B cell mitogenic properties of thymus-independent antigens

Emerging vaccine strategies against the incessant pneumococcal disease

The incidence of invasive pneumococcal disease (IPD) caused by infection with the pathogen Streptococcus pneumoniae (Spn) has been on a downward trend for decades due to worldwide vaccination programs. Despite the clinical successes observed, the Center for Disease Control (CDC) reports that the continued global burden of S. pneumoniae will be in the millions each year, with a case-fatality rate hovering around 5%. Thus, it is a top priority to continue developing new Spn vaccination strategies to harness immunological insight and increase the magnitude of protection provided. As emphasized by the World Health Organization (WHO), it is also crucial to broaden the implementation of vaccines that are already obtainable in the clinical setting. This review focuses on the immune mechanisms triggered by existing pneumococcal vaccines and provides an overview of the current and upcoming clinical strategies being employed. We highlight the associated challenges of serotype selectivity and using pneumococcal-derived proteins as alternative vaccine antigens.

Development of a bivalent conjugate vaccine candidate against rotaviral diarrhea and tuberculosis using polysaccharide from Mycobacterium tuberculosis conjugated to ΔVP8* protein from rotavirus

Conjugation of carbohydrate antigens with a carrier protein is a clinically proven strategy to overcome the poor immunogenicity of bacterial polysaccharide. In addition to its primary role, which is to help generate a T cell-mediate long-lasting immune response directed against the carbohydrate antigen, the carrier protein in a glycoconjugate vaccine can also play an important role as a protective antigen. Among carrier proteins currently used in licensed conjugate vaccines, non-typeable Haemophilus influenzae protein D has been used as an antigenically active carrier protein. Our previous studies also indicate that some carrier proteins provide B cell epitopes, along with T cell helper epitopes. Herein we investigated the dual role of truncated rotavirus spike protein ΔVP8* as a carrier and a protective antigen. Capsular polysaccharide lipoarabinomannan (LAM), purified from Mycobacterium tuberculosis (M.tb), was chemically conjugated with ΔVP8*. Mouse immunization experiments showed that the resultant conjugates elicited strong and specific immune responses against the polysaccharide antigen, and the responses were comparable to those induced by Diphtheria toxoid (DT)-based conjugates. The conjugate vaccine induced enhanced antibody titers and functional antibodies against ΔVP8* when compared to immunization with the unconjugated ΔVP8*. Thus, these results indicate that ΔVP8* can be a relevant carrier protein for glycoconjugate vaccine and the glycoconjugates consisting of ΔVP8* with LAM are effective bivalent vaccine candidates against rotavirus and tuberculosis.

Influence of CD4-1+, CD4-2+ and CD8+ T lymphocytes subpopulations on the immune response of B lymphocytes in flounder (Paralichthys olivaceus) immunized with thymus-dependent or thymus-independent antigen

In order to elucidate the influence of T lymphocytes subpopulations on B lymphocytes immune response, in this paper, CD4-1⁺, CD4-2⁺, CD8⁺ T lymphocytes and B lymphocytes responses to thymus-independent (TI) or thymus-dependent (TD) antigen plus immunosuppressant were investigated in flounder (Paralichthys olivaceus). The results showed that in LPS-immunized group, the percentages of CD4-1⁺, CD4-2⁺, CD8β⁺ T (PCD4-1⁺ T, PCD4-2⁺ T and PCD8β⁺ T) lymphocytes in peripheral blood leucocytes (PBLs) had no significant variations, the percentages of IgM⁺ B (PIgM⁺ B) lymphocytes and LPS-specific antibodies (LA) significantly increased and peaked at 3^rd or 4^th week post-injection; CsA had no inhibition on both T/B lymphocytes and LA; RaPa only suppressed the PIgM⁺ B lymphocytes and LA, and the inhibition maximum (Imax) were about 35% and 20%, respectively. In KLH-immunized group, the PCD4-1⁺, PCD4-2⁺ and PCD8β⁺ T lymphocytes significantly increased and peaked at 3^rd or 5^th day, successively the PIgM⁺ B lymphocytes and KLH-specific antibodies (KA) significantly increased to the peak at 5^th week; the PCD4-1⁺, PCD4-2⁺ T and PIgM⁺ B lymphocytes and LA were inhibited significantly by both CsA and RaPa, and the Imax on them were 13%-33%, 11%-25%, 19%-34%, 22%-26%, respectively, while the PCD8β⁺ T lymphocytes showed no significant suppression. The results indicated that the suppression of PIgM⁺ B lymphocytes in KLH + CsA group was not directly derived from CsA, but due to the suppression of T lymphocytes, especially CD4⁺ T lymphocytes subpopulations. The results showed for the first time that, similar to higher vertebrates, T lymphocytes didn't respond to TI antigen, moreover, T lymphocyte subpopulations had a regulation on the immune response of B lymphocyte for TD antigen in flounder.

Outer membrane vesicles displaying engineered glycotopes elicit protective antibodies

The O-antigen polysaccharide (O-PS) component of lipopolysaccharides on the surface of gram-negative bacteria is both a virulence factor and a B-cell antigen. Antibodies elicited by O-PS often confer protection against infection; therefore, O-PS glycoconjugate vaccines have proven useful against a number of different pathogenic bacteria. However, conventional methods for natural extraction or chemical synthesis of O-PS are technically demanding, inefficient, and expensive. Here, we describe an alternative methodology for producing glycoconjugate vaccines whereby recombinant O-PS biosynthesis is coordinated with vesiculation in laboratory strains of Escherichia coli to yield glycosylated outer membrane vesicles (glycOMVs) decorated with pathogen-mimetic glycotopes. Using this approach, glycOMVs corresponding to eight different pathogenic bacteria were generated. For example, expression of a 17-kb O-PS gene cluster from the highly virulent Francisella tularensis subsp. tularensis (type A) strain Schu S4 in hypervesiculating E. coli cells yielded glycOMVs that displayed F. tularensis O-PS. Immunization of BALB/c mice with glycOMVs elicited significant titers of O-PS-specific serum IgG antibodies as well as vaginal and bronchoalveolar IgA antibodies. Importantly, glycOMVs significantly prolonged survival upon subsequent challenge with F. tularensis Schu S4 and provided complete protection against challenge with two different F. tularensis subsp. holarctica (type B) live vaccine strains, thereby demonstrating the vaccine potential of glycOMVs. Given the ease with which recombinant glycotopes can be expressed on OMVs, the strategy described here could be readily adapted for developing vaccines against many other bacterial pathogens.

