Role of thymus in health and disease

The thymus is a primary lymphoid organ, essential for the development of T-cells that will protect from invading pathogens, immune disorders, and cancer. The thymus decreases in size and cellularity with age referred to as thymus involution or atrophy. This involution causes decreased T-cell development and decreased naive T-cell emigration to the periphery, increased proportion of memory T cells, and a restricted, altered T-cell receptor (TCR) repertoire. The changes in composition and function of the circulating T cell pool as a result of thymic involution led to increased susceptibility to infectious diseases including the recent COVID and a higher risk for autoimmune disorders and cancers. Thymic involution consisting of both structural and functional loss of the thymus has a deleterious effect on T cell development, T cell selection, and tolerance. The mechanisms which act on the structural (cortex and medulla) matrix of the thymus, the gradual accumulation of genetic mutations, and altered gene expressions may lead to immunosenescence as a result of thymus involution. Understanding the molecular mechanisms behind thymic involution is critical for identifying diagnostic biomarkers and targets for treatment help to develop strategies to mitigate thymic involution-associated complications. This review is focused on the consequences of thymic involution in infections, immune disorders, and diseases, identifying potential checkpoints and potential approaches to sustain or restore the function of the thymus particularly in elderly and immune-compromised individuals.

Short-Term Relocation Stress-Induced Hematological and Immunological Changes in Saimiri boliviensis boliviensis

Nonhuman primates are frequently transported to a new location or temporarily relocated within their colony. Both transportation and relocation expose animals to new environments, causing them to undergo a stress response (before adapting). In our NHP colony, the mentioned situations are not infrequent for many reasons, including maintenance. The objective of this study was to determine whether abrupt changes consisting of relocation, housing, separation, and grouping could influence hematological and immunological parameters and thereby functional activity. The current study used squirrel monkeys as a model to investigate the stress-inducing effects of relocation within a facility, while animals acclimated to new situations (physical, housing). A detailed blood analysis revealed significant changes in lymphocytes, triglycerides, total protein, creatinine, and ALT. Flow cytometric analysis of peripheral blood showed reduction in CD3+, CD4+, and CD8+ T cells and monocytes, while B cells and natural killer (NK) cells changed with relocation. Simultaneously, changes in functional activity of immune cells altered proliferative responses and as shown by ELISpot (IFN γ). Though the parameters studied are not affected as severely as those in animals transported by road or air, stress responses induced by intrafacility relocation are significant and worth consideration. Our findings indicate that squirrel monkeys mimic the features seen in humans exposed to social stressors and may serve an important model for understanding the mechanisms of stress-induced immune dysfunction in humans.

Immune respones against Trypanosoma cruzi infection by oral route in cynomolgus macaques (Macaca fascicularis)

American Trypanosomiasis is an important neglected reemerging tropical parasitism, infecting about 8 million people worldwide. Its agent, Trypanosoma cruzi, exhibits multiple mechanisms to evade the host immune response and infect host cells. An important immune evasion strategy of T. cruzi infective stages is its capacity to inhibit the complement system activation on the parasite surface, avoiding opsonizing, immune stimulating and lytic effects. Eight male M. fascicularis between 8 and 10 years of age of Chinese origin were infected through oral administration of T. cruzi-infected triatomine bugs and followed over 6 weeks. The purpose of this study was to define cellular immunological responses in T. Cruzi challenged M. fascicularis. We measured immunofluorescent staining and multifunctional T. cruzi antigen specific T-cell responses in experimental infected M. fascicularis. Significant increases in the CD4+ T-cell population and polyfunctional T cell responses were observed in all experimental-infected animals compared with the uninfected time points. We observed a decrease in absolute number of lymphocytes, T cells and T cell subsets, in early phase of infection but recovered in later period. T. cruzi antigen specific IFN-g and IL-12p40 ELISPOT showed no significant infection specific responses during the study period. Circulating cytokines measurement in plasma revealed a significant increase IFN-g and IL-1ra during infection period. In conclusion, our present findings provide the first evidence demonstrating the Trypanosoma cruzi infection by oral route.

