Remembrance of immunology past: conversations with Herman Eisen.

Herman Eisen and Sondra Schlesinger spent several days together in September 2007 in Woods Hole, Massachusetts, talking about immunology, focusing on his remembrances of the field over the more than 60 years of his involvement. This article is an abridged version of those discussions (the full version is available on the Annual Reviews website). It is both an oral history and a written memory of some important but selected areas of immunology.

Manipulating the selection forces during affinity maturation to generate cross-reactive HIV antibodies.

Generation of potent antibodies by a mutation-selection process called affinity maturation is a key component of effective immune responses. Antibodies that protect against highly mutable pathogens must neutralize diverse strains. Developing effective immunization strategies to drive their evolution requires understanding how affinity maturation happens in an environment where variants of the same antigen are present. We present an in silico model of affinity maturation driven by antigen variants which reveals that induction of cross-reactive antibodies often occurs with low probability because conflicting selection forces, imposed by different antigen variants, can frustrate affinity maturation. We describe how variables such as temporal pattern of antigen administration influence the outcome of this frustrated evolutionary process. Our calculations predict, and experiments in mice with variant gp120 constructs of the HIV envelope protein confirm, that sequential immunization with antigen variants is preferred over a cocktail for induction of cross-reactive antibodies focused on the shared CD4 binding site epitope.

The role of chloroplast movement in C4 photosynthesis: a theoretical analysis using a three-dimensional reaction-diffusion model for maize.

Chloroplasts movement within mesophyll cells in C4 plants is hypothesized to enhance the CO2 concentrating mechanism, but this is difficult to verify experimentally. A three-dimensional (3D) leaf model can help analyse how chloroplast movement influences the operation of the CO2 concentrating mechanism. The first volumetric reaction-diffusion model of C4 photosynthesis that incorporates detailed 3D leaf anatomy, light propagation, ATP and NADPH production, and CO2, O2 and bicarbonate concentration driven by diffusional and assimilation/emission processes was developed. It was implemented for maize leaves to simulate various chloroplast movement scenarios within mesophyll cells: the movement of all mesophyll chloroplasts towards bundle sheath cells (aggregative movement) and movement of only those of interveinal mesophyll cells towards bundle sheath cells (avoidance movement). Light absorbed by bundle sheath chloroplasts relative to mesophyll chloroplasts increased in both cases. Avoidance movement decreased light absorption by mesophyll chloroplasts considerably. Consequently, total ATP and NADPH production and net photosynthetic rate increased for aggregative movement and decreased for avoidance movement compared with the default case of no chloroplast movement at high light intensities. Leakiness increased in both chloroplast movement scenarios due to the imbalance in energy production and demand in mesophyll and bundle sheath cells. These results suggest the need to design strategies for coordinated increases in electron transport and Rubisco activities for an efficient CO2 concentrating mechanism at very high light intensities.

A Dutch Pre-DSM Attempt at Psychiatric Classification.

Considering the growing sense of ambivalence about the merits of the DSM, the time seems right for the re-evaluation of nosological attempts and efforts in the pre-DSM era. One example of these attempts is the CHAM system developed by the Dutch psychiatrist R.M. Silbermann (1932-1976). This system is intended as a simple classification with 20 "psychiatric states," which are classified based on the presence of one of 12 hierarchically arranged core symptoms or key characteristics, while all "hierarchically higher" symptoms are excluded without inference about the "hierarchically lower" symptoms. Its scientific evidence is, as yet, insufficiently substantiated. However, disqualifying the CHAM system as an outdated Dutch folklore is like throwing out the baby with the bathwater. The CHAM system emerges as clinically straightforward, didactically fruitful, and consistent with more modern initiatives in descriptive psychopathology. Studying pre-DSM attempts such as Silbermann's CHAM system can stimulate psychopathological thinking and serve as a source of inspiration for future phenomenological research in psychiatry.