Carbohydrates as T-cell antigens with implications in health and disease

Glycosylation is arguably the most ubiquitous post-translational modification on proteins in microbial and mammalian cells. During the past few years, there has been intensive research demonstrating that carbohydrates, either in pure forms or in conjunction with proteins or lipids, evoke and modulate adaptive immune responses. We now know that carbohydrates can be directly recognized by T cells or participate in T-cell stimulation as components of T-cell epitopes. T-cell recognition of carbohydrate antigens takes place via their presentation by major histocompatibility complex pathways on antigen-presenting cells. In this review, we summarize studies on carbohydrates as T-cell antigens modulating adaptive immune responses. Through discussion of glycan-containing antigens, such as glycoproteins, glycolipids, zwitterionic polysaccharides and carbohydrate-based glycoconjugate vaccines, we will illustrate the key molecular and cellular interactions between carbohydrate antigens and T cells and the implications of these interactions in health and disease.

Mouse Siglec-1 Mediates trans-Infection of Surface-bound Murine Leukemia Virus in a Sialic Acid N-Acyl Side Chain-dependent Manner

Siglec-1 (sialoadhesin, CD169) is a surface receptor on human cells that mediates trans-enhancement of HIV-1 infection through recognition of sialic acid moieties in virus membrane gangliosides. Here, we demonstrate that mouse Siglec-1, expressed on the surface of primary macrophages in an interferon-α-responsive manner, captures murine leukemia virus (MLV) particles and mediates their transfer to proliferating lymphocytes. The MLV infection of primary B-cells was markedly more efficient than that of primary T-cells. The major structural protein of MLV particles, Gag, frequently co-localized with Siglec-1, and trans-infection, primarily of surface-bound MLV particles, efficiently occurred. To explore the role of sialic acid for MLV trans-infection at a submolecular level, we analyzed the potential of six sialic acid precursor analogs to modulate the sialylated ganglioside-dependent interaction of MLV particles with Siglec-1. Biosynthetically engineered sialic acids were detected in both the glycolipid and glycoprotein fractions of MLV producer cells. MLV released from cells carrying N-acyl-modified sialic acids displayed strikingly different capacities for Siglec-1-mediated capture and trans-infection; N-butanoyl, N-isobutanoyl, N-glycolyl, or N-pentanoyl side chain modifications resulted in up to 92 and 80% reduction of virus particle capture and trans-infection, respectively, whereas N-propanoyl or N-cyclopropylcarbamyl side chains had no effect. In agreement with these functional analyses, molecular modeling indicated reduced binding affinities for non-functional N-acyl modifications. Thus, Siglec-1 is a key receptor for macrophage/lymphocyte trans-infection of surface-bound virions, and the N-acyl side chain of sialic acid is a critical determinant for the Siglec-1/MLV interaction.

History of interleukin-4

The history of the discovery and the development of our knowledge of IL-4 exemplifies the path of progress in biomedical science. There are unanticipated twists and turns although progress is made, sometimes quickly, other times far too slowly. Illustrative is the extended time from the first report of IL-4 in 1982 to the establishment of the efficacy of blocking IL-4 and its congener IL-13 in the treatment of moderate to severe asthma and atopic dermatitis, a period of 31years. The author was "present at the creation" and has been a participant or a witness to virtually all the major advances and recounts here his recollection of this history.

Pneumococcal vaccination: what have we learnt so far and what can we expect in the future?

Individuals <2 years and ≥ 50 years of age, as well as those with other specific risk factors, are especially vulnerable to invasive pneumococcal disease (IPD). Conjugate vaccines have been developed against encapsulated bacteria such as Streptococcus pneumoniae to provide improved immune responses. The 7-valent pneumococcal conjugate vaccine (PCV7) has significantly reduced the burden of vaccine-type pneumococcal diseases in children, including invasive disease and pneumonia and acute otitis media. There have also been significant declines in antimicrobial resistance in 7-valent vaccine serotypes and carriage of S. pneumoniae in the post-PCV7 era. Two to three years after the introduction of PCV13, there is emerging, global evidence of a reduced burden of pneumococcal diseases in children, including declines in IPD (UK and Germany) and nasopharyngeal carriage of PCV13 serotypes (Portugal and France). The functional immunogenicity of PCV13 in individuals ≥ 50 years of age has been demonstrated in clinical trials in comparison with the 23-valent pneumococcal polysaccharide vaccine and for children and adults 6 to 49 years of age. Between 2011 and 2013, PCV13 received market authorisation by the European Medicines Agency (EMA) for these additional age groups and is now available in Europe for the prevention of pneumococcal disease in all age groups.

Hijacking bacterial glycosylation for the production of glycoconjugates, from vaccines to humanised glycoproteins

OBJECTIVES

Glycosylation or the modification of a cellular component with a carbohydrate moiety has been demonstrated in all three domains of life as a basic post-translational process important in a range of biological processes. This review will focus on the latest studies attempting to exploit bacterial N-linked protein glycosylation for glycobiotechnological applications including glycoconjugate vaccine and humanised glycoprotein production. The challenges that remain for these approaches to reach full biotechnological maturity will be discussed.

