Mutations that adapt SARS-CoV-2 to mink or ferret do not increase fitness in the human airway

SARS-CoV-2 has a broad mammalian species tropism infecting humans, cats, dogs, and farmed mink. Since the start of the 2019 pandemic, several reverse zoonotic outbreaks of SARS-CoV-2 have occurred in mink, one of which reinfected humans and caused a cluster of infections in Denmark. Here we investigate the molecular basis of mink and ferret adaptation and demonstrate the spike mutations Y453F, F486L, and N501T all specifically adapt SARS-CoV-2 to use mustelid ACE2. Furthermore, we risk assess these mutations and conclude mink-adapted viruses are unlikely to pose an increased threat to humans, as Y453F attenuates the virus replication in human cells and all three mink adaptations have minimal antigenic impact. Finally, we show that certain SARS-CoV-2 variants emerging from circulation in humans may naturally have a greater propensity to infect mustelid hosts and therefore these species should continue to be surveyed for reverse zoonotic infections.

Deep sequence analysis of HIV adaptation following vertical transmission reveals the impact of immune pressure on the evolution of HIV

Human immunodeficiency virus (HIV) can adapt to an individual’s T cell immune response via genomic mutations that affect antigen recognition and impact disease outcome. These viral adaptations are specific to the host’s human leucocyte antigen (HLA) alleles, as these molecules determine which peptides are presented to T cells. As HLA molecules are highly polymorphic at the population level, horizontal transmission events are most commonly between HLA-mismatched donor/recipient pairs, representing new immune selection environments for the transmitted virus. In this study, we utilised a deep sequencing approach to determine the HIV quasispecies in 26 mother-to-child transmission pairs where the potential for founder viruses to be pre-adapted is high due to the pairs being haplo-identical at HLA loci. This scenario allowed the assessment of specific HIV adaptations following transmission in either a non-selective immune environment, due to recipient HLA mismatched to original selecting HLA, or a selective immune environment, mediated by matched donor/recipient HLA. We show that the pattern of reversion or fixation of HIV adaptations following transmission provides insight into the replicative cost, and likely compensatory networks, associated with specific adaptations in vivo. Furthermore, although transmitted viruses were commonly heavily pre-adapted to the child’s HLA genotype, we found evidence of de novo post-transmission adaptation, representing new epitopes targeted by the child’s T cell response. High-resolution analysis of HIV adaptation is relevant when considering vaccine and cure strategies for individuals exposed to adapted viruses via transmission or reactivated from reservoirs.

Highly mutable pathogens utilise genetic variations within T cell epitopes as a mechanism of immune escape (viral adaptation). The diversity of the human leucocyte antigen (HLA) molecules that present viral targets to T cells in human populations partially protects against rapid population-level accumulation of human immunodeficiency virus (HIV) adaptations through horizontal transmissions. In contrast, vertical transmissions occur between haplo-identical mother/child pairs, and potentially include adaptive changes through father-mother-child transmission, representing a pathway to complete pre-adaptation to HLA alleles in child hosts over only two transmission events. We utilised next-generation sequencing to examine HIV evolution in the unique setting of vertical HIV transmission. We predict the in vivo replicative cost and immune benefit of specific HIV adaptations that could be used to inform vaccine design and cure strategies to combat viral immune adaptation.

A Return to Wisdom: Using Sickness Behaviors to Integrate Ecological and Translational Research

Sickness is typically characterized by fever, anorexia, cachexia, and reductions in social, pleasurable, and sexual behaviors. These responses can be displayed at varying intensities both within and among individuals, and the adaptive nature of sickness responses can be demonstrated by the context-dependent nature of their expression. The study of sickness has become an important area of investigation for researchers in a wide range of areas, including psychoneuroimmunology (PNI) and ecoimmunology (EI). The general goal of PNI is to identify key interactions among the nervous, endocrine and immune systems and behavior, and how disruptions in these processes might contribute to disease states. EI, in turn, has been established more recently within the perspectives of ecology and evolutionary biology, and is aimed more at understanding natural variation in immune function and sickness responses within a broadly integrative, organismal, and evolutionary context. The goal of this review is to examine the literature on sickness from both basic and biomedical perspectives within PNI and EI and to demonstrate how the integrative study of sickness behavior can serve as an integrating agent to connect ecological and translational approaches to the study of disease. By focusing on a set of specific exemplars, including the energetics of sickness, social context, and environmental influences on sickness, we hope to accomplish the larger goal of developing a common synthetic framework to understand sickness from multiple levels of analysis and varying perspectives across the fields of PNI and EI. By applying this integrative approach to sickness, we will be able to develop a more comprehensive view of sickness as a suite of adaptive responses rather than the simply deleterious consequences of illness.