Treatment of sarcoptic and chorioptic mange in an alpaca (Vicugna pacos) herd with a combination of topical amitraz and subcutaneous ivermectin.

Clinical history: An outbreak of intense pruritus and weight loss in a herd of 40 alpacas (Vicugna pacos) in the south-west of France was investigated after the death of 14 adults. One alpaca was referred to a veterinary teaching hospital for diagnosis and treatment but died soon after and one of the dead alpacas was submitted for necropsy. Clinical findings: The remaining alpacas were intensely pruritic with variably severe and extensive alopecia, erythema, lichenification and crusting on the face, ventral abdomen and distal limbs. Superficial skin scrapes from five animals revealed large numbers of Sarcoptes scabiei mites, and less frequent and numerous Chorioptes bovis mites. Coproscopic examinations revealed a median of 1,350 (min 500, max 8800) strongyle epg. The alpaca admitted for treatment was anaemic and hypoalbuminaemic. Skin scrapes revealed copious S. scabiei and C. bovis mites. The two alpacas examined post-mortem had similar skin lesions to those examined on-farm and were cachexic. One had lung lesions attributed to protostrongylid infestation and its liver contained numerous Dicrocoelium spp. adults. Diagnosis: Sarcoptic and chorioptic mange with secondary superficial bacterial skin infection, associated with severe internal parasitism and underfeeding. Treatment and outcome: All 25 alpacas were treated topically with a 3% chlorhexidine shampoo followed by a 0.025% amitraz wash at the initial visit and then 1, 2, 3, 7 and 9 weeks later. A systemic treatment with S/C 500 µg/kg ivermectin was administered at the initial visit and then 2, 7 and 9 weeks later. The alpacas were treated orally with 50 mg/kg praziquantel to control dicrocoeliosis. Nutritional measures, including increased pasture area and supplemental feeding were simultaneously implemented. Pruritus was reduced 1 week after the start of treatment and had resolved after 2 weeks. After 9 weeks, skin lesions were markedly improved. Six months after the initial visit, skin lesions entirely resolved and superficial skin scrapes, taken from half of the animals, were negative for mites. Clinical relevance: This is the first report of the use of two acaricides combined with a chlorhexidine shampoo to successfully treat simultaneous sarcoptic and chorioptic mange in alpacas.

Using a reaction-diffusion model to estimate day respiration and reassimilation of (photo)respired CO2 in leaves.

Methods using gas exchange measurements to estimate respiration in the light (day respiration Rd ) make implicit assumptions about reassimilation of (photo)respired CO2 ; however, this reassimilation depends on the positions of mitochondria. We used a reaction-diffusion model without making these assumptions to analyse datasets on gas exchange, chlorophyll fluorescence and anatomy for tomato leaves. We investigated how Rd values obtained by the Kok and the Yin methods are affected by these assumptions and how those by the Laisk method are affected by the positions of mitochondria. The Kok method always underestimated Rd . Estimates of Rd by the Yin method and by the reaction-diffusion model agreed only for nonphotorespiratory conditions. Both the Yin and Kok methods ignore reassimilation of (photo)respired CO2 , and thus underestimated Rd for photorespiratory conditions, but this was less so in the Yin than in the Kok method. Estimates by the Laisk method were affected by assumed positions of mitochondria. It did not work if mitochondria were in the cytosol between the plasmamembrane and the chloroplast envelope. However, mitochondria were found to be most likely between the tonoplast and chloroplasts. Our reaction-diffusion model effectively estimates Rd , enlightens the dependence of Rd estimates on reassimilation and clarifies (dis)advantages of existing methods.

Gender Differences in Dental Anxiety and Medical Fear in Croatian Adolescents.

