Illuminating T cell-dendritic cell interactions in vivo by FlAsHing antigens

Delineating the complex network of interactions between antigen-specific T cells and antigen presenting cells (APCs) is crucial for effective precision therapies against cancer, chronic infections, and autoimmunity. However, the existing arsenal for examining antigen-specific T cell interactions is restricted to a select few antigen-T cell receptor pairs, with limited in situ utility. This lack of versatility is largely due to the disruptive effects of reagents on the immune synapse, which hinder real-time monitoring of antigen-specific interactions. To address this limitation, we have developed a novel and versatile immune monitoring strategy by adding a short cysteine-rich tag to antigenic peptides that emits fluorescence upon binding to thiol-reactive biarsenical hairpin compounds. Our findings demonstrate the specificity and durability of the novel antigen-targeting probes during dynamic immune monitoring in vitro and in vivo. This strategy opens new avenues for biological validation of T-cell receptors with newly identified epitopes by revealing the behavior of previously unrecognized antigen-receptor pairs, expanding our understanding of T cell responses.

Illuminating T cell-dendritic cell interactions in vivo by FlAsHing antigens

Delineating the complex network of interactions between antigen-specific T cells and antigen presenting cells (APCs) is crucial for effective precision therapies against cancer, chronic infections, and autoimmunity. However, the existing arsenal for examining antigen-specific T cell interactions is restricted to a select few antigen-T cell receptor pairs, with limited in situ utility. This lack of versatility is largely due to the disruptive effects of reagents on the immune synapse, which hinder real-time monitoring of antigen-specific interactions. To address this limitation, we have developed a novel and versatile immune monitoring strategy by adding a short cysteine-rich tag to antigenic peptides that emits fluorescence upon binding to thiol-reactive biarsenical hairpin compounds. Our findings demonstrate the specificity and durability of the novel antigen-targeting probes during dynamic immune monitoring in vitro and in vivo. This strategy opens new avenues for biological validation of T-cell receptors with newly identified epitopes by revealing the behavior of previously unrecognized antigen-receptor pairs, expanding our understanding of T cell responses.

Illuminating T cell-dendritic cell interactions in vivo by FlAsHing antigens

Delineating the complex network of interactions between antigen-specific T cells and antigen presenting cells (APCs) is crucial for effective precision therapies against cancer, chronic infections, and autoimmunity. However, the existing arsenal for examining antigen-specific T cell interactions is restricted to a select few antigen-T cell receptor pairs, with limited in situ utility. This lack of versatility is largely due to the disruptive effects of reagents on the immune synapse, which hinder real-time monitoring of antigen-specific interactions. To address this limitation, we have developed a novel and versatile immune monitoring strategy by adding a short cysteine-rich tag to antigenic peptides that emits fluorescence upon binding to thiol-reactive biarsenical hairpin compounds. Our findings demonstrate the specificity and durability of the novel antigen-targeting probes during dynamic immune monitoring in vitro and in vivo. This strategy opens new avenues for biological validation of T-cell receptors with newly identified epitopes by revealing the behavior of previously unrecognized antigen-receptor pairs, expanding our understanding of T cell responses.

Cerebral Malaria Is Regulated by Host-Mediated Changes in Plasmodium Gene Expression

Cerebral malaria (CM), the deadliest complication of Plasmodium infection, is a complex and unpredictable disease. However, our understanding of the host and parasite factors that cause CM is limited. Using a mouse model of CM, experimental CM (ECM), we performed a three-way comparison between ECM-susceptible C57BL/6 mice infected with ECM-causing Plasmodium ANKA parasites [ANKA(C57BL/6)], ECM-resistant BALB/c mice infected with Plasmodium ANKA [ANKA(BALB/c)], and C57BL/6 mice infected with Plasmodium NK65 that does not cause ECM [NK65(C57BL/6)]. All ANKA(C57BL/6) mice developed CM. In contrast, in ANKA(BALB/c) and NK65(C57BL/6), infections do not result in CM and proceed similarly in terms of parasite growth, disease course, and host immune response. However, parasite gene expression in ANKA(BALB/c) was remarkably different than that in ANKA(C57BL/6) but similar to the gene expression in NK65(C57BL/6). Thus, Plasmodium ANKA has an ECM-specific gene expression profile that is activated only in susceptible hosts, providing evidence that the host has a critical influence on the outcome of infection. IMPORTANCE Hundreds of thousands of lives are lost each year due to the brain damage caused by malaria disease. The overwhelming majority of these deaths occur in young children living in sub-Saharan Africa. Thus far, there are no vaccines against this deadly disease, and we still do not know why fatal brain damage occurs in some children while others have milder, self-limiting disease progression. Our research provides an important clue to this problem. Here, we showed that the genetic background of the host has an important role in determining the course and the outcome of the disease. Our research also identified parasite molecules that can potentially be targeted in vaccination and therapy approaches.

Contributions of Diet and Age to Ulcerative Dermatitis in Female C57BL/6J Mice

C57BL/6J (B6) mice are commonly affected by ulcerative dermatitis (UD), a disease of unknown etiology with poor response to treatment. To study the possible role of diet in UD, we compared skin changes in B6 female mice fed a high-fat diet with those of mice fed a control diet. In addition, skin samples from mice with no, mild, moderate, and severe clinical signs of UD were examined by light and transmission electron microscopy (TEM). Mice fed a high-fat diet for 2 mo had more skin mast cell degranulation than did mice fed the control diet for the same period. Regardless of diet, older mice had more skin mast cells and more of these cells were degranulating as compared with younger mice. Microscopic changes in very early lesions were characterized by an increase in dermal mast cells and degranulation with focal areas of epidermal hyperplasia with or without hyperkeratosis. As the condition progressed, a mixed but predominantly neutrophilic inflammatory cell infiltrate appeared in the dermis, with or without epidermal erosion and scab formation. TEM showed that dermal mast cell membranes had disrupted and released of large number of electron dense granules, whereas degranulated mast cells were filled with isolated and coalescing empty spaces due to fusion of granule membranes. Ulceration appeared to occur very quickly, probably as result of intense scratching due to the pruritogenic properties of the histamine released from mast cell granules. This study showed a direct correlation between dietary fat and skin mast cell degranulation in female B6 mice. In addition, the number of skin mast cells and degranulation rates was higher in older mice. Treatments directed at preventing mast cell degranulation may result in better outcomes when applied early in UD cases. As noted previously in studies using caloric restriction, lower fat content in rodent diets may help prevent UD.

Modified cued recall test in the French population with Down syndrome: A retrospective medical records analysis

BACKGROUND

Adults with Down syndrome (DS) are at increased risk of developing Alzheimer's disease (AD) due to genetic predisposition. Identification of patients with AD is difficult since intellectual disabilities (ID) may confound diagnosis. The objective of this study was to evaluate the ability of the French version of the modified cued recall test (mCRT) to distinguish between subjects with and without AD in the adult DS population.

METHODS

This was a retrospective, single-centre, medical records study including data between March 2014 and July 2020. Adults aged ≥30 years with DS who had at least one mCRT record available were eligible. Age, sex and ID level were extracted, and subjects were attributed to three groups: patients with AD, patients with co-occurring conditions that may impact cognitive function and subjects without AD. mCRT scores, adjusted by sex, age and ID level, were compared between groups. The optimal cut-off value to distinguish between patients with and without AD was determined using the receiver operating characteristic curve. The impact of age and ID level on mCRT scores was assessed.

RESULTS

Overall, 194 patients with DS were included: 12 patients with AD, 94 patients with co-occurring conditions and 88 healthy subjects. Total recall scores were significantly lower (P < 0.0001) in patients with AD compared with healthy subjects. The optimal cut-off value to discriminate between patients with AD and healthy subjects was 22, which compares well with the cut-off value of 23 originally reported for the English version of the mCRT. Patients aged 30-44 years had higher mCRT total recall scores compared with patients aged ≥45 years (P = 0.0221). Similarly, patients with mild ID had higher mCRT scores compared with patients with severe ID (P < 0.0001).