Deciphering the biology of porcine epidemic diarrhea virus in the era of reverse genetics

Emergence of the porcine epidemic diarrhea virus (PEDV) as a global threat to the swine industry underlies the urgent need for deeper understanding of this virus. To date, we have yet to identify functions for all the major gene products, much less grasp their implications for the viral life cycle and pathogenic mechanisms. A major reason is the lack of genetic tools for studying PEDV. In this review, we discuss the reverse genetics approaches that have been successfully used to engineer infectious clones of PEDV as well as other potential and complementary methods that have yet to be applied to PEDV. The importance of proper cell culture for successful PEDV propagation and maintenance of disease phenotype are addressed in our survey of permissive cell lines. We also highlight areas of particular relevance to PEDV pathogenesis and disease that have benefited from reverse genetics studies and pressing questions that await resolution by such studies. In particular, we examine the spike protein as a determinant of viral tropism, entry and virulence, ORF3 and its association with cell culture adaptation, and the nucleocapsid protein and its potential role in modulating PEDV pathogenicity. Finally, we conclude with an exploration of how reverse genetics can help mitigate the global impact of PEDV by addressing the challenges of vaccine development.

Ethanolamine Signaling Promotes Salmonella Niche Recognition and Adaptation during Infection

Chemical and nutrient signaling are fundamental for all cellular processes, including interactions between the mammalian host and the microbiota, which have a significant impact on health and disease. Ethanolamine is an essential component of cell membranes and has profound signaling activity within mammalian cells by modulating inflammatory responses and intestinal physiology. Here, we describe a virulence-regulating pathway in which the foodborne pathogen Salmonella enterica serovar Typhimurium (S. Typhimurium) exploits ethanolamine signaling to recognize and adapt to distinct niches within the host. The bacterial transcription factor EutR promotes ethanolamine metabolism in the intestine, which enables S. Typhimurium to establish infection. Subsequently, EutR directly activates expression of the Salmonella pathogenicity island 2 in the intramacrophage environment, and thus augments intramacrophage survival. Moreover, EutR is critical for robust dissemination during mammalian infection. Our findings reveal that S. Typhimurium co-opts ethanolamine as a signal to coordinate metabolism and then virulence. Because the ability to sense ethanolamine is a conserved trait among pathogenic and commensal bacteria, our work indicates that ethanolamine signaling may be a key step in the localized adaptation of bacteria within their mammalian hosts.

Immune and stress responses in oysters with insights on adaptation

Oysters are representative bivalve molluscs that are widely distributed in world oceans. As successful colonizers of estuaries and intertidal zones, oysters are remarkably resilient against harsh environmental conditions including wide fluctuations in temperature and salinity as well as prolonged air exposure. Oysters have no adaptive immunity but can thrive in microbe-rich estuaries as filter-feeders. These unique adaptations make oysters interesting models to study the evolution of host-defense systems. Recent advances in genomic studies including sequencing of the oyster genome have provided insights into oyster's immune and stress responses underlying their amazing resilience. Studies show that the oyster genomes are highly polymorphic and complex, which may be key to their resilience. The oyster genome has a large gene repertoire that is enriched for immune and stress response genes. Thousands of genes are involved in oyster's immune and stress responses, through complex interactions, with many gene families expanded showing high sequence, structural and functional diversity. The high diversity of immune receptors and effectors may provide oysters with enhanced specificity in immune recognition and response to cope with diverse pathogens in the absence of adaptive immunity. Some members of expanded immune gene families have diverged to function at different temperatures and salinities or assumed new roles in abiotic stress response. Most canonical innate immunity pathways are conserved in oysters and supported by a large number of diverse and often novel genes. The great diversity in immune and stress response genes exhibited by expanded gene families as well as high sequence and structural polymorphisms may be central to oyster's adaptation to highly stressful and widely changing environments.

Group Selection and Contribution of Minority Variants during Virus Adaptation Determines Virus Fitness and Phenotype

Understanding how a pathogen colonizes and adapts to a new host environment is a primary aim in studying emerging infectious diseases. Adaptive mutations arise among the thousands of variants generated during RNA virus infection, and identifying these variants will shed light onto how changes in tropism and species jumps can occur. Here, we adapted Coxsackie virus B3 to a highly permissive and less permissive environment. Using deep sequencing and bioinformatics, we identified a multi-step adaptive process to adaptation involving residues in the receptor footprints that correlated with receptor availability and with increase in virus fitness in an environment-specific manner. We show that adaptation occurs by selection of a dominant mutation followed by group selection of minority variants that together, confer the fitness increase observed in the population, rather than selection of a single dominant genotype.

Periodic versus intermittent adaptive cycles in quasispecies coevolution

We study an abstract model for the coevolution between mutating viruses and the adaptive immune system. In sequence space, these two populations are localized around transiently dominant strains. Delocalization or error thresholds exhibit a novel interdependence because immune response is conditional on the viral attack. An evolutionary chase is induced by stochastic fluctuations and can occur via periodic or intermittent cycles. Using simulations and stochastic analysis, we show how the transition between these two dynamic regimes depends on mutation rate, immune response, and population size.

