Antigen-presenting cell types

Flt3 ligand augments immune responses to soluble PD1-based DNA vaccine via expansion of type 1 conventional DCs

DNA vaccines are prospective for their efficient manufacturing process, but their immunogenicity is limited as they cannot efficiently induce CD8+ T cell responses. A promising approach is to induce cross-presentation by targeting antigens to DCs. Flt3L can expand the number of type 1 conventional DCs and thereby improve cross-presentation. In this study, we first constructed a DNA vaccine expressing soluble PD1 and found that the therapeutic effect of targeting DCs with only the sPD1 vaccine was limited. When combined the vaccine with Flt3L, the anti-tumor effect was significantly enhanced. Considering the complexity of tumors and that a single method may not be able to activate a large number of effective CD8+ T cells, we combined different drugs and the vaccine with Flt3L based on the characteristics of different tumors. In 4T1 model, we reduced Tregs through cyclophosphamide. In Panc02 model, we increased activated DCs by using aCD40. Both strategies triggered strong CD8+ T cell responses and significantly improved the therapeutic effect. Our study provides important support for the clinical exploration of DC-targeted DNA vaccines in combination with Flt3L.

Rational design of ROS generation nanosystems to regulate innate immunity of macrophages, dendrtical and natural killing cells for immunotherapy

Innate immunity serves as the first line of host defense in the body against pathogenic infections or malignant diseases. Reactive oxygen species (ROS), as vital signaling mediators, can efficiently elicit innate immune responses to oxidative-related stress or damage. In the era of nanomedicine, various immunostimulatory nanosystems have been extensively designed and synthesized to elicit immune responses for the immunotherapy of cancer or infectious diseases. In this review, we emphasize that ROS derived from nanosystems regulates innate immune cells to potentiate immunotherapeutic efficacy, such as primarily dendritic cells, macrophages, or natural killer cells. Meanwhile, we also summarize the pathway of ROS generation triggered by exogenous nanosystems in innate immune cells of DCs, macrophages, and NK cells.

Immune cells in skin inflammation, wound healing, and skin cancer

Given the self-evident importance of cutaneous immunity in the maintenance of body-surface homeostasis, disturbance of the steady-state skin is inextricably intertwined with dysfunction in cutaneous immunity. It is often overlooked by people that skin, well-known as a solid physical barrier, is also a strong immunological barrier, considering the abundant presence of immune cells including lymphocytes, granulocytes, dendritic cells, and macrophages. What's more, humoral immune components including cytokines, immunoglobulins, and antimicrobial peptides are also rich in the skin. This review centers on skin inflammation (acute and chronic, infection and aseptic inflammation), wound healing, and skin cancer to elucidate the elaborate network of immune cells in skin diseases.

Fn-HMGB1 Adsorption Behavior Initiates Early Immune Recognition and Subsequent Osteoinduction of Biomaterials

Implantable biomaterials are widely used in bone tissue engineering, but little is still known about how they initiate early immune recognition and the initial dynamics. Herein, the early immune recognition and subsequent osteoinduction of biphasic calcium phosphate (BCP) after implantation to the protein adsorption behavior is attributed. By liquid chromatography tandem mass spectrometry (LC-MS/MS) analysis, the biomaterial-related molecular patterns (BAMPs) formed after BCP implantation are mapped, dominated by the highly expressed extracellular matrix protein fibronectin (Fn) and the high mobility group box 1 (HMGB1). Molecular dynamics simulations show that Fn has the ability to bind more readily to the BCP surface than HMGB1. The preferential binding of Fn provides a higher adsorption energy for HMGB1. Furthermore, multiple hydrogen bonding sites between HMGB1 and Fn are demonstrated using a molecular docking approach. Ultimately, the formation of BAMPs through HMGB1 antagonist glycyrrhizic acid (GA), resulting in impaired immune recognition of myeloid differentiation factor 88 (MYD88) mediated dendritic cells (DCs) and macrophages (Mφs), as well as failed osteoinduction processes is obstructed. This study introduces a mechanism for early immune recognition of implant materials based on protein adsorption, providing perspectives for future design and application of tissue engineering materials.

