Loss‐of‐function variants of triggering receptor expressed on myeloid cells 2 (TREM2) increase the risk of developing Alzheimer's disease (AD). The mechanism through which TREM2 contributes to the disease (TREM2 activation vs inactivation) is largely unknown. Here, we analyzed changes in a gene set downstream of TREM2 to determine whether TREM2 signaling is modified by AD progression. We generated an anti‐human TREM2 agonistic antibody and defined TREM2 activation in terms of the downstream expression changes induced by this antibody in microglia developed from human induced pluripotent stem cells (iPSC). Differentially expressed genes (DEGs) following TREM2 activation were compared with the gene set extracted from microglial single nuclear RNA sequencing data of patients with AD, using gene set enrichment analysis. We isolated an anti‐TREM2‐specific agonistic antibody, Hyb87, from anti‐human TREM2 antibodies generated using binding and agonism assays, which helped us identify 300 upregulated and 251 downregulated DEGs. Pathway enrichment analysis suggested that TREM2 activation may be associated with Th2‐related pathways. TREM2 activation was lower in AD microglia than in microglia from healthy subjects or patients with mild cognitive impairment. TREM2 activation also showed a significant negative correlation with disease progression. Pathway enrichment analysis of DEGs controlled by TREM2 activity indicated that TREM2 activation in AD may lead to anti‐apoptotic signaling, immune response, and cytoskeletal changes in the microglia. We showed that TREM2 activation decreases with AD progression, in support of a protective role of TREM2 activation in AD. In addition, the agonistic anti‐TREM2 antibody can be used to identify TREM2 activation state in AD microglia.

Progranulin (PGRN) haploinsufficiency associated with loss-of-function mutations in the granulin gene causes frontotemporal dementia (FTD). This suggests that increasing PGRN levels could have promising therapeutic implications for patients carrying GRN mutations. In this study, we explored the therapeutic potential of sortilin1 (SORT1), a clearance receptor of PGRN, by generating and characterizing monoclonal antibodies against SORT1. Anti-SORT1 monoclonal antibodies were generated by immunizing Sort1 knockout mice with SORT1 protein. The antibodies were classified into 7 epitope bins based on their competitive binding to the SORT1 protein and further defined by epitope bin-dependent characteristics, including SORT1-PGRN blocking, SORT1 down-regulation, and binding to human and mouse SORT1. We identified a positive correlation between PGRN up-regulation and SORT1 down-regulation. Furthermore, we also characterized K1-67 antibody via SORT1 down-regulation and binding to mouse SORT1 in vivo and confirmed that K1-67 significantly up-regulated PGRN levels in plasma and brain interstitial fluid of mice. These data indicate that SORT1 down-regulation is a key mechanism in increasing PGRN levels via anti-SORT1 antibodies and suggest that SORT1 is a potential target to correct PGRN reduction, such as that in patients with FTD caused by GRN mutation.

A large portosystemic shunt between the inferior mesenteric vein and the right internal iliac vein in a 28-yr-old non-cirrhotic man is presented. This collateral was discovered by ultrasound done as a screening examination for gastrointestinal bleeding. The direct communication of the inferior mesenteric vein with the internal iliac vein was demonstrated by computed tomography and percutaneous transhepatic portography. Surgical ligation of the collateral, performed to prevent future portosystemic encephalopathy, resulted in reduction of serum ammonia level and cessation of long-standing hemorrhoidal bleeding.

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Autoimmune responses to aquaporin 4 (AQP4) cause neuromyelitis optica (NMO); thus, specific immunotolerance to this self-antigen could represent a new NMO treatment. We generated the liposome-encapsulated AQP4 peptide 201-220 (p201-220) to induce immunotolerance. Liposomes were generated using phosphatidylserine and the polyglycidol species PG8MG. The in vivo tissue distribution of the liposomes was tested using an ex vivo imaging system. To confirm the antigen presentation capacity of PG8MG liposomes, dendritic cells were treated with PG8MG liposome-encapsulated AQP4 p201-220 (AQP4-PG8MG liposomes). Immunotolerance induction by AQP4-PG8MG liposomes was evaluated using the ex vivo cell proliferation of lymph node cells isolated from AQP4 p201-220-immunized AQP4-deficient mice. Fluorescent dye-labeled PG8MG liposomes were distributed to the lymph nodes. AQP4 p201-220 was presented on dendritic cells. AQP4-PG8MG liposomes were tended to suppress immune responses to AQP4 p201-220. Thus, the encapsulation of AQP4 peptides in PG8MG liposomes represents a new strategy for suppressing autoimmune responses to AQP4.

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