KEY FINDINGS

Oligosaccharyltransferase-dependent N-linked glycosylation can be exploited to make glycoconjugate vaccines against bacterial pathogens. Few technical limitations remain, but it is likely that the technologies developed will soon be considered a cost-effective and flexible alternative to current chemical-based methods of vaccine production. Some highlights from current glycoconjugate vaccines developed using this in-vivo production system include a vaccine against Shigella dysenteriae O1 that has passed phase 1 clinical trials, a vaccine against the tier 1 pathogen Francisella tularensis that has shown efficacy in mice and a vaccine against Staphylococcus aureus serotypes 5 and 8. Generation of humanised glycoproteins within bacteria was considered impossible due to the distinct nature of glycan modification in eukaryotes and prokaryotes. We describe the method used to overcome this conundrum to allow engineering of a eukaryotic pentasaccharide core sugar modification within Escherichia coli. This core was assembled by combining the function of the initiating transferase WecA, several Alg genes from Saccharomyces cerevisiae and the oligosaccharyltransferase function of the Campylobacter jejuni PglB. Further exploitation of a cytoplasmic N-linked glycosylation system found in Actinobacillus pleuropneumoniae where the central enzyme is known as N-linking glycosyltransferase has overcome some of the limitations demonstrated by the oligosaccharyltransferase-dependent system.

SUMMARY

Characterisation of the first bacterial N-linked glycosylation system in the human enteropathogen Campylobacter jejuni has led to substantial biotechnological applications. Alternative methods for glycoconjugate vaccine production have been developed using this N-linked system. Vaccines against both Gram-negative and Gram-positive organisms have been developed, and efficacy testing has thus far demonstrated that the vaccines are safe and that robust immune responses are being detected. These are likely to complement and reduce the cost of current technologies thus opening new avenues for glycoconjugate vaccines. These new markets could potentially include glycoconjugate vaccines tailored specifically for animal vaccination, which has until today thought to be non-viable due to the cost of current in-vitro chemical conjugation methods. Utilisation of N-linked glycosylation to generate humanised glycoproteins is also close to becoming reality. This 'bottom up' assembly mechanism removes the heterogeneity seen in current humanised products. The majority of developments reported in this review exploit a single N-linked glycosylation system from Campylobacter jejuni; however, alternative N-linked glycosylation systems have been discovered which should help to overcome current technical limitations and perhaps more systems remain to be discovered. The likelihood is that further glycosylation systems exist and are waiting to be exploited.

On the origin of immunopathology

Stranded between medicine and experimental biology, immunology is buried in its own problems and remains distant from important areas of current biology, such as evolutionary theory, developmental biology and cognitive sciences. Immunology has treated the living system merely as the place or dimension in which immune activity takes place, inserted on a misleading axis (progressive responsiveness versus no response; memory versus tolerance) which neglects the analysis of a robustly stable dynamics which is always present and is neither tolerance nor immunity-a problem currently approached as one of "regulatory" activity. However, a regulatory response also demands regulation, leading to an endless recursion and the adoption of a stimulus-response framework inevitably drives us away from the physiological processes in which lymphocytes are involved. Herein, we propose that immunological physiology, like everything else in the body is dynamic and conservative. Immunopathology, including inherited immunodeficiencies, severe forms of infectious diseases, allergy and autoimmune diseases, are interferences with this stability which frequently include oligoclonal expansions of T lymphocytes. We suggest that this decrease in clonal diversity results from a loss of the stabilizing connectivity among lymphocytes and are not simply markers of immunopathology, but are rather expressions of basic pathogenic mechanisms. The so-called autoimmune diseases are examples of this disequilibrium. In the last decade the characterization of an enormous and diversified commensal microbiota has posed a new and pressing problem: how to explain the harmonic conviviality with trillions of foreign macromolecules. In addition, robustly stable relations towards macromolecular diet can be established by simple ingestion, a state presently labeled as "oral tolerance", a problem that has been buffered for decades as anti-inflammatory protection of the gut. A major change in terminology is necessary to describe this new panorama. We focus on two important gaps in immunological discussions: (a) the organism, seen simultaneously as the medium with which the immune system is constantly in touch and as the entity that mediates the contact with external materials; and (b) the observer, the immunologist, who operates as a human being in human languaging with other human beings, and characterizes immunological specificity. We acknowledge that we are proposing radical departures from current dogma and that we should justify them. Most of what we propose stem form a way of seeing called Biology of Cognition and Language, that derives from ideas of the neurobiologist/philosopher Humberto Maturana, also known as "autopoiesis theory".

Recent mechanistic insights on glycoconjugate vaccines and future perspectives

Vaccination is a key strategy for the control of various infectious diseases. Many pathogens, such as Streptococcus pneumoniae , Haemophilus influenzae type b (Hib), and Neisseria meningitidis produce on their surfaces dense and complex glycan structures, which represent an optimal target for eliciting carbohydrate specific antibodies able to confer protection against those bacteria. Glycoconjugates represent nowadays an important class of efficacious and safe commercial vaccines. It has been known for a long time that covalent linkage of poorly immunogenic carbohydrates to protein is fundamental to provide T cell epitopes for eliciting a memory response of the immune system against the saccharide. However, while the traditional mechanism of action of glycoconjugates has considered peptides generated from the carrier protein to be responsible of T cell help recruitment, only recently evidence of the active involvement of the carbohydrate part in determining the T cell help has been shown. In addition, zwitterionic polysaccharides have been proven to activate the adaptive immune system without further conjugation to protein. Progress in this interface area between chemistry and biology, in combination with novel synthetic and biosynthetic methods for the preparation of glycoconjugates, is opening new perspectives to clarify their mechanism of action and give new insights for the design of improved carbohydrate-based vaccines.

