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An internal system designed to ward off and remove unnecessary or hazardous materials is intrinsic to animals. In addition to exogenous pathogens, a number of self-molecules, such as apoptotic or necrotic dead cells, their debris, and the oxides or peroxides of their cellular components, are recognized as extraneous substances. It is essential to eliminate these internal pathogens as quickly as possible because their accumulation can cause chronic inflammation as well as autoimmune responses, possibly leading to onset or progression of certain diseases. Apoptosis inhibitor of macrophage (AIM, also called CD5L) is a circulating protein that is a member of the scavenger receptor cysteine-rich superfamily, and we recently found that during acute kidney injury, AIM associates with intraluminal dead cell debris accumulated in renal proximal tubules and enhances clearance of luminal obstructions, thereby facilitating repair. Thus, AIM acts as a marker for phagocytes so that they can efficiently recognize and engulf the debris as their targets. In this chapter, we give an overview of the professional and non-professional phagocytes, and how soluble scavenging molecules such as AIM contribute to improvement of diseases by stimulating phagocytic activity.

A KIM-1–AIM interaction promotes clearance of cellular debris in renal tubules after acute kidney injury to improve disease outcome. Acute kidney injury (AKI) is associated with prolonged hospitalization and high mortality, and it predisposes individuals to chronic kidney disease. To date, no effective AKI treatments have been established. Here we show that the apoptosis inhibitor of macrophage (AIM) protein on intraluminal debris interacts with kidney injury molecule (KIM)-1 and promotes recovery from AKI. During AKI, the concentration of AIM increases in the urine, and AIM accumulates on necrotic cell debris within the kidney proximal tubules. The AIM present in this cellular debris binds to KIM-1, which is expressed on injured tubular epithelial cells, and enhances the phagocytic removal of the debris by the epithelial cells, thus contributing to kidney tissue repair. When subjected to ischemia-reperfusion (IR)-induced AKI, AIM-deficient mice exhibited abrogated debris clearance and persistent renal inflammation, resulting in higher mortality than wild-type (WT) mice due to progressive renal dysfunction. Treatment of mice with IR-induced AKI using recombinant AIM resulted in the removal of the debris, thereby ameliorating renal pathology. We observed this effect in both AIM-deficient and WT mice, but not in KIM-1–deficient mice. Our findings provide a basis for the development of potentially novel therapies for AKI.

Cell surface scavenger receptors contribute to homoeostasis and the response to pathogens and products associated with damage by binding to common molecular features on a wide range of targets. Apoptosis inhibitor of macrophage (AIM/CD5L) is a soluble protein belonging to the scavenger receptor cysteine-rich (SRCR) superfamily that contributes to prevention of a wide range of diseases associated with infection, inflammation, and cancer. AIM forms complexes with IgM pentamers which helps maintain high-levels of circulating AIM in serum for subsequent activation on release from the complex. The structural basis for AIM recognition of IgM as well as other binding targets is unknown. Here we apply cryogenic electron microscopy imaging (cryo-EM) to show how interfaces on both of AIM’s C-terminal SRCR domains interact with the Fcμ constant region and J chain components of the IgM core. Both SRCR interfaces are also shown to contribute interactions important for AIM binding to damage-associated molecular patterns (DAMPs). Here the authors use cryo-EM imaging to show how the AIM protein (apoptosis inhibitor of macrophage/CD5L) uses tandem scavenger receptor cysteine-rich domains to bind immunoglobulin M (IgM) using interactions also used to bind damage-associated molecular patterns (DAMPs).

Background Triglyceride-glucose (TyG) index has been proposed as a simple and credible surrogate for insulin resistance and an independent predictor of cardiovascular outcomes. Due to lack of data on TyG index in stroke, we aimed to evaluate the predictive value of the index for recurrent vascular event risk among stroke patients. Methods This was a prospective observational study, in which 866 patients (mean age, 70.1 years; male, 60.9%) with ischemic stroke (n = 781) or transient ischemic attack (n = 85) within 1 week of onset were consecutively enrolled and followed up for 1 year. The TyG index was calculated as ln (fasting triglycerides [mg/dL] × fasting glucose [mg/dL]/2). Patients were divided into 3 groups according to the tertile of TyG index levels: tertile 1, < 8.48; tertile 2, 8.48–9.01; and tertile 3, > 9.01. The primary outcome was a composite of major adverse cardiovascular events (MACE), including nonfatal stroke, nonfatal acute coronary syndrome, and vascular death. Results The median TyG index was 8.74 (interquartile range, 8.34–9.16). Higher levels of TyG index were significantly associated with increased prevalence of ipsilateral extracranial carotid ( P  = 0.032) and intracranial ( P  = 0.003) atherosclerotic stenosis. There were significant differences in the MACE risk between the three groups (annual rate, 8.6%, 11.6%, and 17.3% in the tertile 1, tertile 2, tertile 3 groups, respectively; log-rank P  = 0.005). After multivariable adjustments, the TyG index remains to be a significant predictor of MACE, with an adjusted hazard ratio for tertile 3 versus tertile 1 groups (95% confidence interval) of 2.01 (1.16–3.47). Similar results were also found for the risk of recurrent stroke. Conclusions TyG index is associated with cervicocerebral atherosclerosis and the MACE risk after a stroke, suggesting the potential value of TyG index to optimize the risk stratification of stroke patients. Trial registration URL:  https://upload.umin.ac.jp . Unique identifier: UMIN000031913.

