Alzheimer’s disease (AD) and mixed dementia (MxD) comprise the majority of dementia cases in the growing global aging population. MxD describes the coexistence of AD pathology with vascular pathology, including cerebral small vessel disease (SVD). Cardiovascular disease increases risk for AD and MxD, but mechanistic synergisms between the coexisting pathologies affecting dementia risk, progression and the ultimate clinical manifestations remain elusive. To explore the additive or synergistic interactions between AD and chronic hypertension, we developed a rat model of MxD, produced by breeding APPswe/PS1ΔE9 transgenes into the stroke-prone spontaneously hypertensive rat (SHRSP) background, resulting in the SHRSP/FAD model and three control groups (FAD, SHRSP and non-hypertensive WKY rats, n = 8–11, both sexes, 16–18 months of age). After behavioral testing, rats were euthanized, and tissue assessed for vascular, neuroinflammatory and AD pathology. Hypertension was preserved in the SHRSP/FAD cross. Results showed that SHRSP increased FAD-dependent neuroinflammation (microglia and astrocytes) and tau pathology, but plaque pathology changes were subtle, including fewer plaques with compact cores and slightly reduced plaque burden. Evidence for vascular pathology included a change in the distribution of astrocytic end-foot protein aquaporin-4, normally distributed in microvessels, but in SHRSP/FAD rats largely dissociated from vessels, appearing disorganized or redistributed into neuropil. Other evidence of SVD-like pathology included increased collagen IV staining in cerebral vessels and PECAM1 levels. We identified a plasma biomarker in SHRSP/FAD rats that was the only group to show increased Aqp-4 in plasma exosomes. Evidence of neuron damage in SHRSP/FAD rats included increased caspase-cleaved actin, loss of myelin and reduced calbindin staining in neurons. Further, there were mitochondrial deficits specific to SHRSP/FAD, notably the loss of complex II, accompanying FAD-dependent loss of mitochondrial complex I. Cognitive deficits exhibited by FAD rats were not exacerbated by the introduction of the SHRSP phenotype, nor was the hyperactivity phenotype associated with SHRSP altered by the FAD transgene. This novel rat model of MxD, encompassing an amyloidogenic transgene with a hypertensive phenotype, exhibits several features associated with human vascular or “mixed” dementia and may be a useful tool in delineating the pathophysiology of MxD and development of therapeutics.

Dendritic cells (DC) that primarily reside in tissues carry antigens to local lymphoid organs to induce immunity or tolerance. We posit that a defect in the migration of tissue-DCs may predispose to autoimmunity in a tissue-specific manner; and an improved migration of tissue-DC may ameliorate disease in the respective organ. Here, we demonstrate that treatment of lupus dermatitis-prone MRL-lpr and MRL+/+ mice that exhibit a profound defect in the migration of skin-DC with a glycolipid αGalCer reduced the severity of dermatitis and enhanced the migration of skin-DCs, more so in Langerhans cells (LC; p=0.004) than in Lang+dDC (p=0.03). This effect of αGalCer was independent of its effect on iNKT cells, but required the presence of CD1d. Furthermore, αGalCer treatment enhanced the numbers of epidermis-resident γδ T cells in MRL-lpr mice that had reduced numbers of γδ T cells as compared to MHC-matched control mice. Finally, gd T cell-deficient mice had reduced skin-DC migration, and isolated skin-gd T cells directly promoted the migration of LC via CD40L-CD40 interaction. These data elucidate a new mechanism of regulation of skin-DC homeostasis whereby skin-gd T cells normally facilitate LC migration from skin to cutaneous lymph node. Such ‘local’ control of migratory behavior of tissue-DC can regulate immune response in a tissue-specific manner. This mechanism of skin-DC homeostasis is disrupted in lupus dermatitis, but can be repaired by treatment with a glycolipid.

Ocular surface inflammation is common and sometimes severe in autoimmune diseases. Little is known about the role of cornea-resident dendritic cells, including Langerhans cells (LC), in ocular surface autoimmunity. Here, we analyzed corneal LC in autoimmune-prone MRL mice. LC (CD11c+ CD207+) were more abundant and activated (CD86+ CD40+) in the corneal epithelium of MRL mice than of B6 mice. However, LC were ~5-fold lower in the corneal stroma of MRL mice than of B6 mice. LC in cervical lymph nodes were also lower in MRL mice than in B6 mice. Ongoing studies will examine whether the increase of activated LC in corneal epithelium, but their reduction in corneal stroma and eye-draining lymph nodes in autoimmune mice is due to a defect in the migration of LC from the cornea to eye-draining lymph nodes. Since LC are believed to carry antigens from tissues to their respective draining lymph nodes to maintain tolerance in a tissue-specific manner, the reduced LC in eye-draining lymph nodes may lead to the breakdown of tolerance to eye antigens. To directly test the role of LC in ocular autoimmunity, we introgressed the Lang-eGFP.DTR knockin mutation from the stock B6 mice that express diphtheria toxin receptor (DTR) driven by Langerin promoter (Malissen, 2005) onto the MRL background. Diphtheria toxin injections depleted LC in Lang-eGFP.DTR MRL mice and accelerated corneal inflammation. Taken together, these data suggest a protective role of LC in corneal inflammation.