Adaptation of high-growth influenza H5N1 vaccine virus in Vero cells: implications for pandemic preparedness

Current egg-based influenza vaccine production technology can't promptly meet the global demand during an influenza pandemic as shown in the 2009 H1N1 pandemic. Moreover, its manufacturing capacity would be vulnerable during pandemics caused by highly pathogenic avian influenza viruses. Therefore, vaccine production using mammalian cell technology is becoming attractive. Current influenza H5N1 vaccine strain (NIBRG-14), a reassortant virus between A/Vietnam/1194/2004 (H5N1) virus and egg-adapted high-growth A/PR/8/1934 virus, could grow efficiently in eggs and MDCK cells but not Vero cells which is the most popular cell line for manufacturing human vaccines. After serial passages and plaque purifications of the NIBRG-14 vaccine virus in Vero cells, one high-growth virus strain (Vero-15) was generated and can grow over 10⁸ TCID₅₀/ml. In conclusion, one high-growth H5N1 vaccine virus was generated in Vero cells, which can be used to manufacture influenza H5N1 vaccines and prepare reassortant vaccine viruses for other influenza A subtypes.

[Evolution of adaptive immunity]

The current state of the problem of emergence and evolution of adaptive immunity in different taxonomic groups of animals is analyzed. Special attention is given to the emergence and phylogenetic development of the lymphocyte, the key component of immune response, as well as to the evolutionary development of T- and B-cell immune systems, adaptive immune responses and their molecular regulators (cytokines), and antigen-recognition structures.

Arrest of oogenesis in the bug Rhodnius prolixus challenged with the fungus Aspergillus niger is mediated by immune response-derived PGE2

In this work we characterized the immune response of the insect Rhodnius prolixus to a direct injection into the hemocoel of the non-entomopathogenic fungus Aspergillus niger, and evaluated its consequences on host oogenesis. These animals were able to respond by mounting effective cellular and humoral responses to this fungus; these responses were shown, however, to have reproductive fitness costs, as the number of eggs laid per female was significantly reduced. The disturbance of egg formation during infectious process correlated with an elevation in the titer of hemolymph prostaglandin E2 48 h post-challenge. Administration of Zymosan A as an immunogenic non-infectious challenge produced similar effects on phenoloxidase and prophenoloxidase activities, oocyte development and prostaglandin E2 titer, precluding the hypothesis of an effect mediated by fungal metabolites in animals challenged with fungus. Ovaries at 48 h post-challenge showed absence of vitellogenic ovarian follicles, and the in vivo administration of prostaglandin E2 or its receptor agonist misoprostol, partially reproduced this phenotype. Together these data led us to hypothesize that immune-derived prostaglandin E2 raised from the insect response to the fungal challenge is involved in disturbing follicle development, contributing to a reduction in host reproductive output and acting as a host-derived adaptive effector to infection.

Trogocytosis of MHC-I/peptide complexes derived from tumors and infected cells enhances dendritic cell cross-priming and promotes adaptive T cell responses

The transporter associated with antigen processing (TAP) and the major histocompatibility complex class I (MHC-I), two important components of the MHC-I antigen presentation pathway, are often deficient in tumor cells. The restoration of their expression has been shown to restore the antigenicity and immunogenicity of tumor cells. However, it is unclear whether TAP and MHC-I expression in tumor cells can affect the induction phase of the T cell response. To address this issue, we expressed viral antigens in tumors that are either deficient or proficient in TAP and MHC-I expression. The relative efficiency of direct immunization or immunization through cross-presentation in promoting adaptive T cell responses was compared. The results demonstrated that stimulation of animals with TAP and MHC-I proficient tumor cells generated antigen specific T cells with greater killing activities than those of TAP and MHC-I deficient tumor cells. This discrepancy was traced to differences in the ability of dendritic cells (DCs) to access and sample different antigen reservoirs in TAP and MHC-I proficient versus deficient cells and thereby stimulate adaptive immune responses through the process of cross-presentation. In addition, our data suggest that the increased activity of T cells is caused by the enhanced DC uptake and utilization of MHC-I/peptide complexes from the proficient cells as an additional source of processed antigen. Furthermore, we demonstrate that immune-escape and metastasis are promoted in the absence of this DC ‘arming’ mechanism. Physiologically, this novel form of DC antigen sampling resembles trogocytosis, and acts to enhance T cell priming and increase the efficacy of adaptive immune responses against tumors and infectious pathogens.

Immune response affects ant trophallactic behaviour

Sociality is associated with many benefits that have favoured its evolution in social insects. However, sociability also presents disadvantages like crowding of large numbers of individuals, which may favour the spread of infections within colonies. Adaptations allowing social insects to prevent and/or control pathogen infections range from behavioural responses to physiological ones including their immune systems. In a state of infection, social interactions with nestmates should be altered in a way which might prevent its spreading. We simulated a microbial infection in workers of the ant Camponotus fellah by the administration of peptidoglycan (PGN) and then quantified their immune response and social interactions. PGN injections as well as control injections of Ringer solution elicited similar production of antibacterial compounds, during 1-4 days after. However, injections of PGN reduced the ability of encapsulation of a nylon implant compared to Ringer controls. The immune challenged workers did not decrease the level of interactions with their nestmates. On the contrary, they devoted more time to trophallaxis. These results are discussed in relation to ant life history traits.