INTERPRETATION

The mCRT is a sensitive tool that may help in the clinical diagnosis of AD in subjects with DS. Early recognition of AD is paramount to deliver appropriate interventions to this vulnerable population.

Analysis of Mitochondrial Performance in Lymphocytes Using Fluorescent Lifetime Imaging Microscopy

During lymphocyte maturation and differentiation, cells undergo a series of proliferative stages interrupted with stages of low activity. The rapid proliferation stages are marked by changes in metabolic outputs-adapting to energy demands by either hindering or utilizing metabolic pathways. As such, it is necessary to view these changes in real time; however, current strategies for metabolomics are time consuming and very rarely provide a holistic profile of the cellular metabolism while also characterizing mitochondrial metabolism. Here, we devised a fluorescence lifetime imaging microscopy (FLIM) strategy to image mitochondrial metabolic profiles in lymphocytes as they go through changes in metabolic activity. Our method provides not only a comprehensive view of cellular metabolism but also narrow in mitochondrial contributions while also efficiently excluding non-viable cells with and without the use of a viability dye. Our novel imaging strategy offers a reliable tool to study changes in mitochondrial metabolism.

Metacarpal squeezing reduces grip strength

Unduly tight plaster hand casts may narrow the metacarpal joint space, hindering rehabilitation. This study investigated how metacarpal narrowing affects grip strength. Forty-two adult volunteers with no other pathology were included. Dominant and non-dominant hand grip strength was measured with a digital hand dynamometer (Jamar plus, China). Metacarpal width was measured with a metal caliper, and the caliper was then fixed at 10% narrowing of the joint space, and a second measurement of grip strength was taken. The measurements were thus taken twice each in the dominant and non-dominant hand, and the average of the two was recorded. A total 336 measurements were taken in the dominant and non-dominant hands of 42 individuals at two time points. There was no significant difference in grip strength between dominant and non-dominant hands (p = 0.183). After 10% narrowing, both the dominant and the non-dominant hand showed a mean 33.4% reduction in grip strength: i.e., squeezing the metacarpus with a caliper significantly reduced grip strength in both dominant and non-dominant hands (p = 0.01). The study thus showed that grip strength will decrease significantly when the metacarpus is squeezed by a tight cast. Although the patient does not feel the 10% narrowing of the metacarpus, it is clear that hand muscle mass may be adversely affected in the long term.

Muscle strength but not balance improves after arthroscopic biodegradable polyurethane meniscus scaffold application

PURPOSE

This study aimed to assess the impact of biodegradable polyurethane meniscus scaffold implantation (BPMSI) on muscle strength and balance in comparison with the healthy contralateral knee in patients with irreparable medial meniscus defect.

METHODS

This observational and prospective case-cohort study was conducted with patients who had irreparable meniscal defects and underwent arthroscopic meniscus scaffold implantation. Surgeries were carried out on the medial meniscus of 16 right and 4 left knees. Visual analog scale (VAS) was used to assess the degree of pain relief. Knee Injury and Osteoarthritis Outcome Score (KOOS) and Lysholm (LYS) score were used to evaluate the functional improvement at weeks 12, 24 and 36. Concentric and eccentric quadriceps and hamstring peak torque (PT) as well as the peak torque-to-body weight (PTB) ratio, anterior-posterior, mediolateral and overall stability indexes were assessed at the same time points.

RESULTS

Twenty male patients with a mean age and body mass index of 32.2 ± 8.8 years and 26.2 ± 4.2 kg/m², respectively, were included in the study. The amount of pain decreased from 7.6 ± 1.5% to 2.9 ± 1.5% at postoperative week 36. Range of motion, Lysholm score and KOOS increased from 87.0^ο ± 9.5^ο to 115.0^ο ± 15.1^ο, 30.8 ± 4.3 to 81.5 ± 5.3 and 37.4 ± 5.3 to 74.1 ± 7.2, respectively. Concentric quadriceps and hamstring peak torque values and peak torque/body weight ratios were improved in the knees that received a meniscus scaffold implant. Anterior/posterior, medial/lateral, and overall stability indexes with or without biofeedback exhibited a slight improvement, which was not statistically significant.

CONCLUSION

BPMSI led to decreased pain and improved function at postoperative week 36. Although muscle strength almost returned to normal, balance parameters did not recover within 36 weeks after the procedure.

Testing the impact of a single nucleotide polymorphism in a Plasmodium berghei ApiAP2 transcription factor on experimental cerebral malaria in mice

Cerebral malaria (CM) is the deadliest form of severe Plasmodium infections. Currently, we have limited understanding of the mechanisms by which Plasmodium parasites induce CM. The mouse model of CM, experimental CM (ECM), induced by infection with the rodent parasite, Plasmodium berghei ANKA (PbANKA) has been extensively used to study the pathophysiology of CM. Recent genomic analyses revealed that the coding regions of PbANKA and the closely related Plasmodium berghei NK65 (PbNK65), that does not cause ECM, differ in only 21 single nucleotide polymorphysims (SNPs). Thus, the SNP-containing genes might contribute to the pathogenesis of ECM. Although the majority of these SNPs are located in genes of unknown function, one SNP is located in the DNA binding site of a member of the Plasmodium ApiAP2 transcription factor family, that we recently showed functions as a virulence factor alternating the host’s immune response to the parasite. Here, we investigated the impact of this SNP on the development of ECM. Our results using CRISPR-Cas9 engineered parasites indicate that despite its immune modulatory function, the SNP is neither necessary nor sufficient to induce ECM and thus cannot account for parasite strain-specific differences in ECM phenotypes.

A single-nucleotide polymorphism in a Plasmodium berghei ApiAP2 transcription factor alters the development of host immunity

The acquisition of malaria immunity is both remarkably slow and unpredictable. At present, we know little about the malaria parasite genes that influence the host's ability to mount a protective immune response. Here, we show that a single-nucleotide polymorphism (SNP) resulting in a single amino acid change (S to F) in an ApiAP2 transcription factor in the rodent malaria parasite Plasmodium berghei (Pb) NK65 allowed infected mice to mount a T helper cell 1 (T_H1)-type immune response that controlled subsequent infections. As compared to PbNK65^S, PbNK65^F parasites differentially expressed 46 genes, most of which are predicted to play roles in immune evasion. PbNK65^F infections resulted in an early interferon-γ response and a later expansion of germinal centers, resulting in high levels of infected red blood cell-specific T_H1-type immunoglobulin G2b (IgG2b) and IgG2c antibodies. Thus, the Pb ApiAP2 transcription factor functions as a critical parasite virulence factor in malaria infections.

B cell signaling in context

Over the past several decades, B cell antigen receptor (BCR)-induced signaling pathways have been described in extraordinary molecular detail, mainly from studies of B cell responses to antigens in vitro. BCR signaling has been shown to govern the initiation of transcriptional programs associated with B cell activation and fate decisions, as well as the BCR-dependent processing of antigen and presentation of antigen to T cells. However, although the potential of the BCR to orchestrate B cell behavior was known, there was no clear appreciation of the context in which B cells signal in secondary lymphoid organs in vivo or how that context influences signaling. In this Review, we describe the current view of the cellular consequences of BCR signaling and advances in the understanding of B cell signaling in context in vivo.

Tbet provides survival advantage to Tregs during Type 1 inflammation

Regulatory T-cells (Tregs) comprise subgroups with transcriptional programs similar to helper T-cell lineages. To visualize Tbet expression by Tregs during a T helper 1 (Th1) driven inflammation induced by Complete Freund’s Adjuvant in vivo, we imaged Tregs in the lymph nodes of a Tbet.ZsGreen-Foxp3.RFP mouse. While the majority of conventional Foxp3+ Tregs, resided within the T-cell zone, Tbet+Foxp3+ Tregs localized to the interfollicular zone that also contained the recently activated Th1 cells. To understand whether Tbet serves merely as a marker of activation or plays an actual role in Treg function, we generated bone marrow chimeras from Tbet+/+ and Tbet−/− mice. The peripheral Treg pool in chimeric mice was equally constituted by the Tbet+/+ and Tbet−/− cells. However, when the mice were challenged with Plasmodium chabaudi, a parasite that initiates a strong systemic Th1 response, the Treg compartment was significantly dominated by Tbet+/+ Tregs that displayed increased Tbet expression over time. While Tbet+/+ and Tbet−/− Tregs displayed similar activation status and proliferation, Tbet−/− Treg were more prone to apoptosis. Furthermore, Tbet−/− Tregs expressed lower levels of the ATP ectonucleotidase CD39 that was more pronounced during the peak of infection. Pharmacological inhibition of the activity of CD39 increased apoptosis of Tbet+/+ but not Tbet−/− Tregs in an ATP enriched culture in-vitro, suggesting a positive correlation between the availability of Tbet, CD39 activity and viability. Taken together, Tbet may preserve the ability of Tregs to cope with elevated toxic extracellular ATP at the inflammation site by tuning their CD39 expression or activity.