Plasmacytoid dendritic cells (pDCs) and IFN- production in aged squirrel monkeys (Saimiri boliviensis boliviensis) stimulated with Class C CpG Oligodeoxynucleotides

Synthetic CpG oligodeoxynucleotides (ODNs) with defined CpG motifs and immunomodulatory properties signal through an endosomal membrane-based type of pattern recognition receptor (PRR), the Toll-like receptor 9 (TLR9), that has been identified in dendritic cells (DCs), B cells, and other human immune cell types. CpG-ODNs influence several signaling pathways, leading to cytokine production in many mammalian species that make CpG ODNs suitable as therapeutic interventions in a variety of human disease conditions. The squirrel monkey (SQM), a well-established New World non-human primate (NHP) model is known to be used for studying various diseases such as Alzheimer’s disease (AD), malaria, and transmissible spongiform encephalopathies (Creutzfeldt-Jacob disease). In the present study, we generated the first report of immunoregulatory activity of class C CpG-ODN in aged squirrel monkey. CpG-ODN exhibits very potent effects on squirrel monkey immune cells by inducing IFN-γ/IFN-α from peripheral blood mononuclear cells and demonstrates accelerated kinetics of activity. In addition, class C CpG-ODN specifically activates pDCs to undergo maturation and secrete cytokines, including high levels of IFN-α. To best to our knowledge, this is the first documentation describing immune status in squirrel monkeys immunized with C class CpG-ODN by concentrating on lymphocyte surface antigen expression and function. Overall, our findings provide critical data regarding the immunomodulatory potential of CpG-ODN in this NHP model allowing for future therapeutic trials of innate immunity stimulation via TLR9 agonists for diverse indications including AD therapeutics.

Class C CpG Oligodeoxynucleotide Immunomodulatory Response in Aged Squirrel Monkey (Saimiri Boliviensis Boliviensis)

One means of stimulating the mammalian innate immune system is via Toll-like receptor 9 (TLR9) being exposed to unmethylated cytosine-phosphate-guanine (CpG) DNA, also known as pathogen-associated molecular patterns (PAMPs) of microbial origin. Synthetic CpG oligodeoxynucleotides (ODNs) with defined CpG motifs possess broad immunostimulatory properties that make CpG ODNs suitable as therapeutic interventions in a variety of human disease conditions, including Alzheimer's disease (AD). Rodent models are often used to preclinically test the effectiveness of CpG ODN therapeutic agents for AD and other disorders. However, the translatability of findings in such models is limited due to the significant difference of the expression of TLR9 between primates and rodents. The squirrel monkey (SQM), a New World non-human primate (NHP), is known to be phylogenetically proximate to humans, and develops extensive age-dependent cerebral amyloid angiopathy (CAA), a key pathological feature of AD. Hence, this model is currently being used to test AD therapeutics. In the present study, we conducted the first examination of Class C CpG ODN's immunomodulatory role in elderly SQMs. We documented the effectiveness of CpG ODN to trigger an immune response in an aged cohort whose immune system is senescent. The specific immune response patterns detected here closely resembled CpG ODN-induced immunostimulatory patterns observed in prior human studies. Overall, our findings provide critical data regarding the immunomodulatory potential of CpG ODN in this NHP model, allowing for future translational studies of innate immunity stimulation via TLR9 agonists for diverse indications, including AD therapeutics.

Comparative Analysis of Cellular Immune Responses in Conventional and SPF Olive Baboons (Papio anubis)

Olive baboons (P. anubis) have provided a useful model of human diseases and conditions, including cardiac, respiratory, and infectious diseases; diabetes; and involving genetics, immunology, aging, and xenotransplantation. The development of a immunologically defined SPF baboons has advanced research further, especially for studies involving the immune system and immunosuppression. In this study, we compare normal immunologic changes of PBMC subsets, and their function in age-matched conventional and SPF baboons. Our results revealed that both groups have comparable numbers of different lymphocyte subsets, but phenotypic differences in central and effector memory T-cell subsets are more pronounced in CD4+ T cells. Despite equal proportions of CD3+ T cells among the conventional and SPF baboons, PBMC from the conventional group showed greater proliferative responses to phytohemagglutinin and pokeweed mitogen and higher numbers of IFNγ-producing cells after stimulation with concanavalin A or pokeweed mitogen, whereas plasma levels of the inflammatory cytokine TNFα were significantly higher in SPF baboons. Exposure of PBMC from conventional baboons to various Toll-like (TLR) ligands, including TLR3, TLR4, and TLR8, yielded increased numbers of IFNγ producing cells, whereas PBMC from SPF baboons stimulated with TLR5 or TLR6 ligand had more IFNγ-producing cells. These findings suggest that although lymphocyte subsets share many phenotypic and functional similarities in conventional and SPF baboons, specific differences in the immune function of lymphocytes could differentially influence the quality and quantity of their innate and adaptive immune responses. These differences should be considered in interpreting experimental outcomes, specifically in studies measuring immunologic endpoints.