Habitat-specific adaptation of immune responses of stickleback (Gasterosteus aculeatus) lake and river ecotypes

Freshwater populations of three-spined sticklebacks (Gasterosteus aculeatus) in northern Germany are found as distinct lake and river ecotypes. Adaptation to habitat-specific parasites might influence immune capabilities of stickleback ecotypes. Here, naive laboratory-bred sticklebacks from lake and river populations were exposed reciprocally to parasite environments in a lake and a river habitat. Sticklebacks exposed to lake conditions were infected with higher numbers of parasite species when compared with the river. River sticklebacks in the lake had higher parasite loads than lake sticklebacks in the same habitat. Respiratory burst, granulocyte counts and lymphocyte proliferation of head kidney leucocytes were increased in river sticklebacks exposed to lake when compared with river conditions. Although river sticklebacks exposed to lake conditions showed elevated activation of their immune system, parasites could not be diminished as effectively as by lake sticklebacks in their native habitat. River sticklebacks seem to have reduced their immune-competence potential due to lower parasite diversity in rivers.

Clinal variation in MHC diversity with temperature: evidence for the role of host-pathogen interaction on local adaptation in Atlantic salmon

In vertebrates, variability at genes of the Major Histocompatibility Complex (MHC) represents an important adaptation for pathogen resistance, whereby high allelic diversity confers resistance to a greater number of pathogens. Pathogens can maintain diversifying selection pressure on their host's immune system that can vary in intensity based on pathogen richness, pathogen virulence, and length of the cohabitation period, which tend to increase with temperature. In this study, we tested the hypothesis that genetic diversity of MHC increases with temperature along a latitudinal gradient in response to pathogen selective pressure in the wild. A total of 1549 Atlantic salmon from 34 rivers were sampled between 46 degrees N and 58 degrees N in Eastern Canada. The results supported our working hypothesis. In contrast to the overall pattern observed at microsatellites, MHC class II allelic diversity increased with temperature, thus creating a latitudinal gradient. The observed temperature gradient was more pronounced for MHC amino acids of the peptide-binding region (PBR), a region that specifically binds to pathogens, than for the non-PBR. For the subset of rivers analyzed for bacterial diversity, MHC amino acid diversity of the PBR also increased significantly with bacterial diversity in each river. A comparison of the relative influence of temperature and bacterial diversity revealed that the latter could have a predominant role on MHC PBR variability. However, temperature was also identified as an important selective agent maintaining MHC diversity in the wild. Based on the bacteria results and given the putative role of temperature in shaping large-scale patterns of pathogen diversity and virulence, bacterial diversity is a plausible selection mechanism explaining the observed association between temperature and MHC variability. Therefore, we propose that genetic diversity at MHC class II represents local adaptation to cope with pathogen diversity in rivers associated with different thermal regimes. This study illuminates the link between selection pressure from the environment, host immune adaptation, and the large-scale genetic population structure for a nonmodel vertebrate in the wild.

Copolymer-1 induces adaptive immune anti-inflammatory glial and neuroprotective responses in a murine model of HIV-1 encephalitis

Copolymer-1 (COP-1) elicits neuroprotective activities in a wide range of neurodegenerative disorders. This occurs, in part, by adaptive immune-mediated suppression of microglial inflammatory responses. Because HIV infection and immune activation of perivascular macrophages and microglia drive a metabolic encephalopathy, we reasoned that COP-1 could be developed as an adjunctive therapy for disease. To test this, we developed a novel animal model system that reflects HIV-1 encephalitis in rodents with both innate and adaptive arms of the immune system. Bone marrow-derived macrophages were infected with HIV-1/vesicular stomatitis-pseudotyped virus and stereotactically injected into the basal ganglia of syngeneic mice. HIV-1 pseudotyped with vesicular stomatitis virus envelope-infected bone marrow-derived macrophages induced significant neuroinflammation, including astrogliosis and microglial activation with subsequent neuronal damage. Importantly, COP-1 immunization reduced astro- and microgliosis while diminishing neurodegeneration. Hippocampal neurogenesis was, in part, restored. This paralleled reductions in proinflammatory cytokines, including TNF-alpha and IL-1beta, and inducible NO synthase, and increases in brain-derived neurotrophic factor. Ingress of Foxp3- and IL-4-expressing lymphocytes into brains of COP-1-immunized animals was observed. We conclude that COP-1 may warrant therapeutic consideration for HIV-1-associated cognitive impairments.

Adaptive immune responses fail to provide protection against genital HSV-2 infection in the absence of IL-15

IL-15 plays a crucial role in innate defense against viral infections. The role of IL-15 in the generation and function of adaptive immunity, following mucosal immunization, against genital HSV-2 has not been studied. Here, we report that immunized IL-15(-/-) mice were able to generate antibody and T cell-mediated immune responses against HSV-2, comparable to those seen in immunized B6 mice. However, immunized IL-15(-/-) mice were not protected against subsequent HSV-2 challenge, compared to B6 immunized mice, even with a ten times lower challenge dose. We then examined if the adaptive immune responses generated in the absence of IL-15 could provide protection against HSV-2 in an IL-15-positive environment. Adoptive transfer of lymphocytes from immunized IL-15(-/-) to naive mice were able to provide protection against HSV-2 challenge similar to protection with immunized cells from control mice. This suggests that the adaptive immune responses raised in the absence of IL-15 are functional in vivo. Reconstitution of the innate components, particularly IL-15, NK cells and NK cell-derived IFN-gamma, in immunized IL-15(-/-) mice restored their protective adaptive immunity against subsequent genital HSV-2 challenge. Our results clearly suggest that innate antiviral activity of IL-15 is necessary for protective adaptive immunity against genital HSV-2 infection.