Prolonged activation in CD4+ T cells results in extensive mitochondrial remodeling despite the metabolic dominance of aerobic glycolysis

Activation of CD4+ T cells to proliferate drives cells toward aerobic glycolysis for energy production while using mitochondria primarily for macromolecular synthesis. In addition, the mitochondria of activated T cells increase production of reactive oxygen species, providing an important second messenger for intracellular signaling pathways. To better understand the critical changes in mitochondria that accompany prolonged T cell activation, we carried out an extensive analysis of mitochondrial remodeling using a combination of conventional strategies and a novel high-resolution imaging method. We show that for four days following activation, mouse CD4+ T cells sustained their commitment to glycolysis facilitated by increased glucose uptake through increased expression of GLUT transporters. Despite their limited contribution to energy production, mitochondria were active and showed increased reactive oxygen species production. Despite elevated ROS production, it was successfully counterbalanced by antioxidant enzymes, hence the mitochondria did not display signs of oxidative stress as evidenced by the healthy cristae structure and overall morphology as well as the maintained mitochondrial reserve. Moreover, prolonged activation of CD4+ T cells led to increases in mitochondrial content and volume, in the number of mitochondria per cell and in mitochondrial biogenesis. Thus, during prolonged activation, CD4+ T cells continue to obtain energy predominantly from glycolysis but also undergo extensive mitochondrial remodeling, resulting in increased mitochondrial activity.

Regulatory T cells perform antigen specific suppression by depleting cognate peptide-MHC class II via trogocytosis

Tregs are professional suppressors of the immune response, yet their mechanism of action in vivo remains unclear. Using electron microscopy and dynamic intravital two-photon microscopy, we revealed that unlike effector T cells, Tregs displayed a distinct morphology with membrane projections that resemble filopodia at the DC binding site increasing the surface area of the contact dramatically. Despite the intense contact with DC, Tregs only abolished the interactions of effector T cells with DC when the effectors shared the same antigen specificity with Tregs. However, this cessation of the effector T cell interactions was not due to a physical hindrance created by the superior binding ability of Treg since the antigen specific inhibition of T cell-DC interaction was still observed after Tregs are removed from the environment. Instead, the antigen-specific inhibition was secondary to the removal of cognate peptide-MHC Class II (pMHCII) from the surface of DC as evidenced by the strictly antigen-specific depletion of the pMHCII from double antigen pulsed DC. pMHCII capture was only performed by antigen specific Treg, not by polyclonal Treg and it was not secondary to the interaction of CTLA-4 with B7 molecules suggesting the functional importance of TCR in Treg suppression. Prominent members of the B7 family, that are not de novo expressed in Tregs, such as CD86, ICOSL and PD-L2 were acquired alongside the TCR, suggestive of a process that includes a membrane transfer event called trogocytosis. Altogether, we propose antigen specific depletion of peptide-MHCII complexes via trogocytosis as a new mechanism for Treg-mediated suppression.

Use of modified peptides for live tracking of peptide-MHCII complexes during antigenspecific T cell-dendritic cell interactions

The recognition of peptide-MHC class II complexes (pMHCII) presented by dendritic cells (DCs) is critical for the activation of CD4+ T cells, and proper detection of such complexes is essential for understanding T cell-DC interactions. However, current detection methods for pMHCII complexes using antibodies may block cellular interactions, limiting their use, while conventional tags, such as GFP, are too large to be loaded onto MHCII without disrupting its function. To probe pMHCII complexes, we constructed a variant of the ovalbumin peptide (OVA323–339) linked to a tetracysteine tag (CCPGCC), which can be treated with organoarsenic compounds to induce fluorescence. This modified peptide retained its functionality as it was able to stimulate T cells to the same degree as the unmodified peptide. We also analyzed signal specificity both at the pMHCII level, by using MHCII−/− APCs, and at a broader level by quenching endogenous tetracysteine expression, and confirmed that our fluorescent signal was derived from the peptide modification. We then used microscopy to visualize pMHCII movement after interaction of pulsed DCs with OVA-specific T cells in vitro and subsequently in vivo, and detected a gradual increase of pMHCII complexes at the synapse. Interestingly, we also observed a transfer of fluorescent signal from DCs to antigen-specific T cells, but not to polyclonal T cells, indicating acquisition of pMHCII, which we were able to quantify. Taken together, our results show a non-disruptive approach to assay pMHCII, and provide a window to observe intricate T cell-DC interactions in real-time.

Characterization of a novel Plasmodium Virulence Factor

Plasmodium is a deadly parasite that claims lives of nearly half a million individuals each year. Identification of the mechanisms the parasite uses to evade the immune response is a critical goal to develop the much needed vaccine against this pathogen. However, we know very little about how individual parasite genes function. Here, by using CRISPR/Cas9 strategy, we altered the DNA binding domain of a Transcription Factor (TF) (PBANKA_011210) that is essential for the completion of Plasmodium Berghei life cycle. In mice, compared to the WT parasite, the mutant one showed differential expression of 46 genes, most of which are thought to be involved in generating parasite surface antigen diversity. Furthermore, unlike WT parasite which successfully hides from immune system, mutant parasite triggered high levels of IFN-g which translated into formation of prolonged germinal centers and development of higher titers of parasite specific IgG2b and IgG2c type antibodies. At low inoculum levels this resulted in successful clearance of infection and development of protective immunological memory in mutant parasite infected animals in contrast to a deadly outcome in WT parasite infected group. The differential development of the immune response was dependent on the host’s ability to produce IFNg as the phenotype was lost in IFNg KO mice. We therefore conclude that (PBANKA_011210) TF is a novel virulence factor acts as an immune modulator and dampens IFNg mediated immune response against parasite

How TLR9 Signaling shapes the survival, differentiation and the metabolism of B cells

The signaling cascades initiated by binding of the antigen to B cell receptor (BCR) leads to rapid increases in cellular respiration, nutrient uptake and expression of various activation markers. However, unless a second, independent stimulus is received soon after antigen binding, BCR signaling does not lead to B cell proliferation and differentiation. Instead, BCR signaling alone leads to a dysregulation of cellular calcium homeostasis which in turn causes mitochondrial dysfunction and a phenomenon called activation induced cell death. The second signal can be provided by Toll like receptor (TLR) signaling, indicating the presence of an acute infection or through B cell-T cell interactions that rules out that the initial antigen was a prohibited self-antigen. Additionally, there is an interplay between TLR versus T cell mediated second signals, namely that TLR signaling trumped the need for the antigen-stimulated B cell to interact with T cells to receive a ‘go’ signal. TLR stimulation decreased B cells’ ability to capture, process and present antigens to solicit help from T cells. Rather TLRs directly boosted B cell antibody and cytokine secretion and proliferation. Thus, TLR signals drive B cells toward rapid T cell-independent differentiation to plasma cells providing rapid neutralizing antibody production to fight off infections quickly. In contrast B cells that receive their survival signals from T cells are induced to undergo a time-consuming process that is necessary for antibody affinity maturation and long-lasting immune memory. Therefore, the TLR driven shortcut to quick antibody comes with a price which is the absence of “crème de la crème” antibodies that would protect the body from subsequent infections for years to come.