Effects of Transportation and Relocation on Immunologic Measures in Cynomolgus Macaques (Macaca fascicularis)

NHP are a small, but critical, portion of the animals studied in research laboratories. Many NHP are imported or raised at one facility and subsequently moved to another facility for research purposes. To improve our understanding of the effects of transportation and relocation on the NHP immune system, to minimize potential confounds associated with relocation, and to maximize study validity, we examined the phenotype and function of PBMC in cynomolgus macaques (Macaca fascicularis) that were transported approximately 200 miles by road from one facility to another. We evaluated the phenotype of lymphocyte subsets through flow cytometry, mitogen-specific immune responses of PBMC in vitro, and plasma levels of circulating cytokines before transportation, at approximately 24 h after arrival (day 2), and after 30 d of acclimation. Analyses of blood samples revealed that the CD3+ and CD4+ T-cell counts increased significantly, whereas NK+, NKT, and CD14+ CD16+ nonclassical monocyte subsets were decreased significantly on day 2 after relocation compared with baseline. We also noted significantly increased immune cell function as indicated by mitogen-specific proliferative responses and by IFNγ levels on day 2 compared with baseline. After 30 d of acclimation, peripheral blood CD4+ T-cells and monocyte counts were higher than baseline, whereas B-cell numbers were lower. The mitogen-induced responses to LPS and IFNγ production after stimulation with pokeweed mitogen or phytohemagglutinin remained significantly different from baseline. In conclusion, the effects of transportation and relocation on immune parameters in cynomolgus monkeys are significant and do not fully return to baseline values even after 30 d of acclimation.

Cellular immune responses in peripheral blood lymphocytes of Giardia infected squirrel monkey (Saimiri boliviensis boliviensis) treated with Fenbendazole

Cellular immune responses were tested to determine the effect of fenbendazole on the function of lymphocytes from Bolivian squirrel monkeys (Samiri boliviensis boliviensis). Giardia-infected squirrel monkeys were treated with commercially available fenbendazole (FBZ)-medicated monkey chow. Immune responses were compared between historical controls (Giardia naïve, untreated with FBZ (control animals)) and Giardia-infected, FBZ-treated squirrel monkeys (study animals). Peripheral blood lymphocytes from study monkeys had significantly lower stimulation indices compared to control animals when cultured in vitro with concanavalin A (Con A) (p<0.0001), phytohaemagglutinin (PHA) (p<0.0001) and lipopolysaccharide (LPS) (p<0.0001). PBMCs were also analyzed for IFN-γ producing cells in response to stimulation with Con A, PHA, PWM, and LPS by the cytokine ELISPOT assay. Significantly higher responses to Con A- (p<0.0001), and PHA- (p<0.001) stimulated cultures from Giardia-infected and fenbendazole treated compared to controls. Flow cytometric analysis for expression of cell surface markers revealed a significant increase in B- and NKT-lymphocytes and significant decrease in CD14+CD16+ monocytes after FBZ treatment. Also, circulating plasma cytokines IFN-γ, TNF-α, IL-12p40, IL-1β, IL-10, IL-13, IL-1ra, IL-6 and IL-4 were significantly decreased after FBZ treatment. Comparison of hematologic parameters between controls and FBZ-treated squirrel monkeys revealed significantly lower numbers of total leukocytes, neutrophils, monocytes, and eosinophils compared to controls. However, erythrocyte indices (red cell count, hemoglobin and hematocrit were significantly higher in FBZ-treated monkeys. Our findings suggest that fenbendazole treatment may alter sensitive immune and molecular measures of inflammation. Postponing the experimental use of squirrel monkeys until at least 6 weeks after FBZ treatment should be considered.

Identification and functional analysis of NKp46+ natural killer cells from peripheral blood of squirrel (Saimiri sps.) and owl monkey (Aotus sps.)

Natural Killer (NK) cells as minor subsets of peripheral blood lymphocytes (PBL) are innate in nature to clear invading pathogens and tumor cells. Small rodent species to nonhuman primates and humans, immune systems consist of a spectrum of NK cell subsets with phenotype and functional diversity. This study examined NK cell subsets and expression of NKp46 in squirrel and owl monkeys, which are both New World primate species. Squirrel and owl monkeys are recommended by the World Health Organization as excellent experimental models for studies of malaria infection due to their susceptibility to some of the same strains that cause disease in humans and endemic viruses that are analogues of opportunistic human viruses. NK cells were identified from CD3 negative lymphocytes and sub-phenotyped by CD16 and CD8 expression, to classify CD8+ and CD8− NK cells and absolute numbers in peripheral blood were compared. Analysis of expression of NCR (Natural Cytotoxicity Receptors) proteins, NKp30 and NKp46 showed that NK cells from NHP had preferential expression of NKp46 over NKp30 and expression is mostly restricted to subset of CD8+ NK cells. Peripheral blood lymphocytes, enriched based on NKp46 expression, were further phenotyped as classic CD3−CD16+CD8+NK cells. Functional analysis of enriched cells was focused to verify whether subsets differ in cytolitic and/or “innate” in nature and to correlate with NCR protein expression. Enriched NK cells were co-cultured for stimulation with standard target cells including tumor cells and analyzed for cytokine production. The potential plasticity of peripheral blood NK cells in NHP based on steady state and/or inflammatory/pathogenic status of species will be analyzed and discussed.