OBJECTIVES: The aim of this study was to differentiate anxious from nonanxious adolescents and evaluate gender differences in anxiety with respect to previous negative dental and medical experiences. The purpose was also to evaluate a causative relationship between child medical fear and dental anxiety. STUDY DESIGN: This study sampled 113 Croatian adolescents from 15 to18 years of age. Children's Fear Survey Schedule - Dental Subscale (CFSS-DS) was used for the assessment of child dental anxiety regarding visits to the dentist and receiving dental treatment. A modified version of Child Medical Fear Questionnaire (CMFQ-M) was used for evaluation of child medical fear related to medical treatment and doctors in general. RESULTS AND CONCLUSION: The results showed significantly higher dental anxiety (CFSS-DS) and medical fear (CMFQ-M) in adolscent girls (p<0,001) as compared to adolescent boys. A significantly strong correlation between medical fear and dental anxiety in adolescent girls was proved by Pearson's correlation coefficient (p < 0,01). In this study, CMFQ-M and CFSS-DS questionnaires were standardized in the Croatian adolescent population and proved reliable in the estimation of anxious behaviour with respect to specific medical and dental situations.

Persistent Antigen and Prolonged AKT-mTORC1 Activation Underlie Memory CD8 T Cell Impairment in the Absence of CD4 T Cells.

Recall responses by memory CD8 T cells are impaired in the absence of CD4 T cells. Although several mechanisms have been proposed, the molecular basis is still largely unknown. Using a local influenza virus infection in the respiratory tract and the lung of CD4(-/-) mice, we show that memory CD8 T cell impairment is limited to the lungs and the lung-draining lymph nodes, where viral Ags are unusually persistent and abundant in these mice. Persistent Ag exposure results in prolonged activation of the AKT-mTORC1 pathway in Ag-specific CD8 T cells, favoring their development into effector memory T cells at the expense of central memory T cells, and inhibition of mTORC1 by rapamycin largely corrects the impairment by promoting central memory T cell development. The findings suggest that the prolonged AKT-mTORC1 activation driven by persistent Ag is a critical mechanism underlying the impaired memory CD8 T cell development and responses in the absence of CD4 T cells.

Three-dimensional microscale modelling of CO2 transport and light propagation in tomato leaves enlightens photosynthesis.

We present a combined three-dimensional (3-D) model of light propagation, CO2 diffusion and photosynthesis in tomato (Solanum lycopersicum L.) leaves. The model incorporates a geometrical representation of the actual leaf microstructure that we obtained with synchrotron radiation X-ray laminography, and was evaluated using measurements of gas exchange and leaf optical properties. The combination of the 3-D microstructure of leaf tissue and chloroplast movement induced by changes in light intensity affects the simulated CO2 transport within the leaf. The model predicts extensive reassimilation of CO2 produced by respiration and photorespiration. Simulations also suggest that carbonic anhydrase could enhance photosynthesis at low CO2 levels but had little impact on photosynthesis at high CO2 levels. The model confirms that scaling of photosynthetic capacity with absorbed light would improve efficiency of CO2 fixation in the leaf, especially at low light intensity.

Polyreactivity increases the apparent affinity of anti-HIV antibodies by heteroligation.

During immune responses, antibodies are selected for their ability to bind to foreign antigens with high affinity, in part by their ability to undergo homotypic bivalent binding. However, this type of binding is not always possible. For example, the small number of gp140 glycoprotein spikes displayed on the surface of the human immunodeficiency virus (HIV) disfavours homotypic bivalent antibody binding. Here we show that during the human antibody response to HIV, somatic mutations that increase antibody affinity also increase breadth and neutralizing potency. Surprisingly, the responding naive and memory B cells produce polyreactive antibodies, which are capable of bivalent heteroligation between one high-affinity anti-HIV-gp140 combining site and a second low-affinity site on another molecular structure on HIV. Although cross-reactivity to self-antigens or polyreactivity is strongly selected against during B-cell development, it is a common serologic feature of certain infections in humans, including HIV, Epstein-Barr virus and hepatitis C virus. Seventy-five per cent of the 134 monoclonal anti-HIV-gp140 antibodies cloned from six patients with high titres of neutralizing antibodies are polyreactive. Despite the low affinity of the polyreactive combining site, heteroligation demonstrably increases the apparent affinity of polyreactive antibodies to HIV.