Regulatory T cells mediate specific suppression by depleting peptide-MHC class II from dendritic cells

T regulatory cells (T_regs) can activate multiple suppressive mechanisms in vitro upon activation via the T cell receptor resulting in antigen-independent suppression. However, it remains unclear whether similar pathways operate in vivo. Here, we found that antigen-specific T_regs activated by dendritic cells (DCs) pulsed with two antigens suppressed T_naive specific for both cognate and non-cognate antigens in vitro, but only suppressed T_naive specific for cognate antigen in vivo. Antigen-specific T_regs formed strong interactions with DC resulting in selective inhibition of the binding of T_naive to cognate antigen, yet allowing bystander T_naive access. Strong binding resulted in removal of the cognate peptide-MHCII (pMHCII) from the DC surface reducing the capacity of the DC to present antigen. The enhanced binding of T_regs to DC coupled with their capacity to deplete pMHCII represents a novel pathway for T_reg-mediated suppression and may be a mechanism by which T_regs maintain immune homeostasis.

Increased Mitochondrial Biogenesis and Reactive Oxygen Species Production Accompany Prolonged CD4+ T Cell Activation

Activation of CD4⁺ T cells to proliferate drives cells toward aerobic glycolysis for energy production while using mitochondria primarily for macromolecular synthesis. In addition, the mitochondria of activated T cells increase production of reactive oxygen species, providing an important second messenger for intracellular signaling pathways. To better understand the critical changes in mitochondria that accompany prolonged T cell activation, we carried out an extensive analysis of mitochondrial remodeling using a combination of conventional strategies and a novel high-resolution imaging method. We show that for 4 d following activation, mouse CD4⁺ T cells sustained their commitment to glycolysis facilitated by increased glucose uptake through increased expression of GLUT transporters. Despite their limited contribution to energy production, mitochondria were active and showed increased reactive oxygen species production. Moreover, prolonged activation of CD4⁺ T cells led to increases in mitochondrial content and volume, in the number of mitochondria per cell and in mitochondrial biogenesis. Thus, during prolonged activation, CD4⁺ T cells continue to obtain energy predominantly from glycolysis but also undergo extensive mitochondrial remodeling, resulting in increased mitochondrial activity.

Second signals rescue B cells from activation-induced mitochondrial dysfunction and death

B cells are activated by two temporally distinct signals, the first provided by antigen binding to the B cell antigen receptor (BCR) and the second by T helper cells. Here we show that B cells responded to antigen by rapidly increasing metabolic activity including both oxidative phosphorylation and glycolysis. In the absence of a second signal B cells progressively lost mitochondrial function and glycolytic capacity leading to apoptosis. Mitochondrial dysfunction was a result of the gradual accumulation of intracellular calcium through calcium response activated calcium channels that was preventable for approximately nine hours after B cell antigen binding by either T helper cells or Toll-like receptor 9 signaling. Thus, BCR signaling appears to activate a metabolic program that imposes a limited time window in which B cells either receive a second signal and survive or are eliminated.

A novel multicolor stimulated emission depletion (STED) microscopy strategy to visualize mitochondrial morphology in lymphocytes

Immunometabolism is an emerging field that studies the activation-induced reprogramming required to alter immune cell function and meet new energetic demands. In-depth investigations of the metabolism-related cellular changes necessitate high-resolution visualization of mitochondria. However, current strategies for imaging mitochondria are optimized for model cells with high cytoplasm-to-nucleus ratios and are not readily adaptable for many immune cells. Here, we devised a multicolor STED microscopy method to assess B lymphocyte mitochondria in resting and activated states. By staining specimens with TOM-20 and MitoTracker dyes, as well as DAPI and a viability dye, our strategy allowed us to assess the morphology and volumes of mitochondria while efficiently excluding dead cells. Our analyses showed that stimulation of B lymphocytes via toll-like receptor 9 (TLR9) and/or B cell receptor (BCR) led to notable mass and volume increases in individual mitochondria within 24 hours. Furthermore, TLR9-stimulated cells demonstrated more tubular and connected mitochondrial networks consistent with their higher metabolic demands. In addition, collecting images of the same specimens side-by-side on AiryScan and standard confocal laser microscopes showed that STED microscopy performed significantly better in resolving changes in 3D mitochondrial morphology. However, none of the light microscopy imaging strategies could resolve activation-induced structural alterations in cristae or mitochondrial matrix. In conclusion, our novel STED-based multicolor imaging approach offers a powerful super-resolution tool to study immunometabolism and mitochondrial reorganization in lymphocytes at the whole cell level.

The role of transcription factor T-bet in B cell mediated responses to Plasmodium infection

Malaria is a global health concern which affects over 200 million individuals worldwide. Although the immune system rapidly responds to Plasmodium infection with specific antibodies, natural antibodies fail to establish long term protection, often leading to repetitive infections and chronicity. Recent studies showed that in a chronic malaria setting both B cells and T cells induce expression of T-bet transcription factor. It is not completely understood whether this is a part of the specific host defense or a result of disease pathogenesis. Here using transgenic mouse models, we show that knockout of T-bet or IFN-g similarly reduces survival of mice compared to WT upon infection with Plasmodium chabaudi, therefore suggesting a protective role for T-bet. To determine the specific role T-bet plays in B cell responses to Plasmodium, we first identified that T-bet expression in mouse B cells are triggered by dual stimulation of IFN-g and B cell receptor. Similarly using Tbet-zsgreen transgenic mice we showed that conditions specific to Plasmodium chabaudi infection drive T-bet expression in multiple B cell subsets in a time dependent fashion. However, no such induction is shown when mice are immunized with T-dependent protein antigens adjuvanted with Alum. On the other hand, bone marrow chimeric animals reconstituted with equal amounts of congenically labeled WT and T-bet KO bone marrow cells showed that for most B cell subsets the lack of T-bet does not change the ratio of WT and KO cells upon Plasmodium infection indicating that T-bet expression may not be equally critical for all B cell responses to infection. These findings suggest a complex role of T-bet in the development of humoral responses.

Elucidating synergistic and antagonistic effects of B cell receptor and toll-like receptors 3, 4, and 9 in B cell activation

B cells are key components of the humoral immune response. Two forms of B cell activation come from engagement of the B cell receptor (BCR) with foreign antigens and from pathogen-associated molecular patters (PAMPs) binding to toll-like receptors (TLRs). For TLRs, MyD88 and TRIF are the major adaptors that lead to NFkB and IRF3 activation respectively. Among various TLRs that are present in B cells, TLR9 is only able to use MyD88 and TLR3 only signals through TRIF, while TLR4 uses both pathways. Therefore, these TLRs provide excellent tools to investigate the roles of TRIF and MyD88 pathways in B cell function and the interplay between them. Here, using stimulation through these three different TLRs either individually or in combination with each other and with/or without anti-IgM, we observed that there is synergy and antagonism between these pathways in terms of activation induced metabolic boost, cytokine production, IgM secretion, expression of various cell surface markers, and antigen presentation. We identified the TRIF pathway as an inducer of Type-I interferon secretion by B cells, which eventually favors the expression of costimulatory molecules such as CD86. On the other hand, MyD88 stimulation antagonized the expression of costimulatory molecules and dramatically induced rapid proliferation and production of IgM as well as proinflammatory cytokines such as IL-6 and TNF. Using B cells obtained from MyD88 or TRIF KO mice, we showed that the interplay between pathways is of limited scale; however, for TLR4 signaling MyD88 has a largely permissive effect while TRIF determines the magnitude of response. These results further our understanding of the complex TLR signaling machinery in B lymphocytes.