Effects of transportation, relocation, and acclimation on phenotypes and functional characteristics of peripheral blood lymphocytes in rhesus monkeys (Macaca mulatta)

Nonhuman primates from domestic sources constitute a small, but critical, proportion of animals studied in research laboratories. Many of these nonhuman primates are raised at one facility and subsequently transported/relocated to another facility for research purposes. We examined the effects of transport, relocation, and acclimation on the phenotype and function of peripheral blood mononuclear cells (PBMCs) in a group of rhesus monkeys that were transported by road for approximately 21 hours from one facility to another. Using a panel of human antibodies and a set of standardized human immune assays, we evaluated the phenotype of lymphocyte subsets by flow, mitogen-specific immune responses of PBMCs in vitro, and levels of circulating cytokines and cortisol in plasma at various time points including immediately before transport, immediately upon arrival, and after approximately 30 days of acclimation. Analyses of blood samples revealed that CD3+ T-cell and CD20+ B-cell populations had decreased significantly immediately after relocation but had recovered within 30 days after arrival at the new facility. Similarly, circulating cortisol and cytokine levels in plasma were significantly higher immediately after relocation; and by the 30-day time point, these differences were no longer significant. However, immune assays of PBMCs indicated that mitogen-specific responses for proliferation, interferon γ (IFN-γ), and perforin were significantly higher after relocation and 30 days of acclimation. These findings have implications on the research participation of transported and relocated nonhuman primates in immunologic research studies, suggesting that 30 days is not sufficient to ensure return to baseline immune homeostasis. These data should be considered when planning research studies in order to minimize potential confounding factors associated with relocation and to maximize study validity.

Phenotypic and Functional Characterization of Peripheral Blood Lymphocytes from Various Age- and Sex-Specific Groups of Owl Monkeys (Aotus nancymaae)

Owl monkeys (Aotus nancymaae) are New World NHP that serve an important role in vaccine development and as a model for human disease conditions such as malaria. Despite the past contributions of this animal model, limited information is available about the phenotype and functional properties of peripheral blood lymphocytes in reference to sex and age. Using a panel of human antibodies and a set of standardized human immune assays, we identified and characterized various peripheral blood lymphocyte subsets, evaluated the immune functions of T cells, and analyzed cytokines relative to sex and age in healthy owl monkeys. We noted age- and sex-dependent changes in CD28+ (an essential T cell costimulatory molecule) and CD95+ (an apoptotic surface marker) T cells and various levels of cytokines in the plasma. In immune assays of freshly isolated peripheral blood mononuclear cells, IFNγ and perforin responses were significantly higher in female than in male monkeys and in young adults than in juvenile and geriatric groups, despite similar lymphocyte (particularly T cell) populations in these groups. Our current findings may be useful in exploring Aotus monkeys as a model system for the study of aging, susceptibility to infectious diseases, and age-associated differences in vaccine efficacy, and other challenges particular to pediatric and geriatric patients.

TLR4-based IL-8 reporter cell line as a tool for screening of the LPS-mediated immunomodulators to control TLR4 signaling pathway. (P3305)

The lipopolysaccharide (LPS) receptor complex of TLR4, MD-2 and CD14 plays an important role in sensing LPS-mediated immune signals, which provide immediate host protection and stimulate the host immune responses. Despite the fact that TLR4-mediated innate immune signals are required to combat invading pathogens, when signaling is not well regulated, uncontrolled activation can result in the disruption of host homeostasis leading to chronic inflammation and septic shock. Hence it is crucial to develop an assay system that can identify immunomodulators to control TLR4 signaling pathway. Since IL-8 is a major cytokine induced by TLR4, we developed the reporter cell line which stably expresses TLR4, MD-2 and CD14 proteins as well as an optimized Renilla luciferase reporter gene under the transcriptional control of IL-8 promoter. Functional activity of the cell line was evaluated by LPS dose response, TLR4 antagonist test and IL-8 induction suppressor test. The LPS EC50 of 4.3 ng/ml, TLR4 inhibitory peptide IC50 of 14.85 uM and an IL-8 induction suppressor, curcumin IC50 of 15.29 uM against the cell line were assessed. Using this cell line, a series of natural compounds was successfully screened for TLR4 signaling modulators, among which several compounds were identified as potential TLR4 signaling modulators. Taken together, it is proposed that this reporter cell line can be used as a tool for analyzing TLR4 signaling pathway as well as screening of TLR4 signaling modulators.