Promiscuous binding of extracellular peptides to cell surface class I MHC protein.

Algorithms derived from measurements of short-peptide (8-10 mers) binding to class I MHC proteins suggest that the binding groove of a class I MHC protein, such as K(b), can bind well over 1 million different peptides with significant affinity (<500 nM), a level of ligand-binding promiscuity approaching the level of heat shock protein binding of unfolded proteins. MHC proteins can, nevertheless, discriminate between similar peptides and bind many of them with high (nanomolar) affinity. Some insights into this high-promiscuity/high-affinity behavior and its impact on immunodominant peptides in T-cell responses to some infections and vaccination are suggested by results obtained here from testing a model developed to predict the number of cell surface peptide-MHC complexes that form on cells exposed to extracellular (exogenous) peptides.

IL-21 receptor signalling partially mediates Th2-mediated allergic airway responses.

BACKGROUND: Interleukin-21 (IL-21) has been implicated in the development of Th2-mediated immune responses; however, the exact role it plays in allergic diseases is not well understood. OBJECTIVE: To elucidate the contribution of IL-21 receptor signalling to Th2-dependent immune responses in the lung. METHODS: We compared allergic airway responses in wild-type BALB/c and Il21r-deficient mice exposed to local airway challenge with house dust mite (HDM). RESULTS: We demonstrate that IL-21R-deficiency reduces HDM-driven airway hyperresponsiveness (AHR) with only partial effects on airway inflammation. Concomitant with the reduction in AHR in Il21r-deficient mice, significant suppression was observed in protein levels of the Th2 cytokines IL-4, and IL-13. In contrast, IL-21R-deficiency was associated with an increase in PBS- and allergen-driven IgE levels, while IgG1 and IgG2a levels were decreased. Moreover, our results suggest that IL-21 may contribute to AHR through its ability to both directly induce Th2 cell survival and to impair regulatory T-cell suppression of Th2 cytokine production. Importantly, we show that IL-21-positive cells are increased in the bronchial mucosa of asthmatics compared with non-asthmatics. CONCLUSION: These results suggest that IL-21 plays an important role in the allergic diathesis by enhancing Th2 cytokine production through multiple mechanisms including the suppression of Treg inhibitory effects on Th2 cell cytokine production.

Comparison of fracture resistance in post restorations in primary maxillary incisors.

AIM: This in vitro study aimed to test the fracture resistance of 4 different posts used in the restoration of severely decayed primary incisors. MATERIALS AND METHODS: Fifty primary incisors were selected for this study and sectioned 1 mm above the CEJ. After filing and irrigation of the root canal space, the canals were obturated with Metapex and 3 mm of post space was prepared inside the canals. Intact glass fiber posts, split-ended glass fiber posts, composite resin posts, and orthodontic γ 'gamma' wire posts were used as intracanal posts and the final composite resin restoration was placed using a paediatric strip crown. After thermocycling of the specimens, the fracture resistance was measured using a universal testing machine. RESULTS: The mean fracture resistance of split- ended glass fiber posts was higher than the other groups, however, there was no significant difference between any of the groups (P>0.05). CONCLUSION: Split-ended glass fiber posts seem to be a more appropriate option for full coverage restorations in primary incisors.

Indicators of dental anxiety in children just prior to treatment.