Fimbrial proteins of porphyromonas gingivalis mediate in vivo virulence and exploit TLR2 and complement receptor 3 to persist in macrophages

Porphyromonas gingivalis is an oral/systemic pathogen implicated in chronic conditions, although the mechanism(s) whereby it resists immune defenses and persists in the host is poorly understood. The virulence of this pathogen partially depends upon expression of fimbriae comprising polymerized fimbrillin (FimA) associated with quantitatively minor proteins (FimCDE). In this study, we show that isogenic mutants lacking FimCDE are dramatically less persistent and virulent in a mouse periodontitis model and express shorter fimbriae than the wild type. Strikingly, native fimbriae allowed P. gingivalis to exploit the TLR2/complement receptor 3 pathway for intracellular entry, inhibition of IL-12p70, and persistence in macrophages. This virulence mechanism also required FimCDE; indeed, mutant strains exhibited significantly reduced ability to inhibit IL-12p70, invade, and persist intracellularly, attributable to failure to interact with complement receptor 3, although not with TLR2. These results highlight a hitherto unknown mechanism of immune evasion by P. gingivalis that is surprisingly dependent upon minor constituents of its fimbriae, and support the concept that pathogens evolved to manipulate innate immunity for promoting adaptive fitness and thus their capacity to cause disease.

Patterns of nonclassical MHC antigen presentation

The identification of pattern-recognition receptors that selectively respond to evolutionarily conserved chemical (often pathogen-derived) moieties has provided key insight into how innate immune cells facilitate rapid and relatively specific antimicrobial immune activity. In contrast, relatively slower adaptive immune responses rely on T cell clonal expansion that develops in response to variable peptides bound to the groove of classical major histocompatibility complex (MHC) proteins. For certain nonclassical 'MHC-like' class Ib proteins, such as H2-M3 and CD1d, their respective binding grooves seem to have been adapted to present to T cells unique molecular patterns analogous to those involved in innate signaling. Here we propose that another MHC class Ib protein, MR1, which is required for the gut flora-dependent development of mucosa-associated invariant T cells, presents either a microbe-produced or a microbe-induced pattern.

Free Hemoglobin: A Dangerous Signal for the Immune System in Patients with Carotid Atherosclerosis?

Atherosclerosis is a chronic inflammatory multifactorial disease in which immune responses are key pathogenetic factors. T cell-mediated immunity contributes to the initiation and progression of atherosclerotic disease, but the nature of antigens responsible for immune cell activation is still not completely elucidated. Convincing evidence supports a determinant role of autoimmune responses to self-structures in shaping the progression of the disease. Autoimmune responses may be directed against altered self-structures, such as oxidized low-density lipoproteins (LDL). Oxidative stress, increasingly reported in patients with atherosclerosis, is the major event causing protein structural modification, thus inducing the appearance of neo/cryptic epitopes on the molecule. Intraplaque hemorrhage, a common event in advanced lesions, causes the deposition of large amounts of hemoglobin (Hb). The pro-oxidative intraplaque microenvironment may induce structural changes in extra-erythrocytic free Hb, thus generating novel/cryptic autoantigenic epitopes. We demonstrated that an oxidized Hb preparation enriched in hemichromes expands IFN-gamma-secreting T lymphocytes in patients with advanced carotid atherosclerosis and enhances the phenotypical and functional maturation of human monocyte-derived dendritic cells induced by lipopolysaccharide (LPS). Overall, our findings suggest that oxidized forms of Hb could act as a dangerous signal for the immune system, thus contributing to the inflammatory process that takes place within the atherosclerotic plaque.

Gamma-glutamyl transpeptidase has a role in the persistent colonization of the avian gut by Campylobacter jejuni

The contribution of gamma-glutamyl transpeptidase (GGT) to Campylobacter jejuni virulence and colonization of the avian gut has been investigated. The presence of the ggt gene in C. jejuni strains directly correlated with the expression of GGT activity as measured by cleavage and transfer of the gamma-glutamyl moiety. Inactivation of the monocistronic ggt gene in C. jejuni strain 81116 resulted in isogenic mutants with undetectable GGT activity; nevertheless, these mutants grew normally in vitro. However, the mutants had increased motility, a 5.4-fold higher invasion efficiency into INT407 cells in vitro and increased resistance to hydrogen peroxide stress. Moreover, the apoptosis-inducing activity of the ggt mutant was significantly lower than that of the parental strain. In vivo studies showed that, although GGT activity was not required for initial colonization of 1-day-old chicks, the enzyme was required for persistent colonization of the avian gut.

