Endogenous Expression of the Human CD83 Attenuates EAE Symptoms in Humanized Transgenic Mice and Increases the Activity of Regulatory T Cells

Advances in bacterial artificial chromosome (BAC) transgenic mice for gene analysis and disease research

Transgenic mice, including those created using Bacterial Artificial Chromosomes (BACs), are artificial manipulations that have become critical tools for studying gene function. While conventional transgenic techniques face challenges in achieving precise expression of foreign genes in specific cells and tissues, BAC transgenic mice offer a solution by incorporating large DNA segments that can include entire expression units with tissue-specific enhancers. This review provides a thorough examination of BAC transgenic mouse technology, encompassing both traditional and humanized models. We explore the benefits and drawbacks of BAC transgenesis compared to other techniques such as knock-in and CRISPR/Cas9 technologies. The review emphasizes the applications of BAC transgenic mice in various disciplines, including neuroscience, immunology, drug metabolism, and disease modeling. Additionally, we address crucial aspects of generating and analyzing BAC transgenic mice, such as position effects, copy number variations, and strategies to mitigate these challenges. Despite certain limitations, humanized BAC transgenic mice have proven to be invaluable tools for studying the pathogenesis of human diseases, drug development, and understanding intricate gene regulatory mechanisms. This review discusses current topics on BAC transgenic mice and their evolving significance in biomedical research.

Pregnancy-related factors induce immune tolerance through regulation of sCD83 release

A well-balanced maternal immune system is crucial to maintain fetal tolerance in case of infections during pregnancy. Immune adaptations include an increased secretion of soluble mediators to protect the semi-allogeneic fetus from excessive pro-inflammatory response. B lymphocytes acquire a higher capacity to express CD83 and secrete soluble CD83 (sCD83) upon exposure to bacteria-derived components such as LPS. CD83 possesses immune modulatory functions and shows a promising therapeutic potential against inflammatory conditions. The administration of sCD83 to pregnant mice reduces LPS-induced abortion rates. The increased CD83 expression by endometrial B cells as compared to peripheral blood B cells suggests its modulatory role in the fetal tolerance, especially in the context of infection. We postulate that in pregnancy, CD83 expression and release is controlled by pregnancy-related hormones. The intra- and extracellular expression of CD83 in leukocytes from peripheral blood or decidua basalis and parietalis at term were analyzed by flow cytometry. After treatment with pregnancy-related hormones and LPS, ELISA and qPCR were performed to study sCD83 release and CD83 gene expression, respectively. Cleavage prediction analysis was used to find potential proteases targeting CD83. Expression of selected proteases was analyzed by ELISA. Higher levels of CD83 were found in CD11c+ dendritic cells, CD3+ T cells and CD19+ B cells from decidua basalis and decidua parietalis after LPS-stimulation in vitro. An increase of intracellular expression of CD83 was also detected in CD19+ B cells from both compartments. Stimulated B cells displayed significantly higher percentages of CD83+ cells than dendritic cells and T cells from decidua basalis and peripheral blood. Treatment of B lymphocytes with pregnancy-related molecules (E2, P4, TGF-β1 and hCG) enhanced the LPS-mediated increase of CD83 expression, while dexamethasone led to a reduction. Similarly, the release of sCD83 was increased under TGF-β1 treatment but decreased upon dexamethasone stimulation. Finally, we found that the hormonal regulation of CD83 expression is likely a result from a balance between gene transcription from CD83 and the modulation of the metalloproteinase MMP-7. Thus, data supports and complements our previous murine studies on hormonal regulation of CD83 expression, reinforcing its immunomodulatory relevance in anti-bacterial responses during pregnancy.