OBJECTIVES: We evaluated the relationship between child dental anxiety and selected child and parental characteristics. STUDY DESIGN: Children and their parents were interviewed at the New York University, College of Dentistry, Pediatric Dentistry Clinic. The Children's Fear Survey Schedule - Dental Subscale (CFSS-DS) evaluated child self-reported anxiety; the Modified Dental Anxiety Scale (MDAS) measured self-reported parental anxiety when the parent received dental treatment. RESULTS: Ninety-three children and their parents completed the questionnaires. Mean CFSS-DS scores were higher for girls than boys (32.5 vs. 26.3, p=0.003) and for children whose accompanying parents had MDAS scores of 11+ vs. ≥ 11 (32.8 vs. 26.6, p=0.001). There was little difference in mean CFSS-DS scores among those aged 6-10 yrs. vs. 11-14 yrs. (30.1 vs. 29.3). Significant correlations were found between CFSS-DS and both gender (Spearman's rho, rs=0.31) and MDAS scores (rs=0.33), but not between CFSS-DS and child age (rs=-0.05). Controlling simultaneously for gender, MDAS score and child age, a high CFSS-DS score (38+ vs. ≥ 38) was positively associated with girls (ORadj=3.76, 95% CI: 1.13-12.54) and an MDAS score of ≤ 15 vs. ≥ 11 (ORadj=2.50, 0.73-8.54), but weakly and inversely associated with age (ORadj=0.80, 0.25-2.52). CONCLUSION: Child gender and parental anxiety are indicators of child dental anxiety.

Daily bias-corrected weather data and daily simulated growth data of maize, millet, sorghum, and wheat in the changing climate of sub-Saharan Africa.

Crop models are the primary means by which agricultural scientists assess climate change impacts on crop production. Site-based and high-quality weather and climate data is essential for agronomically and physiologically sound crop simulations under historical and future climate scenarios. Here, we describe a bias-corrected dataset of daily agro-meteorological data for 109 reference weather stations distributed across key production areas of maize, millet, sorghum, and wheat in ten sub-Saharan African countries. The dataset leverages extensive ground observations from the Global Yield Gap Atlas (GYGA), an existing climate change projections dataset from the Inter-Sectoral Model Intercomparison Project (ISIMIP), and a calibrated crop simulation model (the WOrld FOod Studies -WOFOST). The weather data were bias-corrected using the delta method, which is widely used in climate change impact studies. The bias-corrected dataset encompasses daily values of maximum and minimum temperature, precipitation rate, and global radiation obtained from five models participating in the Sixth Phase of the Coupled Model Intercomparison Project (CMIP6), as well as simulated daily growth variables for the four crops. The data covers three periods: historical (1995-2014), 2030 (2020-2039), and 2050 (2040-2059). The simulation of daily growth dynamics for maize, millet, sorghum, and wheat growth was performed using the daily weather data and the WOFOST crop model, under potential and water-limited potential conditions. The crop simulation outputs were evaluated using national agronomic expertise. The presented datasets, including the weather dataset and daily simulated crop growth outputs, hold substantial potential for further use in the investigation of future climate change impacts in sub-Saharan Africa. The daily weather data can be used as an input into other modelling frameworks for crops or other sectors (e.g., hydrology). The weather and crop growth data can provide key insights about agro-meteorological conditions and water-limited crop output to inform adaptation priorities and benchmark (gridded) crop simulations. Finally, the weather and simulated growth data can also be used for training machine learning techniques for extrapolation purposes.

Interaction of streptavidin-based peptide-MHC oligomers (tetramers) with cell-surface TCRs.

The binding of oligomeric peptide-MHC (pMHC) complexes to cell surface TCR can be considered to approximate TCR-pMHC interactions at cell-cell interfaces. In this study, we analyzed the equilibrium binding of streptavidin-based pMHC oligomers (tetramers) and their dissociation kinetics from CD8(pos) T cells from 2C-TCR transgenic mice and from T cell hybridomas that expressed the 2C TCR or a high-affinity mutant (m33) of this TCR. Our results show that the tetramers did not come close to saturating cell-surface TCR (binding only 10-30% of cell-surface receptors), as is generally assumed in deriving affinity values (K(D)), in part because of dissociative losses from tetramer-stained cells. Guided by a kinetic model, the oligomer dissociation rate and equilibrium constants were seen to depend not only on monovalent association and dissociation rates (k(off) and k(on)), but also on a multivalent association rate (µ) and TCR cell-surface density. Our results suggest that dissociation rates could account for the recently described surprisingly high frequency of tetramer-negative, functionally competent T cells in some T cell responses.