Antigen binding to B cells activates a metabolic program that in the absence of a second signal leads to mitochondrial dysfunction and cell death

Activation of B cells to proliferate and differentiate into antibody secreting cells is regulated to avoid unwanted antibody responses by two temporally distinct signals, the first provided by antigen binding to the B cell receptor (BCR) and the second by T helper cells. Despite the central role of these two signals in driving antibody responses, our understanding of the consequences of each signal is incomplete. Here using in vitro and in vivo models, we investigated the metabolic changes that accompany B cell activation and show that antigen binding to the BCR signals for rapid increases in both oxidative phosphorylation and glycolysis, however early events following antigen engagement including spreading and contraction of antigen bound BCR and internalization of the bound antigen depend solely on the energy produced by oxidative phosphorylation. Changes in gene expression, mitochondrial performance and glucose uptake follow the initial activation, preparing the cells to respond to a second signal. However, in the absence of a second signal B cells undergo progressive loss of mitochondria function and glycolytic capacity ultimately leading to apoptosis. Mitochondria dysfunction is a result of the gradual accumulation of intracellular calcium which leads to inefficient oxidative phosphorylation and increased ROS production and eventually swollen patches of mitochondria. This process can be avoided for approximately nine hours after B cell antigen binding by either T helper cells or by signaling through Toll-like receptor 9. Thus, antigen binding to B cells appears to activate a metabolic program that imposes a short time window in which B cells either receive a second signal and survive or alternatively face elimination.

Toll-like receptor 9 signaling antagonizes B cell antigen capture, processing and presentation resulting in a failure to activate helper T cells

Key events in T cell-dependent antibody responses, including the formation of germinal centers and affinity selection, are dependent on the ability of B cells to capture antigen and present it to follicular helper T cells. Despite its importance, little is known about the regulation of this critical B cell function. Here we show that although TLR9 signaling induced B cell proliferation, secretion of cytokines and IgM, it blocked the ability of antigen-specific B cells to capture, process and present antigen. In the presence of the TLR9 agonist, CpG, B cells were less able to form synapses with antigen-containing membranes and to pull antigen from them. CpG also diminished the ability of the BCR to deliver internalized antigen to antigen processing compartments resulting in fewer MHC-peptide complexes on the B cell surface. Additionally CpG blocked the BCR-induced increases in the expression of both MHC class II and important co-receptors, including CD86, resulting in the inability of B cells to activate antigen-specific CD4+ T cells. A principle component analysis of RNA seq data showed little overlap between B cells stimulated through the BCR or TLR9 alone or together indicating that TLR9 antagonism of BCR-dependent antigen presentation is through the activation of a novel transcriptional program. In a chimeric mouse model and in a human clinical trial the TLR9 agonist, CpG, enhanced the magnitude of the antibody response to a protein vaccine but failed to promote affinity maturation. Thus, TLR9 signaling may enhance the magnitude of an antibody response at the expense of the ability of B cells to engage in germinal center events that are highly dependent on antigen capture and presentation.

Tetracysteine tagged OVA (323–339) peptide as a novel tool for visualizing peptide-MHCII complexes in primary mouse cells

Professional APCs present peptides to CD4+ T cells in the context of MHCII. To understand the dynamics of peptide-MHCII complexes in T cell-APC interaction, real-time visualization of these complexes is crucial. However, current reagents such as peptide specific MHCII antibodies do not allow one to probe peptide-MHCII dynamics during live interactions in vivo, as they also block T cell-APC interactions. Fluorescent tags such as green fluorescent protein (GFP) consist of more than 200 amino acids and have the potential of disrupting the functionality of the antigenic peptides. Therefore, we constructed an OVA(323–339) peptide containing a pro-fluorescent tetracysteine tag (CCPGCC) at the C-terminus with aminocaproic acid linker (OVACACA). First, we tested whether the addition of tag had an impact on T cell stimulation and found that OVACACA pulsed APCs could activate OTII cells to same degree as OVA(323–339). Secondly, we treated the APCs with an organoarsenic compound to switch on the fluorescence and measured the signal by flow cytometry. We showed that the fluorescent signal specifically was derived from OVACACA-MHCII, as neither MHCII−/− APCs pulsed with OVACACA, nor MHCII+/+ APCs pulsed with OVA(323–339) produced the same signal. We also tracked the fluorescent signal in OTII-DC cultures in vitro and detected that it was concentrated at the synapse over time. Altogether our findings suggest that tetracysteine tagged peptides can be used for tracking peptide-MHCII complexes during the interactions of primary mouse T cells and APCs and have the potential to be an alternative to MHCII tetramers to detect antigen specific T cells.

Tregs orchestrate antigen specific suppression via stripping cognate peptide-MHCII from the DC surface

Tregs are professional suppressors of the immune response, yet their mechanism of action in vivo remains unclear. We compared the morphology and stoichiometry of the interactions of activated 5CC7 T cells and 5CC7 iTregs with MCC88–103 pulsed splenic DCs by electron and confocal microscopy. Image analyses revealed that Tregs interacting with DC displayed a distinct morphology with finger like membrane projections at the DC binding site and uropods at the rear end within three hours of in vitro culture. In contrast, activated T cells maintained their round morphology. Tregs occupied a greater extent of the DC surface than activated T cells consistent with a higher binding avidity. Dynamic intravital two-photon microscopy of adoptively transferred OTII iTregs and activated OTII cells demonstrated that Treg displayed a greater volume and duration of contact with OVA323–339 pulsed DC compared to that of activated OTII cells. Subsequent to their high avidity interactions with DC, 5CC7 iTregs captured MCC88–103-I-Ek complexes from DC surface reducing the amount of MCC presented on DC. Reduced antigen presentation was not due to global suppression of the DC’s ability to present antigen as 5CC7 and 3A9 iTregs only captured their cognate peptide-MHCII from MCC/HEL double pulsed DC, reducing the DC presentation in an antigen specific manner. When double pulsed DCs were cultured with iTregs specific for one peptide, separated from the iTregs, the DC failed to prime T cells specific for the antigen seen by the iTreg, but primed T cells specific for the second antigen. Altogether, we propose antigen specific depletion of peptide-MHCII complexes as a new mechanism for Treg-mediated suppression.

Toll-like receptor 9 antagonizes antibody affinity maturation

Key events in T cell-dependent antibody responses, including affinity maturation, are dependent on the B cell’s presentation of antigen to helper T cells at critical check points in germinal center formation in secondary lymphoid organs. Here we show that Toll-like receptor 9 (TLR9) signaling blocked the ability of antigen-specific B cells to capture, process and present antigen and to activate antigen-specific helper T cells in vitro. In a mouse model in vivo and in a human clinical trial the TLR9 agonist, CpG, enhanced the magnitude of the antibody response to a protein vaccine but failed to promote affinity maturation. Thus, TLR9 signaling may enhance antibody titers at the expense of the ability of B cells to engage in germinal center events that are highly dependent on B cells’ antigen capture and presentation.

T cell-dependent antigen adjuvanted with DOTAP-CpG-B but not DOTAP-CpG-A induces robust germinal center responses and high affinity antibodies in mice

The development of vaccines for infectious diseases for which we currently have none, including HIV, will likely require the use of adjuvants that strongly promote germinal center responses and somatic hypermutation to produce broadly neutralizing antibodies. Here we compared the outcome of immunization with the T-cell dependent antigen, NP-conjugated to chicken gamma globulin (NP-CGG) adjuvanted with the toll-like receptor 9 (TLR9) ligands, CpG-A or CpG-B, alone or conjugated with the cationic lipid carrier, DOTAP. We provide evidence that only NP-CGG adjuvanted with DOTAP-CpG-B was an effective vaccine in mice resulting in robust germinal center responses, isotype switching and high affinity NP-specific antibodies. The effectiveness of DOTAP-CpG-B as an adjuvant was dependent on the expression of the TLR9 signaling adaptor MyD88 in immunized mice. These results indicate DOTAP-CpG-B but not DOTAP-CpG-A is an effective adjuvant for T cell-dependent protein antigen-based vaccines.

B Cells Produce Type 1 IFNs in Response to the TLR9 Agonist CpG-A Conjugated to Cationic Lipids

B cells express the innate receptor, TLR9, which signals in response to unmethylated CpG sequences in microbial DNA. Of the two major classes of CpG-containing oligonucleotides, CpG-A appears restricted to inducing type 1 IFN in innate immune cells and CpG-B to activating B cells to proliferate and produce Abs and inflammatory cytokines. Although CpGs are candidates for adjuvants to boost innate and adaptive immunity, our understanding of the effect of CpG-A and CpG-B on B cell responses is incomplete. In this study we show that both CpG-B and CpG-A activated B cells in vitro to proliferate, secrete Abs and IL-6, and that neither CpG-B nor CpG-A alone induced type 1 IFN production. However, when incorporated into the cationic lipid, DOTAP, CpG-A, but not CpG-B, induced a type 1 IFN response in B cells in vitro and in vivo. We provide evidence that differences in the function of CpG-A and CpG-B may be related to their intracellular trafficking in B cells. These findings fill an important gap in our understanding of the B cell response to CpGs, with implications for the use of CpG-A and CpG-B as immunomodulators.