HNF4α, SP1 and c-myc are master regulators of CNS autoimmunity

Hepatocyte nuclear factor 4 α (HNF4α), a transcription factor (TF) essential for embryonic development, has been recently shown to regulate the expression of inflammatory genes. To characterize HNF4a function in immunity, we measured the effect of HNF4α antagonists on immune cell responses in vitro and in vivo. HNF4α blockade reduced immune activation in vitro and disease severity in the experimental model of multiple sclerosis (MS). Network biology studies of human immune transcriptomes unraveled HNF4α together with SP1 and c-myc as master TF regulating differential expression at all MS stages. TF expression was boosted by immune cell activation, regulated by environmental MS risk factors and higher in MS immune cells compared to controls. Administration of compounds targeting TF expression or function demonstrated non-synergic, interdependent transcriptional control of CNS autoimmunity in vitro and in vivo. Collectively, we identified a coregulatory transcriptional network sustaining neuroinflammation and representing an attractive therapeutic target for MS and other inflammatory disorders.

CD83 Regulates the Immune Responses in Inflammatory Disorders

Activating the immune system plays an important role in maintaining physiological homeostasis and defending the body against harmful infections. However, abnormalities in the immune response can lead to various immunopathological responses and severe inflammation. The activation of dendritic cells (DCs) can influence immunological responses by promoting the differentiation of T cells into various functional subtypes crucial for the eradication of pathogens. CD83 is a molecule known to be expressed on mature DCs, activated B cells, and T cells. Two isotypes of CD83, a membrane-bound form and a soluble form, are subjects of extensive scientific research. It has been suggested that CD83 is not only a ubiquitous co-stimulatory molecule but also a crucial player in monitoring and resolving inflammatory reactions. Although CD83 has been involved in immunological responses, its functions in autoimmune diseases and effects on pathogen immune evasion remain unclear. Herein, we outline current immunological findings and the proposed function of CD83 in inflammatory disorders.

Crosstalk between dendritic cells and regulatory T cells: Protective effect and therapeutic potential in multiple sclerosis

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system related to autoimmunity and is characterized by demyelination, neuroinflammation, and neurodegeneration. Cell therapies mediated by dendritic cells (DCs) and regulatory T cells (Tregs) have gradually become accumulating focusing in MS, and the protective crosstalk mechanisms between DCs and Tregs provide the basis for the efficacy of treatment regimens. In MS and its animal model experimental autoimmune encephalomyelitis, DCs communicate with Tregs to form immune synapses and complete a variety of complex interactions to counteract the unbalanced immune tolerance. Through different co-stimulatory/inhibitory molecules, cytokines, and metabolic enzymes, DCs regulate the proliferation, differentiation and function of Tregs. On the other hand, Tregs inhibit the mature state and antigen presentation ability of DCs, ultimately improving immune tolerance. In this review, we summarized the pivotal immune targets in the interaction between DCs and Tregs, and elucidated the protective mechanisms of DC-Treg cell crosstalk in MS, finally interpreted the complex cell interplay in the manner of inhibitory feedback loops to explore novel therapeutic directions for MS.

Tilting the Balance: Therapeutic Prospects of CD83 as a Checkpoint Molecule Controlling Resolution of Inflammation

Chronic inflammatory diseases and transplant rejection represent major challenges for modern health care. Thus, identification of immune checkpoints that contribute to resolution of inflammation is key to developing novel therapeutic agents for those conditions. In recent years, the CD83 (cluster of differentiation 83) protein has emerged as an interesting potential candidate for such a "pro-resolution" therapy. This molecule occurs in a membrane-bound and a soluble isoform (mCD83 and sCD83, respectively), both of which are involved in resolution of inflammation. Originally described as a maturation marker on dendritic cells (DCs), mCD83 is also expressed by activated B and T cells as well as regulatory T cells (Tregs) and controls turnover of MHC II molecules in the thymus, and thereby positive selection of CD4+ T cells. Additionally, it serves to confine overshooting (auto-)immune responses. Consequently, animals with a conditional deletion of CD83 in DCs or regulatory T cells suffer from impaired resolution of inflammation. Pro-resolving effects of sCD83 became evident in pre-clinical autoimmune and transplantation models, where application of sCD83 reduced disease symptoms and enhanced allograft survival, respectively. Here, we summarize recent advances regarding CD83-mediated resolution of inflammatory responses, its binding partners as well as induced signaling pathways, and emphasize its therapeutic potential for future clinical trials.