Carbohydrates and T cells: a sweet twosome

Carbohydrates as T cell-activating antigens have been generating significant interest. For many years, carbohydrates were thought of as T-independent antigens, however, more recent research had demonstrated that mono- or oligosaccharides glycosidically linked to peptides can be recognized by T cells. T cell recognition of these glycopeptides depends on the structure of both peptide and glycan portions of the antigen. Subsequently, it was discovered that natural killer T cells recognized glycolipids when presented by the antigen presenting molecule CD1d. A transformative insight into glycan-recognition by T cells occurred when zwitterionic polysaccharides were discovered to bind to and be presented by MHCII to CD4+ T cells. Based on this latter observation, the role that carbohydrate epitopes generated from glycoconjugate vaccines had in activating helper T cells was explored and it was found that these epitopes are presented to specific carbohydrate recognizing T cells through a unique mechanism. Here we review the key interactions between carbohydrate antigens and the adaptive immune system at the molecular, cellular and systems levels exploring the significant biological implications in health and disease.

Isolation of carbohydrate-specific CD4(+) T cell clones from mice after stimulation by two model glycoconjugate vaccines

Here we describe how to isolate carbohydrate-specific T cell clones (for which we propose the designation 'Tcarbs') after stimulation by two glycoconjugate vaccines. We describe how to prepare, purify and characterize two model glycoconjugate vaccines that can be used to generate Tcarbs. These glycoconjugate vaccines (GBSIII-OVA and GBSIII-TT) are synthesized by conjugation of type III group B streptococcal polysaccharide (GBSIII) to ovalbumin (OVA) or tetanus toxoid (TT). Upon immunization of mice with GBSIII-OVA, carbohydrate epitopes are presented to and recognized by CD4(+) T cells. Subsequently, polysaccharide-recognizing CD4(+) T cells are expanded in vitro by stimulating splenic CD4(+) T cells with GBSIII-TT. The sequential use of two distinct glycoconjugate vaccines containing the same polysaccharide conjugated to heterologous carrier proteins selects for and expands carbohydrate-specific T cells. This protocol can readily be adapted to study the stimulation of the immune system by alternative glycoconjugate vaccines. This protocol takes 1-2 years to complete.

A mechanism for glycoconjugate vaccine activation of the adaptive immune system and its implications for vaccine design

Although glycoconjugate vaccines have provided enormous health benefits globally, they have been less successful in significant high-risk populations. Exploring novel approaches to the enhancement of glycoconjugate effectiveness, we investigated molecular and cellular mechanisms governing the immune response to a prototypical glycoconjugate vaccine. In antigen-presenting cells, a carbohydrate epitope is generated upon endolysosomal processing of group B streptococcal type III polysaccharide coupled to a carrier protein. In conjunction with a carrier protein-derived peptide, this carbohydrate epitope binds to major histocompatibility class II (MHCII) and stimulates carbohydrate-specific CD4+ T-cell clones to produce interleukins 2 and 4—cytokines essential for providing T-cell help to antibody-producing B cells. An archetypical glycoconjugate vaccine constructed to maximize the presentation of carbohydrate epitopes recognized by T cells is 50–100 times more potent and significantly more protective in an animal model of infection than is a currently used vaccine construct.

How bacterial carbohydrates influence the adaptive immune system

The capsular polysaccharides (CPSs) of most pathogenic bacteria are T cell-independent antigens whose conjugation to carrier proteins evokes a carbohydrate-specific response eliciting T cell help. However, certain bacterial CPSs, known as zwitterionic polysaccharides (ZPSs), activate the adaptive immune system through processing by antigen-presenting cells and presentation by the major histocompatibility complex class II pathway to CD4(+) T cells. This discovery was the first mechanistic insight into how carbohydrates-a class of biological molecules previously thought to be T cell independent-can in fact activate T cells. Through their ability to activate CD4(+) T cells, ZPSs direct the cellular and physical maturation of the developing immune system. In this review, we explore the still-enigmatic relations between CPSs and the adaptive immune machinery at the cellular and molecular levels, and we discuss how new insights into the biological impact of ZPSs expand our concepts of the role of carbohydrates in microbial interactions with the adaptive immune system.

Type I Streptococcus pneumoniae carbohydrate utilizes a nitric oxide and MHC II-dependent pathway for antigen presentation

Some pathogenic bacteria form thick capsules that both block immune responses through inhibition of complement deposition and phagocytosis and stimulate a weak response resulting from a lack of T-cell involvement. Contrary to this model, capsular polysaccharides from 23 serotypes of Streptococcus pneumoniae have been successfully used in a multivalent vaccine in the absence of a carrier protein. Furthermore, type I pneumococcal polysaccharide (Sp1) has been shown to activate T cells in vivo and in vitro via an uncharacterized mechanism. In the present report, we demonstrate that Sp1 utilizes the major histocompatibility complex (MHC) class II pathway in antigen-presenting cells (APCs) for processing and presentation. APCs internalize and process Sp1 through a nitric oxide-dependent mechanism and, once inside the cell, it associates with MHC II proteins in an H-2M-dependent manner that leads to in vivo T-cell activation. These results establish that Sp1 activates T cells which can lead to abscess formation in mice through an H-2M-dependent polysaccharide antigen presentation pathway in APCs, potentially contributing to pneumococcal polysaccharide vaccine efficacy through the recruitment of T-cell help.