Characterization of a small molecule compound VPR-66 as an inverse agonist for ROR proteins (P5167)

Retinoic Acid Receptor (RAR)-Related Orphan Receptors RORα, RORγ and RORγt are key transcription factors required for differentiation of naive CD4+ helper cells into Th17 cells that play an important role in driving autoimmune and inflammatory diseases by secretion of IL-17 and other pro-inflammatory cytokines. Recently development of the Th17 immunomodulators as potential therapeutics for autoimmune diseases has been focused on ROR proteins to regulate differentiation and IL-17 production of Th17 cells. We designed a small molecule compound VPR-66 via the molecular modeling study, which is hypothesized to bind to the ligand-binding domain (LBD) of ROR proteins. VPR-66 was characterized by two different cell-based reporter assays, in which the LBD or full-length of ROR proteins were utilized. In the LBD-based assay, VPR-66 selectively suppressed the RORα and RORγt LBD-mediated transcriptional activity but showed little or no effects on VP16 control protein- or RARα LBD-mediated transcriptional activity. Similarly, in the full-length ROR-based assay, VPR-66 significantly inhibited RORγ- or RORγt-induced IL-17A promoter activity while VPR-66 did not affect the promoter activity in the absence of ROR protein expression. Taken together, it is proposed that VPR-66 acts as an inverse agonist specific for ROR proteins and its binding to ROR proteins interferes with transcriptional complex formation for IL-17 induction.

Development of inhibitory peptide to control TLR9 signaling pathway. (180.17)

Toll-like receptors (TLRs) play an important role in sensing microbial molecules. Upon recognition of microbial components, TLRs quickly engage with their adaptors and initiate innate immune signals by sequentially recruiting downstream signaling mediators, which provide immediate host protection and stimulate the host’s adaptive immune response. Despite the fact that TLR-mediated innate immune signals are required to combat invading pathogens, when signaling is not well regulated, uncontrolled activation can result in the disruption of host homeostasis leading to chronic inflammation and septic shock. Although there are naturally occurring negative regulators of TLR signaling that function as part of cell homeostasis, these are not adequate in all situations. Hence development of a targeted therapeutic means or molecule that can effectively control TLR-mediated chronic inflammation is crucial. In response to this, we have developed a synthetic peptide based on a CpG-binding motif in the extracellular domain of TLR9, which can inhibit TLR9 signaling. Using TLR9/NF-κB/SEAPorter™ HEK 293 cell line, the inhibitory peptide was validated together with a control peptide in which conserved residues were modified. The inhibitory peptide significantly suppressed CpG-mediated TLR9 activation while the control peptide did not affect TLR9 activation. Test of another peptide with differential residue modification further revealed the key residues involved in CpG-mediated TLR9 activation.

Development of IL-17A promoter-based reporter cell line and activation of the cell line by exogenous expression of RORγ and RORγt. (59.12)

As one of the six known IL-17 family members, IL-17A is a proinflammatory cytokine secreted by innate and adaptive immune cells. Especially IL-17A has been characterized as a key cytokine produced in a new CD4+ T helper subset, Th17 cells, which play an important role in host defense against specific pathogens. Effect of IL-17A is also implicated with pathogenic role of Th17 cells in autoimmunity and the chronic activation of IL-17-producing T helper cells can lead to autoimmune diseases. Indeed, increased levels of IL-17 have been observed in patients with autoimmune diseases including rheumatoid arthritis, multiple sclerosis, inflammatory bowel disease and psoriasis as shown by researchers. Hence development of a targeted therapeutic means or molecule that can effectively control IL-17 induction is crucial to prevent the initiation of IL-17-producing cell-mediated autoimmune diseases. In response to this, we have developed the IL-17A Prom/LUCPorter™ HEK 293 cell line, in which Renilla luciferase reporter gene is under control of the inducible IL-17A promoter. This cell line has been validated by exogenous expression of RORγ or RORγt construct, which can induce the IL-17A promoter activity leading to expression of luciferase reporter protein. This cell line is suitable for screening of antagonists for IL-17A induction which can be utilized as the therapeutic target molecules to control IL-17-producing cells.