The influence of excess salt intake on acute kidney injury (AKI) has not been examined precisely except for some clinical data, unlike in chronic kidney disease. Here, we addressed the influence of high salt (HS) on AKI and its underlying mechanisms in terms of the activity of circulating apoptosis inhibitor of macrophage (AIM, also called CD5L) protein, a facilitator of AKI repair. HS loading in mice subjected to ischemia/reperfusion (IR) resulted in high mortality with advanced renal tubular obstruction and marked exacerbation in biomarkers of proximal renal tubular damage. This AKI exacerbation appeared to be caused mainly by the reduced AIM dissociation from IgM pentamer in serum, as IgM-free AIM is indispensable for the removal of intratubular debris to facilitate AKI repair. Injection of recombinant AIM (rAIM) ameliorated the AKI induced by IR/HS, dramatically improving the tubular damage and mouse survival. The repair of lethal AKI by AIM was dependent on AIM/ kidney injury molecule-1 (KIM-1) axis, as rAIM injection was not effective in KIM-1 deficient mice. Our results demonstrate that the inhibition of AIM dissociation from IgM is an important reason for the exacerbation of AKI by HS, that AIM is a strong therapeutic tool for severe AKI.

Background Progressive multifocal leukoencephalopathy (PML) is a subacute onset demyelinating disease caused by JC virus and characterized by multifocal involvement of the subcortical white matter and cerebellar hemispheres or peduncles on magnetic resonance imaging (MRI). However, non-HIV PML patients with brain lesions limited to the cerebellum and brainstem have not been well characterized. Methods We report a 68-year-old man with systemic lupus erythematosus under treatment with immunosuppressants who developed non-HIV PML with brain lesions limited to the cerebellum and brainstem and successfully treated with a combination of mefloquine and mirtazapine. We performed a literature review to characterize patients with non-HIV PML with brain lesions limited to the cerebellum and brainstem. Results Eight cases with non-HIV brainstem/cerebellar form PML were identified including our case. All cases had compromised status related underlying diseases. Four (50%) had a good prognosis. Five cases were treated, including 3 with favourable outcomes. Between the good prognosis group ( n  = 4) and the poor prognosis group ( n  = 4), treatment status for PML and the interval between the initial manifestation and diagnosis did not differ. Among those who performed contrast-enhanced brain imaging, lesion enhancement was related to good prognosis (good prognosis group vs. poor prognosis group; 100% vs. 0%). Conclusion PML should be considered in the differential diagnosis of brain lesions limited to the cerebellum and brainstem in immunocompromised patients. The presence of immune response against JC virus and inflammatory reactions may indicate good prognosis in non-HIV brainstem/cerebellar form PML

BackgroundA diagnostic marker is needed enabling early and specific diagnosis of hepatocellular carcinoma (HCC) associated with non-alcoholic steatohepatitis (NASH). Our recent findings have indicated that circulating apoptosis inhibitor of macrophage (AIM), which usually associates with IgM pentamer in the blood, is activated by its dissociation from IgM. We investigated the serum levels of IgM-free AIM for AIM activation and its possible relationship with development of HCC in NASH.MethodsSerum levels of IgM-associated and IgM-free AIM were evaluated in patients with non-alcoholic fatty liver, NASH, and NASH-HCC using enzyme-linked immunosorbent assays and immunoblots. Liver biopsy specimens were graded and staged using Brunt’s classification.ResultsForty-two patients with fatty liver, 141 with NASH, and 26 with NASH-HCC were evaluated. Patients with stage 4 or grade 3 NASH (with or without HCC) exhibited significantly higher levels of both IgM-free and total AIM than those with fatty liver, whereas the ratio of IgM-free-to-total AIM was equivalent in these groups. Among patients with the same fibrosis stage of NASH, those with HCC had significantly higher IgM-free but not total AIM levels, resulting in a proportional increase in the IgM-free/total AIM ratio. Analysis of the areas under the receiver operating characteristic curves indicated the high sensitivity of the IgM-free AIM for NASH-HCC.ConclusionsOur observations suggest the activation of AIM in blood in the presence of NASH-HCC, with a significant increase in IgM-free AIM levels. IgM-free AIM serum levels appear to be a sensitive diagnostic marker for NASH-HCC.