A single nucleotide polymorphism in an AP2 transcription factor encoded in the malaria-causing Plasmodium berghei alters the development of host immunity

The Apetela2 (AP2) family of transcription factors is a major regulator of Plasmodium parasite gene expression. Twenty seven members of this family have been identified since their discovery in 2005. However, our understanding which AP2 members regulate key features of Plasmodium biology is incomplete. Here we describe the impact of a single nucleotide polymorphism (SNP) in the active site of the AP2 protein, PBANKA_011210, on the outcome of infection in mice. Plasmodium berghei Anka (PbA), the only rodent parasite that causes experimental cerebral malaria (ECM), codes for a phenylalanine at position 1823 whereas all other Plasmodium parasite strains, none of which cause ECM in mice, including PbNK65, have a serine in this position. Using CRISPR, we modified the PbNK65 parasite (PbNK65-WT) to encode the PbA SNP (PbNK65-PbA). The course of infection with PbNK65-WT or PbNK65-PbA were similar and showed no ECM pathology indicating that the PbA AP2 SNP is not sufficient to cause ECM. However, mice infected with PbNK65-PbA generated dramatically higher germinal center responses and produced higher titers of parasite-specific antibodies. When infected mice were treated with sub-therapeutic doses of the anti-malarial, chloroquine, to lower the parasitemias PbNK65-PbA-infected mice cleared the infection whereas mice infected with PbNK65-WT were unable to control the infection resulting severe anemia and death. These results reveal a novel role of AP2 proteins in controlling host immunity to Plasmodium infections.

Unique interaction dynamics and peptide-MHC class II (pMHC II) transendocytosis lead to antigen-specific T regulatory cell (Treg)-mediated suppression

Tregs can employ numerous mechanisms for inhibiting immune responses. Antigen-specific Tregs exhibit enhanced capacity to suppress compared to polyclonal Tregs, but unique suppressor mechanisms used by antigen-specific Tregs have not been elucidated. We first compared the interaction of antigen-specific induced Tregs (iTregs) and antigen-specific T effector cells with dendritic cells (DC) using scanning electron microscopy and intravital two-photon microscopy. Antigen-specific iTregs uniquely and rapidly formed dense clusters around DC suggesting that they may prevent the access of antigen-specific CD4+ T cells to the DC surface. In an adoptive transfer model, this rapid interaction was accompanied by a decreased ability of co-transferred naïve T cells to interact with the DCs as indicated by their failure to decrease their motility. More importantly, antigen-specific iTregs were found to specifically transendocytose cognate peptide-MHCII complexes from the DC surface to a greater extent than T effector cells resulting in diminished levels of antigen on the DC surface. Transmission electron microscopy of DC-Treg co-cultures showed that Tregs engulfed parts of DC processes as membrane invaginations within two hours and then internalized the p-MHCII complexes into endosomal vesicles. Taken together, these results indicate a two-step process by which antigen-specific Tregs inhibit antigen presentation. They rapidly and efficiently adhere to the DC surface and then deplete the pMHC II complexes from the DC resulting in potent suppression of the capacity of the DC to activate antigen-specific T cells.

The Toll-like receptor ligand CpG-A induces type 1 interferons in B cells contrasting the proinflammatory inducing activity of CpG-B

B cells express the innate immune system receptor, Toll like receptor 9 (TLR9), a potent regulator of B cell function, that signals in response to unmethylated CpG sequences in microbial DNA. A dichotomy in the function of the two major classes of CpG-containing oligonucleotides, namely CpG-A and CpG-B, appears to exist with CpG-A restricted to inducing type 1 interferon (type 1 IFN) in innate immune cells and CpG-B to activating B cells to proliferate and produce antibody and inflammatory cytokines. Although CpGs are candidates for adjuvants to boost the innate and adaptive immunity, our understanding of the effect of CpG-A and CpG-B on B cell responses is incomplete. We provide evidence that CpG-A activated B cells in vitro in a TLR9 dependent fashion resulting in the production of IL-6, proliferation, and alterations in the expression of a variety of B cell surface markers, albeit in a less robust fashion as compared to CpG-B. Neither CpGB nor CpG-A alone induced B cells to express type 1 IFN. However, when incorporated into the cationic lipid, DOTAP, CpG-A, but not CpG-B induced a robust type 1 IFN response in B cells both in vitro and in vivo. Conversely, CpG-B-DOTAP but not CpGA-DOTAP promoted B cell germinal center responses in vivo and the production of high affinity antibodies. We also provide evidence that difference in the function of CpGs versus DOTAP-associated-CpGs may be related to their intracellular trafficking in B cells since DOTAP enhances the trafficking of CpG-B but not CpG-A to late endosomal compartments. These findings have important implications for the use of CpG-A and CpG-B to augment type 1 IFN production versus B cell responses in vivo.

Toll-like receptor 9 signaling antagonizes antigen-specific B cell-helper T cell interactions

Key events in T cell-dependent antibody responses are dependent on the ability of B cells to capture antigen and process and present it to follicular helper T cells. Despite its importance, little is known about the regulation of this critical B cell function. Here we focus on the impact of signaling through the innate immune receptor, Toll like receptor 9 (TLR9), on the outcome of a B cell’s encounter with antigen. We show that although TLR9 signaling induced B cell proliferation, and secretion of cytokines and IgM, it blocked the ability of antigen-specific B cells to capture, process and present antigen. In the presence of the TLR9 agonist, CpG, B cells were less able to form synapses with antigen-containing membranes and to pull antigen from them. CpG also diminished the ability of the BCR to traffick antigen within the cell to antigen processing compartments resulting in fewer MHC-peptide complexes on the B cell surface. TLR signaling also antagonized the BCR-induced increases in the expression of both MHC class II and important co-receptors, including CD86, resulting in a decrease in the duration of antigen-specific B cell-T helper cell interaction and the inability of B cells to activate antigen-specific T cells. Chimeric mice that contained either wild type B cells or B cells deficient in TLR signaling when immunized with antigen adjuvanted with CpG showed that the loss of the B cells’ ability to respond to CpG resulted in lower antigen-specific IgM responses but enhanced high affinity antigen-specific IgG responses. Thus, B cell intrinsic TLR9 signaling may ensure rapid B cell expansion and antibody secretion at the expense of the ability of B cells to engage in germinal center events that are highly dependent antigen capture and presentation.

Application of super-resolution microscopy to the study of B and T lymphocyte mitochondria morphology and metabolism

High-resolution microscopy techniques have advanced our understanding of lymphocyte biology. An emerging focus in the field of immunometabolism on activation-induced metabolic reprogramming and its effects on immune cell function will require in-depth analyses of mitochondria. However, even with newer imaging technologies, obtaining super-resolution images of lymphocyte mitochondria remains challenging due to their small cytoplasmic sizes. Here, we compared standard confocal laser microscopy with three commonly used super-resolution methods to analyze activation-induced mitochondrial changes in B and T cells. Naïve B cells were stimulated in vitro via Toll-like receptor 9 and/or the B cell receptor, and naïve T cells were differentiated in vitro into activated or T regulatory phenotypes. The cells were imaged using standard laser confocal microscopy, AiryScan, stimulated emission depletion (STED) microscopy, and computerized tomography electron microscopy (TEM). Mitochondrial morphology was best resolved by staining both the mitochondrial membrane and matrix simultaneously. In preliminary analyses, we observed activation-induced changes in the distribution of lymphocyte mitochondria. Of the imaging methods used, only TEM allowed for 3D reconstructions of the mitochondria’s internal structure, which revealed swelling of the inner matrix and significant loss of cristae in B cells, but not in T cells. In conclusion, the super-resolution light microscopy techniques we developed appear to be powerful tools for immunometabolism studies of lymphocyte mitochondria, having demonstrated clear visualization even at the molecular level, while TEM answered key questions about intra-mitochondrial morphology.