Characterization of a human toll-like receptor 3 antibody designed to block ligand binding and ligand mediated signaling (180.16)

Toll-like receptors (TLRs) play key roles during pathogen invasion to initiate innate immune responses. Toll-like receptor 3 (TLR3) recognizes double-stranded RNA (microbial and endogenous) and transmits signals to activate NF-kappa B. TLR3 is restricted to acidic pH+ intracellular compartments of innate immune cells (viz immature DC). Ligand binding and formation of multimeric signal complexes, to activate down-stream signaling, are facilitated by acidic pH in these compartments. Mutational and co-crystallization studies determined the interaction of TLR3 & ligand binding at the molecular level and also individual residues important in ligand recognition and signal transduction. Besides, neutralizing antibodies were utilized as tools for better understanding of ligand binding and TLR3 signaling. In the present study, we report results of a TLR3 antibody which blocks ligand (poly IC) binding and its' effect on functional activity. We tested multiple TLR3 antibodies, generated through use of synthetic peptides designed to include various regions of protein and also the residues playing important role in ligand binding. The binding and blocking (ligand) activities were analyzed by flow cytometry using TLR3 transfectant cells in presence/absence of poly IC. We also tested blocking activity in a functional assay by measuring secreted alkaline phosphatase (SEAP) in cultures of TLR3-NF-kB-SEAP co-transfectants stimulated wih poly IC in the presence of antibody.

Flow cytometry based analysis for subsets of Plasmacytoid Dendritic Cells (pDC) from human PBMC (100.31)

Dendritic cells are a heterogeneous group of antigen presenting cells that link innate and adaptive immunity. In mice and humans, subsets of DC have been identified, based on origin, location, differentiation, phenotype and functions. Newly identified markers, availability of mAb(s) and advanced flow-cytometry techniques have helped in enumerating existence of such subsets. Plasmacytoid dendritic cells (pDC) are peripheral blood DC subsets, which produce IFN (Type I) and are vital for anti-viral immunity. pDC exist in small numbers (~0.1-0.5%) in peripheral blood and their phenotype analysis by flow, includes CD123 and HLADR expression on lineage negative populations of PBMC. Recently, pDC were shown to play important roles (besides anti-viral) in other human diseases such as lupus and psoriasis but it is not known if distinct subsets are associated. In the present study we used three markers viz. CD123, BDCA-2 and ILT7 (newly identified) to analyze potential subsets of pDC. As Type I IFN producers, pDC express intracellular toll-like receptors TLR7 and TLR9 and our analysis extends to include whether these subsets differ in TLR expression, particularly focusing on TLRs playing an important role in innate-IFN (Type I) production. In order to understand the role of pDC (subsets) in induction of anti-immune responses towards other microbes, expression of non-specific markers such as Dectin-2 and TLR 10 were also tested using newly available mAb(s).

Development of functionally active recombinant form of mouse IL-35 (57.11)

As a novel heterodimeric cytokine and one of the IL-12 family members, IL-35 is composed of IL-12p35 subunit and Epstein-Barr virus-induced gene 3 (EBI3) protein. IL-35 is known to play an essential role in immune regulation of the CD4+CD25+ Treg cells, alleviating inflammatory responses. We have developed the recombinant fusion construct of mouse IL-35 (mIL-35)-hIgG1 Fc (hFc), in which EBI3 and IL-12p35 are joined by a flexible linker of (Gly4Ser)3. The mIg k-chain leader sequence at the amino terminus also allows secretion of the fusion protein. The mIL-35 construct was stably expressed in HEK 293 cells, and culture supernatants of single clones were screened by ELISA using a combination of anti-hFc and anti-mEBI3 antibodies, among which the most positive clone 35-5 was selected and adapted in a serum-free culture system. Functional activity of the secreted mIL-35 from this clone was tested using the [3H]thymidine-based cell proliferation assay. When CD4+ T cells purified from TCR-transgenic DO11.10 mice were stimulated with a combination of syngeneic irradiated APCs and OVA peptide in the presence of the mIL-35 culture supernatants, the mIL-35 significantly suppressed CD4+ T cell proliferation. Furthermore, the mIL-35-mediated inhibition of CD4+ T cell proliferation was reversed by anti-mIL-35 antibody. Taken together, these results demonstrate that the recombinant mIL-35 is functionally active and can be a useful research tool to study T cell-based immune regulations.