Objective To identify pathways linking cytokine abnormalities to mortality via prognostic factors in patients with anti-melanoma differentiation-associated protein 5 antibodies (anti-MDA5 Ab). Methods This study included patients with anti-MDA5 Ab whose serum was available. Serum cytokine levels were measured using a multiplex bead assay. Prognostic factors were identified using Cox regression and log-rank test. Prognostic factor groups were identified using principal component analysis (PCA) and factor and cluster analyses. The association between cytokine levels and prognostic factors (groups) was examined using PCA and correlation and path analyses. A prognosis-prediction model was developed using prognostic factors from the different groups. Results Thirty-five patients were included in this study, of whom 31 had rapidly progressive interstitial lung disease (RP-ILD), and 14 died. We identified white blood cell (WBC), gamma-glutamyl transpeptidase (γ-GTP), lactate dehydrogenase (LDH), C-reactive protein (CRP), ferritin, and ILD-related factors (Krebs von den Lungen-6 [KL-6], surfactant protein D [SP-D], and CT score) as prognostic factors, in addition to von Willebrand factor and thrombomodulin. Two prognostic factor groups were found: Group 1 included WBC, CRP, and ILD-related factors, and Group 2 included ferritin, LDH, and γ-GTP. Both groups contributed to mortality. Group 1 was associated with IL-6, and Group 2 was related to IL-6, IL-10, and IP-10, and indirectly with TNF-α. A model using CRP (Group1) and γ-GTP (Group2) achieved an area under the curve of 0.84, which was not inferior to previously reported models. Conclusions Two pathways leading to poor prognosis were identified in anti-MDA5-Ab-positive patients, each marked by specific cytokine abnormalities.

Obesity is associated with various metabolic and cardiovascular diseases caused by chronic, low-grade inflammation that is initially observed in obese adipose tissue. In addition, many etiological studies in humans have shown a strong correlation between obesity and inflammatory autoimmune diseases. In this review, we focus on the involvement of apoptosis inhibitor of macrophage (AIM), a macrophage-derived blood protein, in both types of immune response. Through differential mechanisms, AIM thereby plays key roles in the pathogenesis of atherosclerosis, metabolic diseases, and obesity-associated autoimmune diseases. Thus, the regulation of blood AIM levels or AIM function has the potential to serve as a next-generation therapy against these inflammatory diseases brought about by modern lifestyle.

Non-tuberculous mycobacteria infections, including Mycobacterium avium , are increasingly recognized as a growing public health concern, even among immunocompetent individuals. These infections are a significant cause of chronic pulmonary disease, and they are characterized by the formation of foamy macrophages (FMs) that facilitate bacterial persistence. Previously, we reported that apoptosis inhibitor of macrophage (AIM), a protein secreted by macrophages, promotes lipid droplet accumulation in M. avium -infected macrophages. However, the precise role of AIM in modulating immune responses remains unclear. This study aimed to elucidate the effect of AIM on FM formation, bacterial burden, and immune response in M. avium -infected mice by comparing AIM knockout (KO) mice with wild-type mice. Histological analysis revealed a reduction in FM formation in AIM KO mice, accompanied by decreased lipid droplet accumulation and altered expression of lipid metabolism-related genes. Furthermore, AIM KO mice exhibited a reduced bacterial load in the lungs, highlighting decreased cytokine production, including IL-1β, compared to wild-type mice. In addition, the analysis of the immune cells of AIM KO mice using flow cytometry revealed an increase in M1 macrophages and IFN-γ-producing T cells, as well as a decrease in M2 macrophages and interleukin 10 (IL-10)-producing T cells. The reduced expression of CD36 and PD-L1 in macrophages from AIM KO mice further supports the skewing toward an M1 phenotype. In vitro experiments with bone marrow-derived macrophages (BMDMs) confirmed reduced bacterial growth and lipid droplet formation in AIM KO BMDMs, which was restored by AIM and IL-10 treatment. These findings suggest that AIM contributes to the promotion of FM formation by establishing an immunosuppressive environment that promotes the establishment of M. avium through IL-10 production.