Distinct NKT cell subsets are induced by different Chlamydia species leading to differential adaptive immunity and host resistance to the infections

We investigated the role of NKT cells in immunity to Chlamydia pneumoniae and Chlamydia muridarum infections using a combination of knockout mice and specific cellular activation approaches. The NKT-deficient mice showed exacerbated susceptibility to C. pneumoniae infection, but more resistance to C. muridarum infection. Activation of NKT reduced C. pneumoniae in vivo growth, but enhanced C. muridarum infection. Cellular analysis of invariant NKT cells revealed distinct cytokine patterns following C. pneumoniae and C. muridarum infections, i.e., predominant IFN-gamma in the former, while predominant IL-4 in the latter. The cytokine patterns of CD4(+) and CD8(+) T cells matched those of NKT cells. Our data provide in vivo evidence for a functionally diverse role of NKT cells in immune response to two intracellular bacterial pathogens. These results suggest that distinct NKT subsets are induced by even biologically closely related pathogens, thus leading to differential adaptive immune response and infection outcomes.

The impact of T cell intrinsic antigen adaptation on peripheral immune tolerance

Overlapping roles have been ascribed for T cell anergy, clonal deletion, and regulation in the maintenance of peripheral immunological tolerance. A measurement of the individual and additive impacts of each of these processes on systemic tolerance is often lacking. In this report we have used adoptive transfer strategies to tease out the unique contribution of T cell intrinsic receptor calibration (adaptation) in the maintenance of tolerance to a systemic self-antigen. Adoptively transferred naïve T cells stably calibrated their responsiveness to a persistent self-antigen in both lymphopenic and T cell-replete hosts. In the former, this state was not accompanied by deletion or suppression, allowing us to examine the unique contribution of adaptation to systemic tolerance. Surprisingly, adapting T cells could chronically help antigen-expressing B cells, leading to polyclonal hypergammaglobulinemia and pathology, in the form of mild arthritis. The helper activity mediated by CD40L and cytokines was evident even if the B cells were introduced after extended adaptation of the T cells. In contrast, in the T cell-replete host, neither arthritis nor autoantibodies were induced. The containment of systemic pathology required host T cell-mediated extrinsic regulatory mechanisms to synergize with the cell intrinsic adaptation process. These extrinsic mechanisms prevented the effector differentiation of the autoreactive T cells and reduced their precursor frequency, in vivo.

Life and death in the granuloma: immunopathology of tuberculosis

During tuberculosis (TB) infection, the granuloma provides the microenvironment in which antigen-specific T cells colocate with and activate infected macrophages to inhibit the growth of Mycobacterium tuberculosis. Although the granuloma is the site for mycobacterial killing, virulent mycobacteria have developed a variety of mechanisms to resist this macrophage-mediated killing. These surviving mycobacteria become dormant, however, if host cellular immunity or the signals maintaining granuloma structure wane, or if mycobacteria resume replication, leading to reactivation of TB. This balance of life and death applies not only to the mycobacterium but also to the host macrophages that may undergo apoptosis or necrosis, leading to the characteristic caseous necrosis within the granuloma, and the potential spread of TB infection. The immunological factors controlling the development and maintenance of the granuloma will be reviewed.

Adaptation of humoral memory

Immunological memory, as provided by antibodies, depends on the continued presence of antibody-secreting cells, such as long-lived plasma cells of the bone marrow. Survival niches for these memory plasma cells are limited in number. In an established immune system, acquisition of new plasma cells, generated in response to recent pathogenic challenges, requires elimination of old memory plasma cells. Here, we review the adaptation of plasma cell memory to new pathogens. This adaptation is dependent upon the influx of plasmablasts, generated in a secondary systemic immune reaction, into the pool of memory plasma cells, the efficiency of competition of new plasmablasts with old plasma cells, and the frequency of infection with novel pathogens. To maintain old plasma cells at frequencies high enough to provide protection and to accommodate as many specificities as possible, an optimal influx rate per infection exists. This optimal rate is approximately three times higher than the minimal number of plasma cells providing protection. Influx rates of plasmablasts generated by vaccination approximately match this optimum level. Furthermore, the observed stability of serum concentrations of vaccine-specific antibodies implies that the influxing plasmablasts mobilize a similar number of plasma cells and that competitive infectious challenges are not more frequent than once per month.

From vanilla to 28 flavors: multiple varieties of T regulatory cells

Numerous T cell subpopulations have now been claimed to exhibit regulatory activity. Shevach discusses the current understanding of the different subsets of T regulatory cells and provides a perspective on the current areas of uncertainly and controversy in the field.

Alternative adaptive immunity in invertebrates

Vertebrate adaptive immunity is characterized by challenge-specific long-term protection. This specific memory is achieved through the vast diversity of somatically rearranged immunological receptors such as antibodies. Whether or not invertebrates are capable of a comparable phenotypic plasticity and memory has long been a matter of debate. A recent study on Anopheles gambiae mosquitoes now establishes Down syndrome cell adhesion molecule (Dscam) as a key immune surveillance factor with characteristics analogous to antibodies.