Dendritic Cell subsets: Functional analysis and TLR Phenotyping (98.13)

In-depth analysis of subtypes of Dendritic Cells (DCs), both myeloid (mDC) and plasmacytoid (pDC) subsets, has been developed through Toll-like Receptor (TLR) Phenotyping by Flow Cytometry. Sets of TLR specific mAbs are combined with cell lineage and DC markers like CD11c and CD123 for mDC and pDC, in a simple assay for consistent DC analysis. DC subsets in peripheral blood differ in origin, phenotype, and function as analyzed by cytokines, chemokines or pro-inflammatory factors produced upon interaction with pathogens. DC response to invading pathogens depends upon expression of a spectrum of receptors, such as TLRs, which are expressed on the cell surface and in intracellular endosomes. TLR signaling in DC subtypes results in production of cytokines, chemokines and pro-inflammatory factors that elicit and control adaptive immune responses. TLR Phenotyping analysis includes development of 4 color Flow Cytometry assay cocktails for TLR expression of DCs to characterize mDC or pDC in human peripheral blood. In combination with activation and functional markers such as cytokines or chemokines the assay system provides a new research tool to identify changes in TLR expression in steady state or pathogen infected conditions and during differentiation of monocytes, DCs, B cells/B cell lines (EBV transformation), or T cells. The approach also provides additional information on TLR signaling and downstream pro-inflammatory mediator production.

Endosomal damage and TLR2 mediated inflammasome activation by alkane particles in the generation of aseptic osteolysis

Ultra-high molecular weight polyethylene is widely used as a bearing surface in prosthetic arthroplasty. Over time the generation of implant-derived wear particles can initiate an inflammatory reaction characterized by periprosthetic inflammation and ultimately bone resorption at the prosthetic bone interface. Herein we present evidence that the different sized particles as well as the different length alkane polymers generated by implant wear leads to a two component inflammatory response. Polymeric alkane structures, with side chain oxidations, directly bind and activate the TLR-1/2 signaling pathway. Whereas micron- and nanometer-sized particulate debris are extensively phagocyted and induce enlargement, fusion and disruption of endosomal compartments. The resulting lysosomal damage and subsequent enzymatic leakage induces the NALP3 inflammasome activation as determined by cathepsins S and B cytosolic release, Caspase 1 activation and processing of pro-IL-1beta, and pro-IL-18. These two processes synergistically results in the initiation of a strong inflammatory response with consequent cellular necrosis and extracellular matrix degradation.

GMCSF in the absence of other cytokines sustains human dendritic cell precursors with T cell regulatory activity and capacity to differentiate into functional dendritic cells

Dendritic cell precursors, from human peripheral blood, express epitopes reactive with monoclonal antibodies specific for the empty conformation of HLA-DR1. Expression is substantially up-regulated during GMCSF-induced differentiation to immature dendritic cells, but is strongly down-regulated by IL-4. In the conventional protocol for in vitro generation of human dendritic cells from monocyte precursors, both GMCSF and IL-4 are used together, with IL-4 thought to have an effect on preventing macrophage outgrowth but not substantially altering the dendritic cell maturation pathway, whereas conventional protocols for generation of murine dendritic cells use GMCSF alone. We characterized human monocytes cultured in the presence of GMCSF and in the absence of IL-4, and found that the resultant cultures are stable for long periods in vitro, and have T cell stimulatory and immunodulatory activity characteristic of immature dendritic cells. Their response to maturation stimuli is weak in the absence of IL-4 but these cells retain the ability to differentiate into fully functional mature dendritic cells upon IL-4 treatment. We suggest that these cells may provide a useful model to investigate tolerogenic function as a developmental feature of DC and to understand molecular events involved in IL-4 priming for maturation.

Fluorogenic probes for monitoring peptide binding to class II MHC proteins in living cells

A crucial step in the immune response is the binding of antigenic peptides to major histocompatibility complex (MHC) proteins. Class II MHC proteins present their bound peptides to CD4(+) T cells, thereby helping to activate both the humoral and the cellular arms of the adaptive immune response. Peptide loading onto class II MHC proteins is regulated temporally, spatially and developmentally in antigen-presenting cells. To help visualize these processes, we have developed a series of novel fluorogenic probes that incorporate the environment-sensitive amino acid analogs 6-N,N-dimethylamino-2-3-naphthalimidoalanine and 4-N,N-dimethylaminophthalimidoalanine. Upon binding to class II MHC proteins these fluorophores show large changes in emission spectra, quantum yield and fluorescence lifetime. Peptides incorporating these fluorophores bind specifically to class II MHC proteins on antigen-presenting cells and can be used to follow peptide binding in vivo. Using these probes we have tracked a developmentally regulated cell-surface peptide-binding activity in primary human monocyte-derived dendritic cells.