Intestinal Epithelial Cell-Derived CD83 Contributes to Regulatory T-Cell Generation and Inhibition of Food Allergy

The mechanism of generation of antigen-specific regulatory T cells (Treg) is not fully understood yet. This study aimed to investigate the role of intestinal epithelial cell (IEC)-derived CD83 in the Treg generation in the intestine. In this study, the role of CD83 in the generation of Tregs was assessed in a cell-culture model and a food allergy (FA) mouse model. We found that mouse IECs expressed CD83; its levels were markedly lower in sensitized mice. Mice with CD83-deficient IECs failed to induce Tregs in the intestine. CD83 promoted the transforming growth factor-β-inducible early gene 1 (TIEG1) expression in CD4+ T cells. Toll-like receptor 4 (TLR4)/myeloid differentiation protein-2 (MD-2) complex mediated the effects of CD83 on the expression of TIEG1. Activation of the CD83/TLR4/MD-2/TIEG1 promoted the Treg generation. Concomitant administration of CD83 and specific antigens, but not either one alone, efficiently inhibited experimental FA via inducing the Treg generation in the intestine. In Conclusion, IEC expresses CD83 that is low in sensitized mice. Concomitant administration of CD83 and specific antigens efficiently inhibits FA in a murine model via inducing Tregs in the intestine. The data suggest that CD83 has translation potential in the treatment of FA.

Integrin α4β1/VCAM-1 Interaction Evokes Dynamic Cell Aggregation Between Immune Cells and Human Lung Microvascular Endothelial Cells at Infectious Hemolysis

Bacterial and viral infection is a common cause of pneumonia, respiratory failure, and even acute respiratory distress syndrome. Increasing evidence indicates that red blood cells (RBCs) may contribute to immune response and inflammation. However, the precise molecular mechanisms that link RBC and hemolysis to the development and progression of inflammatory pathologies are not entirely understood. In this study, we used bacterial endotoxin, lipopolysaccharide (LPS), to mimic an infectious hemolysis and found that RBCs dynamically regulated cell aggregation between immune cells and human lung microvascular endothelial cells (HLMVEC). When RBCs were treated with LPS, integrin α4β1 was increased and was accompanied by cytokines and chemokines release (TNF-α, IL-1β, IL-6, IL-8, IFN-γ, CXCL12, CCL5, CCL7 and CCL4). Upon α4β1 elevation, RBCs not only facilitated mature monocyte derived dendritic cell (mo-DCs) adhesion but also promoted HLMVEC aggregation. Furthermore, co-culture of the supernatant of LPS pre-treated RBCs with mo-DCs could promote naïve CD4 T cell proliferation. Notably, the filtered culture from LPS-lysed RBCs further promoted mo-DCs migration in a concentration dependent manner. From a therapeutic perspective, cyclic peptide inhibitor of integrin α4β1 combined with methylprednisolone (α4β1/Methrol) remarkably blocked RBCs aggregation to mo-DCs, HLMVEC, or mo-DCs and HLMVEC mixture. Moreover, α4β1/Methrol dramatically reduced mo-DCs migration up-regulated glucocorticoid-induced leucine zipper in mo-DCs, and ultimately reversed immune cell dysfunction induced by hemolysis. Taken together, these results indicate that integrin α4β1 on RBCs could mediate cell-cell interaction for adaptive immunity through influencing cell adhesion, migration, and T cell proliferation.

