Humanized mice are invaluable models for investigating human cell engraftment in vivo post-transplantation. Mice engrafted with human red blood cells (hRBCs) are useful for examining the physiological roles of hRBCs in vivo, including studies on blood disorders, immune responses, and transfusion-related research. These models hold promise for malaria infection studies and vaccine development. However, engrafted hRBCs in vivo in immunodeficient mice presents challenges that must be addressed to establish effective in vivo models. In this study, we explored the rejection mechanisms of hRBCs in immunodeficient NOD/Shi-scid-IL2rγnull (NOG) mice and developed a novel model for long-term RBC engraftment. We observed rapid depletion of fluorescent-labeled hRBCs in the liver, but not in other organs, of NOG mice, with Gr-1midCD68+ mouse macrophages play a significant role in the elimination of hRBCs in the liver. To counteract this, we created thymidine kinase (TK) transgenic (Tg) mice under the human CD68 promoter (NOG-pCD68-TK Tg), which, upon administration of valganciclovir (VGCV), led to the successful depletion of macrophages. Consequently, hRBCs showed significantly prolonged engraftment in NOG-pCD68-TK Tg mice compared to non-Tg mice following macrophage depletion, maintaining engraftment for up to 14 days post-transplantation. This study elucidates the erythrophagocytosis mechanisms of hRBCs in mice and establishes NOG-pCD68-TK Tg mice as a valuable model for the long-term engraftment of hRBCs, potentially advancing in vivo hRBC research.

Autoimmune sialadenitis is a hallmark of IgG4-related disease (IgG4-RD) and Sjögren syndrome (SS). The single-stranded RNA sensor TLR7 has been shown as a driver of sialadenitis. Although TLR7 is activated by ssRNA degradation products such as nucleosides and oligoribonucleotides, the role of these ligands in sialadenitis development remains unclear. Here, we demonstrate that lysosomal accumulation of endogenous nucleosides is sufficient to drive autoimmune sialadenitis. Loss-of-function genetic variations in the nucleoside transporter SLC29A3 cause lysosomal nucleoside accumulation, leading to constitutive activation of TLR7 and TLR8 in monocytes and macrophages. Consequently, macrophages infiltrate multiple organs in mice and humans. In Slc29a3‒/‒ mice, submandibular glands (SMGs) were impaired in saliva production. SLC29A3-deficiency specifically damaged Aqp5+ acinar and intercalated duct cells in SMGs, while sparing neighboring cells such as ductal and myoepithelial cells. Although macrophages accumulated in both the spleen and SMGs, lymphocyte infiltration and production of chemokines including CXCL9, CXCL13, and CCL5 occurred selectively in SMGs. In IgG4-RD patients, these chemokines were also produced in SMGs, highlighting parallels between sialadenitis in Slc29a3‒/‒ mice and IgG4-RD. These findings indicate that constitutive TLR7 activation by nucleosides is a key mechanism driving autoimmune sialadenitis.

The human gastrointestinal tract is a unique mucosal barrier with a tremendous surface area that is subject to continuous exposure to the environment. The immune system must remain poised to protect this organ system from potential pathogens while restraining chronic inflammatory responses that negatively impact physiological functions or facilitate malignancy. Innate lymphocytes emerged as major regulators of gut health through numerous key functions. Recent evidence indicates that these cells are adaptably influenced by specialized microniches, or distinct aggregates of cells that engage in dynamic crosstalk at a microscopic level and integrate signals from the environment to perform specialized functions with regional precision. Here we explore our current understanding of how microniches in the gut shape the biology of innate lymphocytes, with a focus on an interplay of diet and microbial exposure, selective cell-cell communication networks, and spatiotemporal properties. We also discuss how these microniches may be altered in human diseases or could be harnessed to better protect the gut. Finally, we identify current gaps in knowledge in this rapidly emerging field.