The love-hate relationship between bacterial polysaccharides and the host immune system

This article explores the fascinating relationship between the mammalian immune system and the bacteria that are present in the mammalian gut. Every human is an ecosystem that hosts 10(13)-10(14) bacteria. We review the evidence that immunomodulatory molecules produced by commensal bacteria in the gut have a beneficial influence on the development of certain immune responses, through eliciting the clonal expansion of CD4(+) T-cell populations. This process seems to contribute to the overall health of the host by offering protection against various diseases and might provide supporting evidence at a molecular level for the 'hygiene hypothesis' of allergic immune disorders.

Lipooligosaccharide of Campylobacter jejuni prevents myelin-specific enteral tolerance to autoimmune neuritis—a potential mechanism in Guillain-Barré syndrome?

Campylobacter jejuni-induced enteritis is the most common infection preceding Guillain-Barre syndrome (GBS), an immune-mediated polyradiculoneuritis. The acute autoimmune attack is thought to be based on C. jejuni antigens which may mimick antigens of the peripheral nervous system. Additional pathomechanisms, like disturbance of natural T cell immunoregulation by C. jejuni, have not been evaluated so far. In experimental autoimmune neuritis (EAN), a T lymphocyte-mediated animal model of human GBS, tolerance to myelin-derived autoantigens can be induced by oral feeding of the respective antigen. Here we investigated whether the lipooligosaccharide (LOS) fraction of C. jejuni may directly alter immunologic tolerance through gastrointestinal pathways. While EAN, actively induced by immunization with bovine peripheral nerve myelin could be ameliorated by precedent feeding of myelin, feeding of C. jejuni LOS along with the myelin antigen not only prevented the tolerizing effects of oral myelin but even accelerated the onset of overt EAN and augmented the myelin-specific B cell response. These findings provide evidence that LOS of C. jejuni, as produced in the gut during C. jejuni-induced enteritis, can disturb natural tolerance to definite proteins which may be or may mimic peripheral nerve antigens. In human patients this may be one of the potential mechanisms to explain why C. jejuni enteritis is a common trigger of GBS.

Roles of fructosyltransferase and levanase-sucrase of Actinomyces naeslundii in fructan and sucrose metabolism

The ability of Actinomyces naeslundii to convert sucrose to extracellular homopolymers of fructose and to catabolize these types of polymers is suspected to be a virulence trait that contributes to the initiation and progression of dental caries and periodontal diseases. Previously, we reported on the isolation and characterization of the gene, ftf, encoding the fructosyltransferase (FTF) of A. naeslundii WVU45. Allelic exchange mutagenesis was used to inactivate ftf, revealing that FTF-deficient stains were completely devoid of the capacity to produce levan-type (beta2,6-linked) polysaccharides. A polyclonal antibody was raised to a histidine-tagged, purified A. naeslundii FTF, and the antibody was used to localize the enzyme in the supernatant fluid. A sensitive technique was developed to detect levan formation by proteins that had been separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and the method was used to confirm that the levan-synthesizing activity of A. naeslundii existed predominantly in a cell-free form, that a small amount of the activity was cell associated, and that the ftf mutant was unable to produce levans. By using the nucleotide sequence of the levanase gene of a genospecies 2 A. naeslundii, formerly Actinomyces viscosus, a portion of a homologue of this gene (levJ) was amplified by PCR and inserted into a suicide vector, and the resulting construct was used to inactivate the levJ gene in the genospecies 1 strain WVU45. A variety of physiologic and biochemical studies were performed on the wild-type and LevJ-deficient strains to demonstrate that (i) this enzyme was the dominant levanase and sucrase of A. naeslundii; (ii) that LevJ was inducible by growth in sucrose; (iii) that the LevJ activity was found predominantly (>90%) in a cell-associated form; and (iv) that there was a second, fructose-inducible fructan hydrolase activity produced by these strains. The data provide the first detailed molecular analysis of fructan production and catabolism in this abundant and important oral bacterium.

Characterization of the fructosyltransferase gene of Actinomyces naeslundii WVU45

Oral actinomycetes produce fructosyltransferase (FTF) enzymes which convert sucrose into polymers of D-fructose, known as levans, and these polymers are thought to contribute to the persistence and virulence of the organisms. A gene encoding FTF was isolated from Actinomyces naeslundii WVU45; the deduced amino acid sequence showed significant similarity to known levansucrases of gram-negative environmental isolates but was less similar to FTFs from gram-positive bacteria. A transcriptional start site was mapped by primer extension 70 bp 5' from the putative start codon. Promoter fusions to a chloramphenicol acetyltransferase gene were used to confirm that there was a functional promoter driving ftf expression and to show that sequences located 86 to 218 bp upstream of the transcription initiation site were required for optimal ftf expression. Quantitative slot blot analysis against total RNA from cells grown on different sugars or from different growth phases revealed that ftf was constitutively transcribed. Thus, the A. naeslundii FTF is more similar in primary sequence and the regulation of expression to levansucrases of gram-negative bacteria than gram-positive bacteria.

Lymphocyte polyclonal activation: a pitfall for vaccine design against infectious agents

In this article, Bernardo Reina-San-Martin, Alain Cosson and Paola Minoprio summarize the marked alterations in the immune system functions after infection that might account for the poor success of effective parasite vaccine development. Many of the studies on oligoclonal B- and T-cell responses to parasite antigens aiming at vaccination strategies would seem to ignore more general, and perhaps fundamental, aspects of parasite-immune system interactions. In essence, because of its consequences on immunopathology and parasite escape, the authors ascribe a central importance in the pathogenesis of parasitic diseases to the 'nonspecific' polyclonal lymphocyte activation that occurs during infection. Hence, novel targets and strategies for immune intervention should be considered.