Evolving concepts of specificity in immune reactions.

Our goal is to provide a perspective on current understanding of the origins of specificity in immune reactions, a topic that has intrigued scientists for over a century. A fundamental property of adaptive immune responses is the ability to discriminate among an immense variety of substances by means of antibodies (Abs) and Ab-like receptors on T lymphocytes [T-cell receptors (TCRs)], each able to bind a particular chemical structure [the antigen (Ag)] and not, or only weakly, similar alternatives. Evidence has long existed, however, and has grown, especially recently, that while exhibiting remarkable specificity, many individual Abs and TCRs can also bind a variety of very different ligands. How can Ag recognition by these receptors exercise the great specificity for which they are renowned and yet react with a variety of different ligands (degeneracy)? We critically consider the mechanistic bases for this specificity/degeneracy enigma and also compare and contrast Ag recognition by Abs and TCRs.

Antigen-bearing dendritic cells regulate the diverse pattern of memory CD8 T-cell development in different tissues.

Memory T cells of the effector type (T(EM)) account for the characteristic rapidity of memory T-cell responses, whereas memory T cells of the central type (T(CM)) account for long-lasting, vigorously proliferating memory T-cell responses. How antigen-stimulated (primed) T cells develop into different memory T-cell subsets with diverse tissue distributions is largely unknown. Here we show that after respiratory tract infection of mice with influenza virus, viral antigen associated with dendritic cells (DCs) was abundant in lung-draining lymph nodes (DLN) and the spleen for more than a week but was scant and transient in nondraining lymph nodes (NDLN). Correspondingly, activated CD8 T cells proliferated extensively in DLN and the spleen but minimally in NDLN. Strikingly, however, although most persisting CD8 T cells in DLN and spleen exhibited the T(EM) phenotype, those persisting in NDLN exhibited the T(CM) phenotype. Reducing antigen exposure by depleting DCs at the peak of primary T-cell responses enhanced the development of T(CM), whereas subjecting primed CD8 T cells from NDLN to additional antigen stimulation inhibited T(CM) development. These findings demonstrate that differences in persistence of antigen-bearing DCs in various tissues regulate the tissue-specific pattern of memory CD8 T-cell development. The findings have significant implications for design of vaccines and immunization strategies.

The impact of TCR-binding properties and antigen presentation format on T cell responsiveness.

TCR interactions with cognate peptide-MHC (pepMHC) ligands are generally low affinity. This feature, together with the requirement for CD8/CD4 participation, has made it difficult to dissect relationships between TCR-binding parameters and T cell activation. Interpretations are further complicated when comparing different pepMHC, because these can vary greatly in stability. To examine the relationships between TCR-binding properties and T cell responses, in this study we characterized the interactions and activities mediated by a panel of TCRs that differed widely in their binding to the same pepMHC. Monovalent binding of soluble TCR was characterized by surface plasmon resonance, and T cell hybridomas that expressed these TCR, with or without CD8 coexpression, were tested for their binding of monomeric and oligomeric forms of the pepMHC and for subsequent responses (IL-2 release). The binding threshold for eliciting this response in the absence of CD8 (K(D) = 600 nM) exhibited a relatively sharp cutoff between full activity and no activity, consistent with a switchlike response to pepMHC on APCs. However, when the pepMHC was immobilized (plate bound), T cells with the lowest affinity TCRs (e.g., K(D) = 30 microM) responded, even in the absence of CD8, indicating that these TCR are signaling competent. Surprisingly, even cells that expressed high-affinity (K(D) = 16 nM) TCRs along with CD8 were unresponsive to oligomers in solution. The findings suggest that to drive downstream T cell responses, pepMHC must be presented in a form that supports formation of appropriate supramolecular clusters.