Fasting is known to alter the circulation dynamics of immune cells, including T cells, by shifting them from peripheral tissues to the bone marrow (BM), where they enter a quiescent state to avoid starvation stress and acquire apoptosis resistance through upregulation of BCL2. Upon refeeding, these T cells exit the BM and return to circulation. In solid tumors, fasting-refeeding not only affects the trafficking of CD8+ T cells between tumors and their draining lymph nodes (dLNs); but also modulates the antitumor immune response. In this study, we investigated how metformin's antitumor responses are affected by repeated fasting-refeeding cycles. Metformin administration combined with weekly 48-hour fasting showed a synergistic antitumor effect, which was abolished by in vivo depletion of CD8+ T cells. Immunohistofluorescence staining showed that fasting reduced CD8+T cells in tumors and dLNs while increasing their presence in the BM; refeeding reversed this distribution. Refeeding also increased the expression of Ifng, Gzmb, Tnf, and Tbx21 in tumors. Likewise, Cxcr6, Cxcl16, and Vcam1 expression levels were elevated only upon refeeding. Notably, CXCR6 was exclusively expressed on CD62L- effector memory T cells (TEM). The antitumor effect induced by the combinational therapy was abolished by administration of an anti-VCAM-1 neutralizing antibody. Our findings demonstrate that combining metformin with fasting exerts a synergistic antitumor effect by recruiting CD8+ T cells-relocated to the BM during fasting-back to the tumor during refeeding, facilitated by enhanced VCAM-1 expression on normalized tumor vasculature.

In a typical immune response, naïve B cells are activated, differentiate into short-lived plasma cells (SLPCs), and then mature into long-lived plasma cells (LLPCs) in the bone marrow. Among three TNF family receptors (BAFF-R, TACI, and BCMA), BAFF-R and BCMA are known to be crucial for the maintenance of naïve B cells and bone marrow LLPCs, respectively. In contrast, the function of TACI remains unclear, as analysis of global TACI knockout mice suggests the existence of two opposing roles in B and plasma cells. Here, to define the role of TACI during T-dependent (TD) immune responses in a B and plasma cell-intrinsic manner, we utilized adoptive transfer experiments employing B cells with a conditional TACI knockout. We show that B cell activation is apparently normal in the absence of TACI, while it is crucial for the expansion of IgM+ and IgG1+ SLPCs and maintenance of their resultant bone marrow LLPCs. Hence, our data suggest that the hyper-B cell activation seen in global TACI knockout mice could be due to an indirect control of BAFF levels or B cell extrinsic anomalies.

We previously identified Alcaligenes as symbiotic bacteria residing within Peyer's patches and demonstrated that their primary components, lipopolysaccharides, and their active center, lipid A, are excellent adjuvants for mucosal vaccination. Here, we evaluated the effectiveness of Alcaligenes-derived lipid A as an adjuvant for sublingual immunization, a novel vaccination route. Mice sublingually immunized with Alcaligenes lipid A and ovalbumin (OVA) showed enhanced production of OVA-specific IgA in both the respiratory and gastrointestinal tracts. In addition, increased serum levels of OVA-specific and IgG antibodies were elicited through germinal center reactions in the draining lymph nodes without excessive inflammation at the administration sites. These results demonstrated superior efficacy not previously achieved through other routes of administration (e.g., intranasal, subcutaneous, intramuscular administration) or by existing adjuvants (e.g., CpG-ODN). In addition, sublingual immunization with cholera toxin B subunit (CTB) and lipid A led to an elevated CTB-specific IgG response in the systemic compartment and an elevated IgA response in the intestinal tract, effectively suppressing the diarrhea induced by oral challenge with cholera toxin. Furthermore, immunization with pneumococcal surface protein A (PspA) plus Alcaligenes lipid A elicited strong PspA-specific CD4+ T cell proliferation and Th17 responses, as well as IgA and IgG responses, in both the respiratory tract and the systemic compartment. These effects enhanced pneumococcal clearance in the lungs and subsequent protection against Streptococcus pneumoniae infection. Together, our findings suggest that Alcaligenes-derived lipid A is a potent sublingual vaccine adjuvant with potential efficacy against both respiratory and intestinal infectious diseases.