Receptors for innate pathogen defence in insects are normal activation receptors for specific immune responses in mammals

The Toll genes code for activation receptors for innate microbial defence in insects and have recently been found to code for the Lps receptor in murine B lymphocytes. In this study, I will present evidence to show that this family of receptors are responsible for induction of specific thymus-independent immune responses in mice. T cells do not possess these pattern-recognizing receptors, but they possess structures capable of delivering activation signals to these receptors on B cells.

Conditions for induction of specific and polyclonal antibody production by Cowan 1 bacteria and by pokeweed mitogen

Cowan 1 bacteria and pokeweed mitogen (PWM) were used to induce the formation of direct plaque-forming cells (PFC) against sheep erythrocytes (SRBC) by human peripheral blood lymphocytes in vitro. It was necessary to absorb the serum supplement with SRBC before culture to obtain anti-SRBC PFC. Alternatively, sheep serum could be added to the cultures. The PFC response was specific, and the response was equally high in cultures with a mixture of absorbed and non-absorbed serum as in cultures with absorbed serum only. Cowan 1 and PWM could also induce synthesis and secretion of both IgM and IgG polyclonal antibodies. Absorption with SRBC or addition of sheep serum had no effect on this synthesis. Thus it seems likely that the induction of anti-SRBC PFC by Cowan 1 or PWM needs the presence of SRBC antigen and is the result of a synergism between mitogen and antigen. Consequently, the anti-SRBC PFC response obtained after stimulation with Cowan 1 or PWM in SRBC-absorbed serum does not reflect a true polyclonal antibody response.

Growth of B cell colonies independent of T cells: a new perspective

Growth of human peripheral blood B cells in a B cell colony assay system is a useful technique to study the function of B cell biology. In the initial reports, T and B cells were admixed in the culture system, prior to which the T cells were treated with mitomycin or irradiation to prevent their proliferation. There were reports that optimal growth of B cell colonies required T cells to be in contact with the B cells. However, we were able to grow B cell colonies physically separated from T cells which were placed on a filter. We speculated then that T cells contacted B cells via pseudopods through the pores of the filter. We now report the growth of B cell colonies independent of T cells and conclude that B cell colony growth depends upon a critical number of B cells plated rather than on T cell help.

Stimulation by T cell independent antigens can relieve the arrest of differentiation of immature auto-reactive B cells in the bone marrow

The pair of microH-chain and kappa L-chain transgenes encoding the Sp6 TNP/DNA-specific IgM was bred onto the rearrangement-deficient genetic background of RAG-2T mice, and onto the kappa L-chain expression-deficient background of iE kappa T mice. Bone marrow of Sp6 transgenic RAG-2T mice contained normal numbers of B220(CD45R)+c-kit+ pro/preB-I-like cells and normal numbers of B220(CD45R)+TAC+ preB-II-like cells. Most strikingly, the numbers of immature sIgM+ B cells in the bone marrow were at least five-fold lower than normal, while mature B cells were almost undetectable in bone marrow as well as spleen. Hence, B cell development in these mice appears to be arrested at the transition from preB-II to immature B cells. The contents of bone marrow and spleen of the different precursors, immature and mature B cell compartments in Sp6iE kappa T mice were found to be similar to those of normal mice except that all sIg+ cells expressed lambda L-chains, of which 40% coexpressed the transgenic kappa L-chain. It indicates that the repertoire of lambda L-chain rearrangements and the lambda L-chains expressed from it suffices to relieve the arrest of differentiation seen in Sp6RAG-2T mice. The T cell-independent antigen TNP-Ficoll elicited within 5 days a response of the Sp6RAG-2T mice to develop to IgM-secreting cells and to fill the serum pool with the Sp6 transgenic IgM to 100 micrograms/ml, i.e. to normal serum levels of IgM in normal mice. TNP-Ficoll appears to interfere with the arrest of differentiation. Two scenarios for this arrest of differentiation and its relief by the T-independent antigen TNP-Ficoll are discussed.

Immunostimulatory potential of smokeless tobacco extract in in vitro cultures of murine lymphoid tissues

Despite numerous studies on the general toxicologic effects of smokeless tobacco (ST) little immunotoxicologic information is available. As a first step in assessing the potential activity of ST on the immune system, the effects of an aqueous extract of ST was studied in in vitro cultures of mouse lymphoid cells. There was a significant increase in the proliferation of spleen cells cultured with different concentrations of ST extract. The polyclonal IgM antibody responses as determined by protein A plaque assay were also elevated in ST stimulated spleen cell cultures. Similar immunostimulatory results were seen in the mesenteric lymph node cell cultures also. ST extract was able to stimulate the spleen cells of the immune defective CBA/N mice. The mitogenic ability of ST extract may not be due to lipopolysaccharide (LPS) contamination as determined by its response in the LPS resistant C3H/HeJ mice spleen cells. ST extract was mitogenic not only to B cells but also to T cells. However the magnitude of response was less in T cells than in B cells. The proliferation of T cells was not accompanied by secretion of IL-2 or expression of IL-2 receptors on T cells. However there was an increase of IL-1 activity in spleen cells cultured with ST extract. Finally, activation of B or T lymphocytes by ST did not result in the elevation of intracellular calcium levels. Since ST is consumed orally, the chronic immunostimulation by ST in oral mucosal lymphoid tissues may be associated with the increased incidence of gingivitis, leukoplakia and oral cancer seen in human ST users.

Effect of in vivo administration of the carcinogen benzo(a)pyrene on interleukin-2 and interleukin-3 production

B6C3F1 mice were exposed to the environmental carcinogen benzo(a)pyrene, a well known immunosuppressant. The ability of isolated splenocytes to produce and respond to the immunoregulatory molecules interleukin-2 (IL-2) and interleukin-3 (IL-3) was measured. Significant suppression by BaP of IL-2, but not IL-3, production following BaP exposure was observed. Further, exogenous recombinant IL-2 reconstituted the ability of splenocytes from benzo(a)pyrene treated mice to generate IgM antibody producing cells to the T-dependent antigens of sheep red blood cells. These results indicate that one of the cellular target(s) of BaP induced immunosuppression may be the mechanism(s) responsible for lymphokine production and regulation by activated T cells.