Ex-vivo iTreg differentiation revisited: Convenient alternatives to existing strategies

Ex-vivo differentiation of regulatory T cells (Tregs) from naïve CD4⁺ T-cells has been widely used in immunological research. Isolation of a highly pure naïve T cell population is the key factor that determines the efficiency of subsequent Treg differentiation. Currently, this step relies mostly on FACS sorting, which is often costly, time consuming, and inconvenient. Alternatively, magnetic separation of T-cells can be performed; yet, available protocols fail to reach sort level purity and consequently result in low Treg differentiation efficiency. Here, we present the results of a comprehensive side-by-side comparison of various magnetic separation strategies and FACS sorting in multiple levels. Additionally, we propose a novel optimized custom made magnetic separation protocol, which not only yields sort level purity and Treg differentiation but also lowers the reagent costs up to 75% compared to the commercially available purification kits. The highly pure naïve CD4⁺ T-cell population obtained by this versatile method can also be used for differentiation of other T-cell subsets; therefore this protocol may have broad applications in T-cell research.

An Optimized Protocol to Analyze Glycolysis and Mitochondrial Respiration in Lymphocytes

Lymphocytes respond to a variety of stimuli by activating intracellular signaling pathways, which in turn leads to rapid cellular proliferation, migration and differentiation, and cytokine production. All of these events are tightly linked to the energy status of the cell, and therefore studying the energy-producing pathways may give clues about the overall functionality of these cells. The extracellular flux analyzer is a commonly used device for evaluating the performance of glycolysis and mitochondrial respiration in many cell types. This system has been used to study immune cells in a few published reports, yet a comprehensive protocol optimized particularly for lymphocytes is lacking. Lymphocytes are fragile cells that survive poorly in ex vivo conditions. Oftentimes lymphocyte subsets are rare, and working with low cell numbers is inevitable. Thus, an experimental strategy that addresses these difficulties is required. Here, we provide a protocol that allows for rapid isolation of viable lymphocytes from lymphoid tissues, and for the analysis of their metabolic states in the extracellular flux analyzer. Furthermore, we provide results of experiments in which the metabolic activities of several lymphocyte subtypes at different cell densities were compared. These observations suggest that our protocol can be used to achieve consistent, well-standardized results even at low cell concentrations, and thus it may have broad applications in future studies focusing on the characterization of metabolic events in immune cells.

The Regulation of Inherently Autoreactive VH4-34-Expressing B Cells in Individuals Living in a Malaria-Endemic Area of West Africa

Plasmodium falciparum malaria is a deadly infectious disease in which Abs play a critical role in naturally acquired immunity. However, the specificity and nature of Abs elicited in response to malaria are only partially understood. Autoreactivity and polyreactivity are common features of Ab responses in several infections and were suggested to contribute to effective pathogen-specific Ab responses. In this article, we report on the regulation of B cells expressing the inherently autoreactive VH4-34 H chain (identified by the 9G4 mAb) and 9G4⁺ plasma IgG in adults and children living in a P. falciparum malaria-endemic area in West Africa. The frequency of 9G4⁺ peripheral blood CD19⁺ B cells was similar in United States adults and African adults and children; however, more 9G4⁺ B cells appeared in classical and atypical memory B cell compartments in African children and adults compared with United States adults. The levels of 9G4⁺ IgG increased following acute febrile malaria but did not increase with age as humoral immunity is acquired or correlate with protection from acute disease. This was the case, even though a portion of 9G4⁺ B cells acquired phenotypes of atypical and classical memory B cells and 9G4⁺ IgG contained equivalent numbers of somatic hypermutations compared with all other VHs, a characteristic of secondary Ab repertoire diversification in response to Ag stimulation. Determining the origin and function of 9G4⁺ B cells and 9G4⁺ IgG in malaria may contribute to a better understanding of the varied roles of autoreactivity in infectious diseases.

Microfracture technique versus carbon fibre rod implantation for treatment of knee articular cartilage lesions

PURPOSE

To compare the microfracture technique with carbon fibre rod implantation for treatment of knee articular cartilage lesions.

METHODS

10 men and 30 women aged 22 to 56 (mean, 37.4) years underwent microfracture (n=20) or carbon fibre rod implantation (n=20) for International Cartilage Repair Society grade 3 to 4 knee articular cartilage lesions after a mean of 12.2 months of viscosupplementation and physiotherapy. Clinical outcome at 6 and 12 months was assessed using the Tegner-Lysholm score and modified Cincinnati score. Magnetic resonance imaging (MRI) outcome at 12 months was assessed by a radiologist. The modified magnetic resonance observation of cartilage repair tissue (MOCART) score was evaluated.

RESULTS

The 2 groups were comparable in terms of age, body mass index, lesion location, lesion size, duration of symptoms, and coexisting pathology. The microfracture group had a higher preoperative Tegner-Lysholm score (39.4±7.3 vs. 34.4±4.9, p=0.015) and modified Cincinnati score (36.4±7.2 vs. 30.4±4.0, p=0.002) than the carbon fibre rod group. At 12 months, change in both scores was significant within each group (p<0.001) and was higher in the microfracture than carbon fibre rod group (p<0.001). MRI showed minimal regenerative tissue. Lobulation, oedema, and hypertrophy were more commonly found in the regeneration tissue after carbon fibre rod implantation than microfracture. At 12 months, the MOCART score was higher in the microfracture than carbon fibre rod group (59 vs. 47, p<0.001).

CONCLUSION

Microfracture is superior to carbon fibre rod implantation in terms of clinical and radiological outcome.

A Simple, Versatile Antibody-Based Barcoding Method for Flow Cytometry

Barcoding of biological samples is a commonly used strategy to mark or identify individuals within a complex mixture. However, cell barcoding has not yet found wide use in flow cytometry that would benefit greatly from the ability to analyze pooled experimental samples simultaneously. This is due, in part, to technical and practical limitations of current fluorescent dye-based methods. In this study, we describe a simple, versatile barcoding strategy that relies on combinations of a single Ab conjugated to different fluorochromes and thus in principle can be integrated into any flow cytometry application. To demonstrate the efficacy of the approach, we describe the results of a variety of experiments using live cells as well as fixed and permeabilized cells. The results of these studies show that Ab-based barcoding provides a simple, practical method for identifying cells from individual samples pooled for analysis by flow cytometry that has broad applications in immunological research.

Toll-like receptor 9 signaling antagonizes the B cell receptor-dependent ability of B cells to process and present antigen to helper T cells

B cells express both an adaptive antigen-specific B cell receptor (BCR) and innate Toll-like receptors (TLRs) allowing the functional outcome of the B cell’s engagement with antigen to be modulated in response to pathogen-derived TLR ligands. In T cell-dependent responses, the BCR both signals for B cell proliferation and differentiation and also internalizes bound antigen for processing and presentation to helper T cells. Here we show that although the presence of the TLR9 ligand, CpG, does not affect early BCR mediated events following antigen binding including phosphorylation of key components of the signaling cascade and the formation of BCR clusters on cell surface, CpG alters the outcome of BCR signaling, resulting in unique transcriptional profiles, enhanced proliferation and differentiation to antibody secreting cells. In contrast, CpG dramatically limits the ability of B cells to process and present antigen to helper T cells. In the presence of CpG, BCR-induced upregulation of CD86 and MHC class II expressions are antagonized and antigen internalized by the BCR is not properly trafficked to antigen processing compartments resulting in reduced numbers of peptide-MHC class II complexes on the B cell surface. Indeed, CpG treated antigen-specific B cells show a reduced ability to maintain contact with antigen-specific T cells and to activate antigen-specific helper T cell proliferation in vitro. These results suggest that TLR9 activation in T cell dependent responses would drive B cell toward proliferation and antibody secretion and away from events that are highly dependent on the ability of B cells to present antigen to helper T cells, such as entry into germinal centers and affinity selection.