New insights to the immunopathology and autoimmune responses in primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is an autoimmune liver disease with profound changes in different compartments of the immune system, including those involved in innate, and adaptive immunity. New data from epidemiological studies of PBC have reinforced the thesis that the cause for this relatively uncommon disease is likely to be a combination of both environmental factors and a susceptible genetic predisposition. Recent findings of abnormalities of the innate immune system in PBC suggest that they may serve as links between the environmental factors and the early events in PBC development. Viral and bacterial infections as well as xenobiotics are some of the potential environmental factors that have been implicated in this complex process. Identification of the etiological factors for PBC will point to new preventive or therapeutic treatments.

Immunopathogenesis: role of innate and adaptive immune responses

Hepatitis B virus (HBV) infection in immunocompetent adults usually results in a self-limited, transient liver disease and viral clearance, with only a small percentage (5 to 10%) developing chronic hepatitis associated with viral persistence. In contrast, when neonates are infected, more than 90% become persistently infected, suffering differing degrees of chronic liver disease. Activation of immunity plays a central role in host-virus interactions, greatly influencing viral replication and the clinical outcome of infection. Although all of the specific mechanisms and consequences of this interaction have not been elucidated, the purpose of this article is to describe the basic arms of the immune system as they interact with the HBV and describe the present state of knowledge in this area. These arms may be divided broadly into innate and specific immune responses, and they have different roles and responses in acute and chronic infection.

The evolution of immune mechanisms

From early on in evolution, organisms have had to protect themselves from pathogens. Mechanisms for discriminating "self" from "non-self" evolved to accomplish this task, launching a long history of host-pathogen co-evolution. Evolution of mechanisms of immune defense has resulted in a variety of strategies. Even unicellular organisms have rich arsenals of mechanisms for protection, such as restriction endonucleases, antimicrobial peptides, and RNA interference. In multicellular organisms, specialized immune cells have evolved, capable of recognition, phagocytosis, and killing of foreign cells as well as removing their own cells changed by damage, senescence, infection, or cancer. Additional humoral factors, such as the complement cascade, have developed that co-operate with cellular immunity in fighting infection and maintaining homeostasis. Defensive mechanisms based on germline-encoded receptors constitute a system known as innate immunity. In jaw vertebrates, this system is supplemented with a second system, adaptive immunity, which in contrast to innate immunity is based on diversification of immune receptors and on immunological memory in each individual.Usually, each newly evolved defense mechanism did not replace the previous one, but supplemented it, resulting in a layered structure of the immune system. The immune system is not one system but rather a sophisticated network of various defensive mechanisms operating on different levels, ranging from mechanisms common for every cell in the body to specialized immune cells and responses at the level of the whole organism. Adaptive changes in pathogens have shaped the evolution of the immune system at all levels.

Differential activation of astrocytes by innate and adaptive immune stimuli

The immunologic privilege of the central nervous system (CNS) makes it crucial that CNS resident cells be capable of responding rapidly to infection. Astrocytes have been reported to express Toll-like receptors (TLRs), hallmark pattern recognition receptors of the innate immune system, and respond to their ligation with cytokine production. Astrocytes have also been reported to respond to cytokines of the adaptive immune system with the induction of antigen presentation functions. Here we have compared the ability of TLR stimuli and the adaptive immune cytokines interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha) to induce a variety of immunologic functions of astrocytes. We show that innate signals LPS- and poly I:C lead to stronger upregulation of TLRs and production of the cytokines IL-6 and TNF-alpha as well as innate immune effector molecules IFN-alpha4, IFN-beta, and iNOS compared with cytokine-stimulated astrocytes. Both innate stimulation and adaptive stimulation induce similar expression of the chemokines CCL2, CCL3, and CCL5, as well as similar enhancement of adhesion molecule ICAM-1 and VCAM-1 expression by astrocytes. Stimulation with adaptive immune cytokines, however, was unique in its ability to induce upregulation of MHC II and the functional ability of astrocytes to activate CD4(+) T cells. These results indicate potentially important and changing roles for astrocytes during the progression of CNS infection.

Major histocompatibility complex controls the trajectory but not host-specific adaptation during virulence evolution of the pathogenic fungus Cryptococcus neoformans

Genes of the major histocompatibility complex (MHC) play a critical role in immune recognition and are the most genetically diverse loci known. One hypothesis to explain this diversity postulates that pathogens adapt to common MHC haplotypes and thus favour selection of new or rare alleles. To determine whether the pathogenic yeast Cryptococcus neoformans adapts to MHC-dependent immune responses, it was serially passaged in two independent replicate lines of five B10 MHC-congenic strains and Balb/c mice. All passaged lines increased in virulence as measured by reduced host survival. MHC influenced the rate (trajectory) of virulence increase during passages as measured by significant differences in mortality rate (p < 0.001). However, when the post-passage strains were tested, no MHC differences in mortality rate remained and only minor differences in titres were observed. Also contrary to expectations, increased virulence in three lines passaged in B10 mice had a larger effect in Balb/c mice, and the evolution of virulence in lines passaged in alternating hosts was not retarded. To our knowledge, these data represent the first experimental test of MHC-specific adaptation in a non-viral pathogen. The failure to observe MHC effects despite dramatically increased virulence and host-genotype-specific adaptation to non-MHC genes suggests that escape of MHC-dependent immune recognition may be difficult for pathogens with unlimited epitopes or that other virulence factors can swamp MHC effects.