Slow cytotoxicity of the polysaccharide levan on tumor cells in vitro

Previous studies have shown that 1 h preincubation with levan caused a sharp decrease in tumorigenicity of tumor cells, although cell viability was not affected. In the present study, the possibility that levan might change the sensitivity of Lewis lung carcinoma cells to the host immune system and that levan might cause delayed damage were tested. Cell morphology, DNA synthesis, cell multiplication and viability as well as osmotic fragility were followed during several days in culture. Levan was found not to affect cell immunogenicity. The polysaccharide destroyed tumor cells by a rather peculiar mechanism: after a seemingly normal or even enhanced growth in culture during 3-5 days, cells suddenly burst. During the apparently normal growth, several morphological changes were observed: cell volume increased, cytoplasm swelled by apparent water uptake and some cells contained two or more nuclei. Levan-treated cells were found to be more susceptible to osmotic shock than non-treated cells. The reason for the sudden cell death could be a gradual increase in volume, up to a point which is no more compatible with membrane integrity, resulting in cell lysis.

Primary in vitro stimulation of antibody production by rainbow trout lymphocytes

Trinitrophenylated (TNP) forms of E. coli lipopolysaccharide (LPS) and keyhole limpet hemocyanin (KLH) were used to produce antigen specific plaque-forming cell (PFC) responses with rainbow trout (Salmo gairdneri) splenocytes from unprimed fish in vitro. The culture system that was developed is described and characterized with respect to the kinetics and dose responses for both the haptenated and unhaptenated forms of the carriers. The induction of the PFC response to TNP-LPS was inhibited with TNP-lysine. Exposure to graded levels of gamma-radiation demonstrated a low dose augmentation of the PFC response with both antigens. Antigen addition experiments reveal that both antigens appear to stimulate the same population of antibody-producing B lymphocytes.

Mycoplasma neurolyticum membranes: a T-independent antigen in the rat

Our understanding of the mechanisms involved in B cell activation, proliferation and differentiation to immunoglobulin secreting cells has been facilitated by the use of T-independent and T-dependent antigens. The majority of these studies have used the murine system and only recently, the rat. Because membranes isolated from Mycoplasma neurolyticum are potent B cell mitogens in the rat and some T-independent antigens also activate DNA synthesis in B cells, the in vitro and in vivo antibody responses induced by M. neurolyticum membranes in T-deficient rat systems were examined. The three groups of rats used, i.e., nude; anti-thymocyte serum-treated, neonatally-thymectomized (ATS-Tx); and normal Fischer 344 produced a non-polyclonal antibody response against the membranes. Spleen cell cultures that were T cell deficient and B cell enriched produced plaque-forming cells against the Mycoplasma membranes. Antibody production was depleted upon removal of Sephadex G-10 adherent cells. The antibody response is comprised of both antigen-specific and polyclonal responses. Lipoglycan, found in the aqueous phenol extract of the membranes, is the mitogenic fraction of the membranes, and this study suggests that it may also be the T-independent antigenic component of the M. neurolyticum membranes.

Modulation of interleukin-1 production by macrophages following benzo(a)pyrene exposure

The effects of benzo(a)pyrene (BaP), a highly prevalent environmental carcinogen, on the ability of peritoneal exudate macrophages to produce the secretory immunomodulatory molecule interleukin-1 (IL-1) in vitro was examined. A dose-dependent increase in lipopolysaccharide stimulated IL-1 production concomitant with decreased cell viabilities was noted in macrophages cultured in the presence of BaP. Antibody responses which are suppressed in BaP dosed mice can be reconstituted in vitro by the addition of exogenous interleukin-1. These results indicate that one of the cellular targets of BaP induced immunosuppression may be cells of the macrophage-monocyte lineage. Furthermore, BaP induced suppression of antibody responsiveness may be a result of alterations in production of IL-1.

Differential immunotoxic effects of the environmental chemical benzo[a]pyrene in young and aged mice

Young (3-6 months), middle-aged (16-18 months) and aged (23-26 months) mice were exposed in vitro and in vivo to the immunotoxic environmental chemical benzo[a]pyrene. The generation of antibody producing cells to the T-dependent antigens of sheep erythrocytes was observed to be suppressed in all age groups. Significantly, aged mice were shown to exhibit a greater percent suppression of antibody responses than young or middle-aged mice both in vitro and in vivo. The results presented provide the first evidence that the degree of immunological toxicity of environmental chemicals may be partially dependent upon the chronological and immunological age of the animal.

Antigen binding to lymphoid cells from unimmunized mice. VI. Specificity of purified multiple antigen-binding cells

In order to determine the specificity of antigen binding by double antigen-binding lymphocytes obtained from mouse bone marrow and spleen, three types of experiments were performed (1) a high excess of unlabelled antigen was tested for its ability to inhibit the binding of unrelated antigen to both single and double antigen-binding cells; (2) polyvalent anti-mouse immunoglobulin was assessed for its ability to inhibit antigen binding; and (3) the ability of one antigen to co-cap (or codistribute) with either another antigen or anti-immunoglobulin was studied to determine the spatial relationship of these components on the cell membrane. In order to study an adequate number of double ABC, these cells were enriched by using NIP-specific ABC as a starting population. The data indicate that double antigen binding occurs via independent immunoglobulin cell surface receptors which can be spatially separated from one another under appropriate capping conditions.