B cells have bifurcated Toll-like receptor signaling allowing both inflammatory cytokine and type 1 interferon responses

B cells express the endosomal, DNA sensing, Toll-like receptor 9 (TLR9) that, in response to CpG oligonucleotides, signals through the adaptor protein MyD88 and activates the NF-kB pathway leading to the transcriptional activation of proinflammatory cytokines. In dendritic cells TLR9-MyD88 signaling is bifurcated into two distinct pathways, the NF-kB pathway and an IRF7-dependent pathway that results in the activation of type 1 interferon (IFN) genes. In these cells, monomeric CpG-B activates the NF-kB-dependent pathway and multimeric CpG-A or CpG-A coupled to the liposomal transfection reagent, Dotap (CpG-A-Dotap), activates the IRF-7-dependent pathway. Here we provide evidence that the B cell TLR9 signaling pathway is similarly bifurcated. Both CpG-B and CpG-B-Dotap potently activate the NF-kB-dependent pathway leading to IL-6 synthesis but neither trigger an IFN response. In contrast, CpG-A-Dotap but not CpG-A alone stimulates an IFN response as shown by increases in the levels of mRNA encoding IFN and in the amount of IFN protein produced and also by the activation of B cells from IFN-reporter mice both in vitro and in vivo. By confocal microscopy CpG-A and CpG-B appear to traffic to different intracellular vesicles. However, the cellular machinery that mediates the IL-6 and IFN pathways seems to be linked in that pretreatment of B cells with CpG-B blocks the subsequent activation of the IFN pathway by CpG-A-Dotap. It will be of interest to determine if natural DNA containing ligands might trigger the two pathways in B cells.

Antigen-specific induced T regulatory cells (iTregs) inhibit dendritic cell (DC) function by capturing peptide-MHCII complexes from the DC surface

Tregs are critical mediators of peripheral immune tolerance. A majority of the mechanisms utilized by antigen-specific Tregs to suppress immune responses, suggest an initial inhibition of dendritic cell (DC) function that results in diminished activation of T effector cells (Teff) specific for the homologous target as well as diminished activation of other antigen-specific Teff cells that recognize different antigens presented by the same DC (bystander suppression). In an adoptive transfer model in vivo, we demonstrated that OTII transgenic iTregs specific for Ovalbumin323–339 markedly inhibited the expansion of OTII Teff, but did not inhibit the expansion of co-transferred SMARTA Teff (specific for LCMV NP61–76) even though the transferred DCs displayed both peptides. Analysis of iTreg-DC co-cultures in vitro using flow cytometry and confocal microscopy demonstrated that specific peptide-MHCII complexes were captured and internalized by iTregs leaving DCs with decreased levels of antigen. Polyclonal iTregs, naïve, and activated antigen-specific Teff did not capture peptide-MHCII complexes. Intravital microscopy of the popliteal lymph node showed that adoptively transferred OTII iTregs made larger clusters around the DC for a longer period of time compared to activated Teff and increased the speed of co-transferred naïve OTII Teff cells. Taken together these studies suggest that antigen-specific iTregs inhibit immune responses locally in an antigen-dependent fashion by forming firm interactions with DCs leading to a stripping of peptide-MHCII complexes from the DC surface by a transendocytosis-based mechanism.

Dynamic imaging of a Tbet-Foxp3 double reporter in the course of Th1 mediated immune response

T cells can integrate various environmental cues and acquire different transcription profiles through the differentiation processes. The transcription factor T-bet is switched on by CD4+ T cells during type 1 inflammation and acts as the master regulator of Th1 lineage of T cell differentiation and function. Strong Th1 responses are usually elicited by intracellular pathogens and must be counterbalanced by Foxp3+ Treg cells to prevent immunopathology. Recently, it was demonstrated that T-bet-deficient Treg cells fail to rescue Foxp3-deficient mice from Th1 cell-mediated inflammatory disease raising the questions how and why Tregs adapt the unique Th1 type transcription profile. Using a TbetZsGreen-Foxp3-RFP double reporter mouse model, we have addressed those questions by confocal microscopy of the live tissue sections, intravital microscopy of the popliteal lymph node and flow cytometry. We have demonstrated that Tregs in the T cell areas of the lymph node co-localized with Tbet expressing cells forming large clusters especially at the T cell-B cell border. B cell area also contained T-bet expressing cells both at the steady state and during type 1 inflammation, which were more sparse and moved remarkably faster compared to the T-bet expressing cells in the T cell area. Altogether, this suggests that Tregs are localized in close proximity to T-bet expressing cells in the live lymph nodes and may modulate their movement characteristics. The functional relevance of this needs to be further explored.

Herpesvirus orthologues of CD200 bind host CD200R but not related activating receptors

Several herpesviruses have acquired the gene for the CD200 membrane protein from their hosts and can downregulate myeloid activity through interaction of this viral CD200 orthologue with the host receptor for CD200, namely CD200R, which can give inhibitory signals. This receptor is a 'paired receptor', meaning proteins related to the inhibitory CD200R are present but differ in that they can give activating signals and also give a negligible interaction with CD200. We showed that the viral orthologues e127 from rat cytomegalovirus and K14 from human herpesvirus 8 do not bind the activating CD200R-like proteins from their respective species, although they do bind the inhibitory receptors. It is thought that the activating receptors have evolved in response to pathogens targeting the inhibitory receptor. In this case, the CD200 orthologue is not trapped by the activating receptor but has maintained the specificity of the host from which it was acquired, suggesting that the activating members of the CD200R family have evolved to protect against a different pathogen.

The prevalence and clinical characteristics of mitral valve prolapse in a large population-based epidemiologic study: the MELEN study

OBJECTIVE

Mitral valve prolapse (MVP) is the most common cardiac valvular abnormality in industrialized countries. Its prevalence has been estimated to be between 2% to 4%. However, some studies found the prevalence of MVP less than 1% which is significantly lower than the prevalence reported in the Framingham Heart Study. The purpose of this study was to determine the prevalence, demographic, clinical and echocardiographic characteristics of MVP in a large population-based epidemiologic study.

PATIENTS AND METHODS

The final cohort included 2,228 participants. Data were obtained by a validated questionnaire, physical examination of the cardiovascular system, recording of a resting electrocardiogram, transthoracic echocardiographic examination.

RESULTS

The echocardiographic prevalence of MVP was 0.36%. Baseline demographic and clinical characteristics of patients were as follows; 12.5% had hypertension, 37.5% had depression, 12.5% had migraine, 12.5% had diabetes mellitus, 12.5% had diastolic dysfunction, 25% had multi-nodular goiter, 12.5% had diffuse goiter and 25% had hyperthyroidism. During the follow-up of 36 months no major adverse events occurred in patients with MVP during the follow-up.

CONCLUSIONS

This finding suggests that MVP is a benign disorder and the prevalence of MVP is lower than previously studies. There might be a relationship between MVP and goiter, and depression.

Inhibiting the mammalian target of rapamycin as an adjunctive therapy for cerebral malaria (MPF7P.714)

Malaria is an infectious disease caused by parasites of the Plasmodium spp. In endemic areas, in approximately 1% of cases, almost exclusively in young children, malaria becomes severe resulting in nearly seven hundred thousand deaths each year in Africa alone. Cerebral malaria (CM) is a common form of severe malaria and one for which we have no effective adjunctive therapy. The kinase, mammalian target of rapamycin (mTOR), through its regulation of cellular metabolism, is a central regulator of immune responses and drugs that inhibit the mTOR pathway have been shown to be antiparasitic, raising the possibility that mTOR inhibitors could be effective adjunctive therapies for CM. Here we show in a mouse model of CM, experimental CM (ECM), that the mTOR inhibitor rapamycin protects against ECM when administered within the first four days of infection. Treatment with rapamycin increased survival, blocked breakdown of the blood brain barrier and brain hemorrhaging, decreased influx of both CD4+ and CD8+ T cells into the brain and the accumulation of parasitized red blood cells in the brain. Remarkably, animals were protected against ECM even though rapamycin treatment significantly increased the inflammatory response induced by infection in both the brain and spleen and elevated the levels of peripheral parasitemia. These results open a new avenue for the development of highly selective adjunctive therapies for CM, by targeting pathways that regulate host and parasite metabolism.