Abstract Glycolipid antigens such as αGalCer and phospholipid (PL) antigens such as phosphatidyl choline bind CD1d and activate T cells. Extensive work on αGalCer-reactive T cells has identified their pathogenic or protective roles in inflammation, infection and cancer. Little is known about the biology and functions of CD1d-restricted PL-reactive T (PL-T) cells. Here, we identified T cells that recognize a battery of PL antigens loaded onto mouse CD1d in various lymphoid organs. While CD1d/PL-T cells were fewer than CD1d/αGalCer-reactive T cells in the liver and spleen, PL-T cells were relatively more abundant than glycolipid-reactive T cells in organs such as mouse decidua. The CD1d/PL-T cells secreted IFN-γ upon in vivo priming with PL antigens in an antigen-specific manner. The PL-T cells did not stain with CD1d/αGalCer tetramers and did not respond to glycolipid antigen αGalCer. Intriguingly, activation of CD1d/PL-T cells markedly reduced the proliferation of αGalCer-reactive T cells in vitro, ex vivo, and in vivo. Thus, PL-T cells are a subset of CD1d-restricted T cells that are phenotypically and functionally distinct from glycolipid-reactive T cells. PL-T cells also negatively regulate the function of glycolipid-reactive T cells. Ongoing studies will investigate whether PL-T cells will modulate the pathogenic and protective roles of glycolipid-reactive T cells in various immune-mediated conditions.

Abstract Plasmacytoid dendritic cells (pDC) develop and proliferate in bone marrow and migrate to peripheral organs. pDCs produce IFNα and play a role in viral infections and autoimmune diseases. Mechanisms that regulate the development of pDC in the bone marrow are not fully understood. Invariant natural killer T (iNKT) cells comprise of a small population of lymphocytes in the bone marrow. Here, we examined the role of iNKT cells on pDC population in the bone marrow in vivo and in vitro. Bone marrow cells from wild-type, CD1d-deficient, and iNKT cell transgenic (Vα14-Tg) BALB/c mice were cultured with Flt3 ligand (FL) and αGalCer. We found that although all DCs were activated, as determined by expression of MHCII and CD86, in the presence of activated iNKT cells, the proportion of pDCs (CD11c+PDCA1+B220+) was consistently reduced in the presence of activated iNKT cells. Similar results were found in vivo, where an injection of FL and αGalCer reduced the proportion of pDCs, whereas the proportion of myeloid DCs (CD11c+CD11b+) was unchanged or slightly increased, in the bone marrow and spleen. Interestingly, FL+αGalCer increased CCR7 expression on bone marrow pDCs, but not on myeloid DCs, suggesting that iNKT cells may contribute to the egress of pDCs from the bone marrow. Such effect of FL+αGalCer injection was not seen in CD1d-deficient mice. In summary, these data suggest a role of iNKT cells in the development and homeostasis of pDCs.

Abstract Tissue-resident DC carry antigens to tissue-draining lymph nodes (LN) to induce immunity. To investigate the role of this DC function in the pathogenesis of autoimmune disease, we analyzed the migration of skin-resident DC, namely Langerhans cells (LC) and dermal DC, in lupus dermatitis. LC and dermal DC, but not blood-derived DC, from lupus-prone MRL-lpr and MRL+/+ mice exhibited defects in their ability to emigrate from the epidermis, to migrate through dermal lymphatics, and to immigrate into LN (JI 2008). Since conventional DC migration assays require DC activation, we used Lang-EGFP knock-in (KI) mice to visualize LC at steady-state. EGFP+ cells (LC) were lower in LN of KI MRL mice than of KI B6 mice, thus confirming what we found using inbred mice. Importantly, skin DC migration defect precedes disease and correlates with the severity of dermatitis. Conversely, treatment with αGalCer restores skin DC migration and ameliorates dermatitis. Surprisingly, αGalCer-mediated increase in skin DC migration does not require NKT cells, but is associated with epidermal γδ T cell (eγδT) expansion in a CD1d-dependent manner. Finally, eγδT are reduced in MRL mice, and deficiency of CD1d or eγδT, but not of NKT, reduces skin DC migration and worsens dermatitis. Thus, we elucidate a novel mechanism, whereby CD1d-dependent eγδT normally facilitate skin DC migration. This regulatory mechanism is impaired in lupus dermatitis, providing evidence for a novel mechanism of autoimmune disease.