The polyclonal lipopolysaccharide response is accessory-cell-dependent

Different concentrations of spleen cells from C57BL.10 mice were activated with lipopolysaccharide (LPS), and DNA synthesis and IgM and IgG secretion were measured. The dilution curve was sigmoid, and the response was rapidly lost below a certain cell concentration. In the presence of thymocytes or spleen cells from the LPS-non-responder strain C57BL.10/ScCr the dilution curve for the LPS response of cells from C57BL.10 mice became linear, and the overall response was increased. Irradiated cells could not restore the response at suboptimal cell concentrations. In addition, enriched T cells restored the response as well as normal spleen cells, whereas enriched B cells did not. We compared the restoring capacity of different filler cells for the LPS response with that of a plasmacytoma cell line cultured at suboptimal cell concentrations. The results are compatible with the idea that the filler cells provide growth-stimulating activity to LPS-responsive cells but growth-supporting activity to the tumour cells. Furthermore, highly enriched B-cell populations respond poorly to LPS, but the response can be partly restored by filler cells. These data suggest that the LPS response is accessory-cell-dependent.

Effect of administration schedule on the levan-cyclophosphamide combined treatment of Lewis lung carcinoma

Combined treatment with levan and cyclophosphamide (CY) was applied intratumorally to Lewis lung carcinoma tumors in C57B1 mice on day 5 after tumor cell inoculation. Although on that day levan alone had no effect and CY alone caused only temporary regression of tumors, the combined CY-levan treatment caused 60% cure. Levan given before CY was almost as effective as simultaneous administration of both drugs on day 5. Delaying the administration of levan after CY treatment reduced the therapeutic effect. It is concluded that timing in relation to tumor cell inoculation as well as the order of administration of drugs, determine the degree of therapeutic efficacy. In tumor chemo-immunotherapy the final effect is probably due not only to the anti-tumoral effect per se of each drug, but also to the fact that the two agents have an effect on the immune system. Since the immune response may change during tumor development, the effect of timing of administration of an immunomodulator and certainly to two immunomodulators, can be crucial.

Regulatory function of Thy1-negative cells. I.--Evidence for cells without the Thy1-surface marker and without phagocytic properties, enhancing the IgM antibody response

Dextran-activated Thy1-cells are effective in enhancing the IgM anti-body response of syngeneic and allogeneic spleen cells to an unrelated antigen. This regulatory activity is mediated through a soluble B-cell-enhancing factor (BEF) which is released by activated cells. Removal of macrophages by silica-treatment does not abolish the regulatory activity of remaining cells. BEF can be considered as an auxiliary factor which does not substitute for either T cells or macrophages in in vitro antibody production.

Role of T cells in the mitogen-induced proliferation and polyclonal antibody response of murine B cells

The effect of thymus-derived lymphocytes (T cells) on the responsiveness of bone marrow-derived lymphocytes (B cells) to bacterial lipopolysaccharide (LPS) was determined in in vitro experiments. Radiation resistant splenic T cells obtained from euthymic nu/+ mice increased the number of proliferating cells in the cultures of splenic B cells from athymic nu/nu mice even in the nonstimulated state. The radiation resistant T cells augmented significantly the responsiveness of B cells to LPS, as determined by an increase in proliferating cells and polyclonally induced anti-sheep erythrocyte (SRBC) IgM hemolysin plaque-forming cells (PFC). Addition of the T cells to B cell cultures not only augmented the responsiveness of B cells to suboptimal doses of LPS but also enabled B cells to respond to supraoptimal doses of LPS. As is well documented, the radiation resistant T cells were unable to induce the generation of anti-SRBC PFC in B cell cultures, unless the cultures were simultaneously stimulated with SRBC. Colcemid, a specific inhibitor of cell mitosis, blocked almost completely the exponential generation of anti-SRBC PFC in B cell cultures responding to SRBC with the aid of radiation resistant T cells. In contrast, colcemid did not affect the exponential generation of anti-SRBC PFC of a polyclonal nature in B cell cultures responding to LPS, either in the presence or absence of radiation resistant T cells.

Polyclonal antibody production in murine spleen cells induced by Staphylococcus

Polyclonal plaque-forming cell (PFC) responses in murine spleen cells induced by Staphylococcus aureus and S. epidermidis were studied. Injection of Balb/c mice with S. aureus strain 248 beta H resulted in the generation of anti-trinitrophenyl (TNP) and anti-sheep red blood cell PFC in their spleens. Cultures of Balb/c mutant yielded many anti-TNP PFC. The larger the number of organisms that were added to the cultures, the better was the PFC response. Both living and killed organisms were capable of inducing the response, but an excess of living 248 beta H organisms in the cultures abrogated the response. All of the organisms (12 strains of S. aureus and 11 strains of S. epidermidis) freshly isolated from patients had the ability to induce the polyclonal PFC response in cell cultures. These organisms stimulated cultured C3H/HcJ mouse spleen cells, which were unresponsive to bacterial lipopolysaccharide (LPS). Cultured cells from the spleens of athymic mice also responded to these organisms, and the number of PFC in nu/nu cell cultures was always greater than in nu/+ cells prepared from a haired litter mate. Moreover, the responses of nu/nu spleen were lower than expected. These findings suggest that the polyclonal PFC response to staphylococci is thymus independent, but that the magnitude of the response is regulated by mature T cells. Cultures of macrophage-depleted spleen cells responded to the organisms to an extent similar to that of the control. The 248 beta H organisms were less capable of stimulating spleen cells of 2-week-old mice (i.e., early maturing B cells) than LPS. However, spleen cells from adult (7-week-old) and aged (9-month-old) mice responded well to both the organisms and LPS. Previous sensitization with the organisms in vivo did not affect any polyclonal responses of spleen cells in vitro to either the organisms or LPS. The role of staphylococcal protein A in the polyclonal PFC response to staphylococci is discussed.