Adaptation of Campylobacter jejuni NCTC11168 to high-level colonization of the avian gastrointestinal tract

The genome sequence of the human pathogen Campylobacter jejuni NCTC11168 has been determined recently, but studies on colonization and persistence in chickens have been limited due to reports that this strain is a poor colonizer. Experimental colonization and persistence studies were carried out with C. jejuni NCTC11168 by using 2-week-old Light Sussex chickens possessing an acquired natural gut flora. After inoculation, NCTC11168 initially colonized the intestine poorly. However, after 5 weeks we observed adaptation to high-level colonization, which was maintained after in vitro passage. The adapted strain exhibited greatly increased motility. A second strain, C. jejuni 11168H, which had been selected under in vitro conditions for increased motility (A. V. Karlyshev, D. Linton, N. A. Gregson, and B. W. Wren, Microbiology 148:473-480, 2002), also showed high-level intestinal colonization. The levels of colonization were equivalent to those of six other strains, assessed under the same conditions. There were four mutations in C. jejuni 11168H that reduced colonization; maf5, flaA (motility and flagellation), and kpsM (capsule deficiency) eliminated colonization, whereas pglH (general glycosylation system deficient) reduced but did not eliminate colonization. This study showed that there was colonization of the avian intestinal tract by a Campylobacter strain having a known genome sequence, and it provides a model for colonization and persistence studies with specific mutations.

Gradual adaptation of HIV to human host populations: good or bad news?

The continuous evolution and adaptation of HIV to its host has produced extensive global viral diversity. Understanding the kinetics and directions of this continuing adaptation and its impact on viral fitness, immunogenicity and pathogenicity will be crucial to the successful design of effective HIV vaccines. Here we discuss some potential scenarios of viral and host coevolution.

Development of a "Type C" inventory: cross-cultural applications

The authors are preparing for cross-cultural studies of immunosuppressive behaviors and emotions, commonly called "Type C," in both healthy persons and in patients with cancer. To this end, validity and reliability of a Type C Personality Inventory were assessed in a sample of 128 healthy volunteers. Reliability of the instrument was supported by moderate to high Cronbach alpha coefficients. Acceptable validity was evident by relatively high correlations of the instrument's subscales with other, standardized, psychological tests.

Temperature-mediated processes in teleost immunity: in vitro immunosuppression induced by in vivo low temperature in channel catfish

In an attempt to understand the interrelationships between environmental temperature and immune competence, channel catfish in the laboratory were subjected to a rapid change in water temperature in order to mimic conditions which might be encountered in commercial ponds during the winter months and subsequently examined for a variety of immune parameters. The results indicated that lowering the water temperature from 23 to 11 degrees C over a 24 h period suppressed both B and T cell functions for 3-5 weeks as assessed by in vitro responses. Furthermore, this form of suppression was not a typical stress-induced response, i.e. blood serum chemistry and lymphocyte and neutrophil compositions did not change in a manner reminiscent of transport-induced stress. Collectively these results indicate that channel catfish are probably immunocompromised during the winter months and consequently it seems plausible that many of the fish losses associated with the syndrome termed "winter kill" may be attributable, at least in part, to a low temperature-induced immuno-deficient state.

Sexual reproduction as an adaptation to resist parasites (a review)

Darwinian theory has yet to explain adequately the fact of sex. If males provide little or no aid to offspring, a high (up to 2-fold) extra average fitness has to emerge as a property of a sexual parentage if sex is to be stable. The advantage must presumably come from recombination but has been hard to identify. It may well lie in the necessity to recombine defenses to defeat numerous parasites. A model demonstrating this works best for contesting hosts whose defense polymorphisms are constrained to low mutation rates. A review of the literature shows that the predictions of parasite coevolution fit well with the known ecology of sex. Moreover, parasite coevolution is superior to previous models of the evolution of sex by supporting the stability of sex under the following challenging conditions: very low fecundity, realistic patterns of genotype fitness and changing environment, and frequent mutation to parthenogenesis, even while sex pays the full 2-fold cost.

Loss of antibody productivity during long-term cultivation of a hybridoma cell line in low serum and serum-free media

A murine hybridoma cell line (167.4G5.3) was adapted to grow in different serum concentrations over a six month period of time. Adaptation to low serum and to serum-free media improved growth rates, but at low serum (1.25%) the antibody productivity was diminished. Flow cytometric analysis showed the presence of two distinct cell populations with respect to intracellular and surface antibody concentrations. The loss in antibody productivity during adaptation could be attributed to the appearance of a low antibody-containing cell population. Cultures maintained at high serum concentrations did not loose the original high antibody productivity. In a separate experiment the kinetics of growth improvement and loss of antibody production were studied for adaptation from 5% to 1.25% serum-containing media. Over a time period of about four months, the population shifted completely from high-producing cells to low-producing ones in response to the 1.25% environment. A shift-up from 1.25% to 20% serum resulted in the elimination of the low producing population. These results suggest that, for the cell line used, serum-containing factors prevent the loss of antibody productivity.