Conformational Variation of Surface Class II MHC Proteins during Myeloid Dendritic Cell Differentiation Accompanies Structural Changes in Lysosomal MIIC

Dendritic cells (DC), uniquely among APC, express an open/empty conformation of MHC class II (MHC-II) proteins (correctly folded molecules lacking bound peptides). Generation and trafficking of empty HLA-DR during DC differentiation are investigated here. HLA-DR did not fold as an empty molecule in the endoplasmic reticulum/trans-Golgi network, did not derived from MHC/Ii complexes trafficking to the cell surface, but was generated after invariant chain degradation within lysosomal-like MHC-II rich compartments (MIIC). In pre-DC, generated from monocytes cultured in the presence of GM-CSF, Lamp-1(+)MHC-II(+) compartments are predominantly electron dense and, in these cells, empty MHC-II molecules accounts for as much as 20% of total surface HLA-DR. In immature DC, generated in presence of GM-CSF and IL-4, empty HLA-DR reside in multilamellar MIIC, but are scarcely observed at the cell surface. Thus, the morphology/composition of lysosomal MIIC at different DC maturational stages appear important for surface egression or intracellular retention of empty HLA-DR. Ag loading can be achieved for the fraction of empty HLA-DR present in the "peptide-receptive" form. Finally, in vivo, APC-expressing surface empty HLA-DR were found in T cell areas of secondary lymphoid organs.

Monoclonal Antibodies Specific for the Empty Conformation of HLA-DR1 Reveal Aspects of the Conformational Change Associated with Peptide Binding

Class II major histocompatibility complex (MHC) proteins bind peptides and present them at the cell surface for interaction with CD4+ T cells as part of the system by which the immune system surveys the body for signs of infection. Peptide binding is known to induce conformational changes in class II MHC proteins on the basis of a variety of hydrodynamic and spectroscopic approaches, but the changes have not been clearly localized within the overall class II MHC structure. To map the peptide-induced conformational change for HLA-DR1, a common human class II MHC variant, we generated a series of monoclonal antibodies recognizing the beta subunit that are specific for the empty conformation. Each antibody reacted with the empty but not the peptide-loaded form, for both soluble recombinant protein and native protein expressed at the cell surface. Antibody binding epitopes were characterized using overlapping peptides and alanine scanning substitutions and were localized to two distinct regions of the protein. The pattern of key residues within the epitopes suggested that the two epitope regions undergo substantial conformational alteration during peptide binding. These results illuminate aspects of the structure of the empty forms and the nature of the peptide-induced conformational change.

Protection against chronic infection and AIDS by an HIV envelope peptide-cocktail vaccine in a pathogenic SHIV-rhesus model

Based on our prior studies in mouse, monkey, chimpanzee, and human experimental systems, we identified six peptides encoded by highly conserved regions of the human immunodeficiency virus type 1 (HIV-1) envelope gene that selectively induce cellular immune responses in the absence of anti-viral antibody production. We tested a cocktail of the six peptides as a prototype vaccine for protection from simian human immunodeficiency virus (SHIV) infection and acquired immunodeficiency syndrome (AIDS) in a rhesus monkey model. Three monkeys were vaccinated with the peptide cocktail in Freund's adjuvant followed by autologous dendritic cells (DC) pulsed with these peptides. All the vaccinated animals exhibited significant induction of T-cell proliferation and cytotoxic T lymphocytes (CTL) responses, but no neutralizing antibodies. Two control mock-vaccinated monkeys showed no specific immune responses. Upon challenge with the pathogenic SHIV(KU-2), both the control and vaccinated monkeys were infected, but efficient clearance of virus-infected cells was observed in all the three vaccinated animals within 14 weeks. These animals also experienced a boosting of antiviral cellular immune responses after infection, and maintained antigen-specific IFN-gamma-producing cells in circulation beyond 42 weeks post-challenge. In contrast, the two mock-vaccinated monkeys had low to undetectable cellular immune responses and maintained significant levels of viral-infected cells and infectious virus in circulation. Further, in both the control monkeys plasma viremia was detectable beyond 38 weeks post-challenge indicating chronic phase infection. In one control monkey, the CD4+ cells dropped to very low levels by 2 weeks post-challenge and became undetectable by week 39 coinciding with high plasma viremia and AIDS, which included cachexia and ataxia. These results serve as proof of principle for the effectiveness of the HIV envelope peptide cocktail vaccine against chronic infection and AIDS, and support the development of multivalent peptide-based vaccine as a viable strategy to induce cell-mediated immunity (CMI) for protection against HIV and AIDS in humans.