T and B Lymphocyte Transcriptional States Differentiate between Sensitized and Unsensitized Individuals in Alpha-Gal Syndrome

The mechanisms of pathogenesis driving alpha-gal syndrome (AGS) are not fully understood. Differences in immune gene expression between AGS individuals and non-allergic controls may illuminate molecular pathways and targets critical for AGS development. We performed immune expression profiling with RNA from the peripheral blood mononuclear cells (PBMCs) of seven controls, 15 AGS participants, and two participants sensitized but not allergic to alpha-gal using the NanoString nCounter PanCancer immune profiling panel, which includes 770 genes from 14 different cell types. The top differentially expressed genes (DEG) between AGS subjects and controls included transcription factors regulating immune gene expression, such as the NFκB pathway (NFKBIA, NFKB2, REL), antigen presentation molecules, type 2/allergic immune responses, itch, and allergic dermatitis. The differential expression of genes linked to T and B cell function was also identified, including transcription factor BCL-6, markers of antigen experience (CD44) and memory (CD27), chemokine receptors (CXCR3, CXCR6), and regulators of B-cell proliferation, cell cycle entry and immunoglobulin production (CD70). The PBMCs from AGS subjects also had increased TNF and IFN-gamma mRNA expression compared to controls. AGS is associated with a distinct gene expression profile in circulating PBMCs. DEGs related to antigen presentation, antigen-experienced T-cells, and type 2 immune responses may promote the development of alpha-gal specific IgE and the maintenance of AGS.

Endogenous CD83 Expression in CD4+ Conventional T Cells Controls Inflammatory Immune Responses

The glycoprotein CD83 is known to be expressed by different immune cells including activated CD4+Foxp3+ regulatory T cells (Tregs) and CD4+Foxp3- conventional T cells. However, the physiological function of endogenous CD83 in CD4+ T cell subsets is still unclear. In this study, we have generated a new CD83flox mouse line on BALB/c background, allowing for specific ablation of CD83 in T cells upon breeding with CD4-cre mice. Tregs from CD83flox/flox/CD4-cretg/wt mice had similar suppressive activity as Tregs from CD83flox/flox/CD4-crewt/wt wild-type littermates, suggesting that endogenous CD83 expression is dispensable for the inhibitory capacity of Tregs. However, CD83-deficient CD4+ conventional T cells showed elevated proliferation and IFN-γ secretion as well as an enhanced capacity to differentiate into Th1 cells and Th17 cells upon stimulation in vitro. T cell-specific ablation of CD83 expression resulted in aggravated contact hypersensitivity reaction accompanied by enhanced CD4+ T cell activation. Moreover, adoptive transfer of CD4+CD45RBhigh T cells from CD83flox/flox/CD4-cretg /wt mice into Rag2-deficient mice elicited more severe colitis associated with increased serum concentrations of IL-12 and elevated CD40 expression on CD11c+ dendritic cells (DCs). Strikingly, DCs from BALB/c mice cocultured with CD83-deficient CD4+ conventional T cells showed enhanced CD40 expression and IL-12 secretion compared with DCs cocultured with CD4+ conventional T cells from CD83flox/flox/CD4-crewt/wt wild-type mice. In summary, these results indicate that endogenous CD83 expression in CD4+ conventional T cells plays a crucial role in controlling CD4+ T cell responses, at least in part, by regulating the activity of CD11c+ DCs.

The CD83 Molecule - An Important Immune Checkpoint

The CD83 molecule has been identified to be expressed on numerous activated immune cells, including B and T lymphocytes, monocytes, dendritic cells, microglia, and neutrophils. Both isoforms of CD83, the membrane-bound as well as its soluble form are topic of intensive research investigations. Several studies revealed that CD83 is not a typical co-stimulatory molecule, but rather plays a critical role in controlling and resolving immune responses. Moreover, CD83 is an essential factor during the differentiation of T and B lymphocytes, and the development and maintenance of tolerance. The identification of its interaction partners as well as signaling pathways have been an enigma for the last decades. Here, we report the latest data on the expression, structure, and the signaling partners of CD83. In addition, we review the regulatory functions of CD83, including its striking modulatory potential to maintain the balance between tolerance versus inflammation during homeostasis or pathologies. These immunomodulatory properties of CD83 emphasize its exceptional therapeutic potential, which has been documented in specific preclinical disease models.