathogenesis. Our results indicate that galectin-9 therapy may represent a useful approach to control HSV-induced lesions, the most common cause of infectious blindness in the Western world.

Involvement of Sema4A in the progression of experimental autoimmune myocarditis

Dilated cardiomyopathy often results from autoimmunity triggered by microbial infections during myocarditis. However, it remains unclear how immunological disorders are implicated in pathogenesis of autoimmune myocarditis. Here, we demonstrated that Sema4A, a class IV semaphorin, plays key roles in experimental autoimmune myocarditis (EAM). Dendritic cells pulsed with myosin heavy chain-alpha peptides induced severe myocarditis in wild-type mice, but not in Sema4A-deficient mice. In adoptive transfer experiments, CD4+ T-cells from wild-type mice induced severe myocarditis, while CD4+ T-cells from Sema4A-deficient mice exhibited considerably attenuated myocarditis. Our results indicated that Sema4A is critically involved in EAM by regulating differentiation of T-cells.