Immunotherapy of Cancer by Targeting Regulatory T cells

Regulatory T (Treg) cells maintain immune homeostasis by inhibiting abnormal/overactive immune responses to both autogenic and nonautogenic antigens. Treg cells play an important role in immune tolerance, autoimmune diseases, infectious diseases, organ transplantation, and tumor diseases. Treg cells have two functional characteristics: T cell anergy and immunosuppression. Treg cells remain immune unresponsive to high concentrations of interleukin-2 and anti-CD3 monoclonal antibodies. In addition, the activation of Treg cells after TCR-mediated signal stimulation inhibits the activation and proliferation of effector T cells. In the process of tumor development, Treg cells accumulate locally in the tumor and lead to tumor escape by inducing anergy and immunosuppression. It is believed that targeted elimination of Treg cells can activate tumor-specific effector T cells and improve the efficiency of cancer immunotherapy. Therefore, inhibition/clearance of Treg cells is a promising strategy for enhancing antitumor immunity. Here, we review studies of cancer immunotherapies targeting Treg cells.

Characterization and immunomodulatory activity of sulfated galactan from the red seaweed Gracilaria fisheri

Polysaccharides from the red seaweed Gracilaria fisheri possess many functions, which include antioxidant, antiviral, and antibacterial activities. However, detailed data on their immunomodulatory activities are scarce. Here, we isolated sulfated galactans (SG) from G. fisheri. We found that the predominant SG from G. fisheri, termed SG-1, had an estimated molecular mass of 100 kDa and activated murine J774A.1 macrophages via the dectin-1 signaling pathway. Furthermore, we observed enhancement of nitric oxide (NO) secretion, increased expression of inducible nitric oxide synthase (iNOS) mRNA, and increased mRNA levels of pro-inflammatory cytokines such as tumor necrosis factor-α (TNF-α) and interleukins IL-1β and IL-6 by SG-1 in macrophages. Moreover, there was higher expression of intercellular adhesion molecule 1 (ICAM-1) and co-stimulatory molecules (B7-1 and B7-2) mRNA. Treatment with G. fisheri SG-1 at 50 μg/mL generally achieved or exceeded the pro-inflammatory activities of 100 ng/mL lipopolysaccharide. Our study demonstrates immune-stimulatory activities of G. fisheri SG that may be of value for immune-potentiating treatment in humans or livestock.

A Review on Current COVID-19 Vaccines and Evaluation of Particulate Vaccine Delivery Systems

First detected in Wuhan, China, a highly contagious coronavirus, severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), also known as COVID-19, spread globally in December of 2019. As of 19 September 2021, approximately 4.5 million people have died globally, and 215 million active cases have been reported. To date, six vaccines have been developed and approved for human use. However, current production and supply capabilities are unable to meet global demands to immunize the entire world population. Only a few countries have been able to successfully vaccinate many of their residents. Therefore, an alternative vaccine that can be prepared in an easy and cost-effective manner is urgently needed. A vaccine that could be prepared in this manner, as well as can be preserved and transported at room temperature, would be of great benefit to public health. It is possible to develop such an alternative vaccine by using nano- or microparticle platforms. These platforms address most of the existing vaccine limitations as they are stable at room temperature, are inexpensive to produce and distribute, can be administered orally, and do not require cold chain storage for transportation or preservation. Particulate vaccines can be administered as either oral solutions or in sublingual or buccal film dosage forms. Besides improved patient compliance, the major advantage of oral, sublingual, and buccal routes of administration is that they can elicit mucosal immunity. Mucosal immunity, along with systemic immunity, can be a strong defense against SARS-CoV-2 as the virus enters the system through inhalation or saliva. This review discusses the possibility to produce a particulate COVID vaccine by using nano- or microparticles as platforms for oral administration or in sublingual or buccal film dosage forms in order to accelerate global vaccination.

Surface engineering for lymphocyte programming

The once nascent field of immunoengineering has recently blossomed to include approaches to deliver and present biomolecules to program diverse populations of lymphocytes to fight disease. Building upon improved understanding of the molecular and physical mechanics of lymphocyte activation, varied strategies for engineering surfaces to activate and deactivate T-Cells, B-Cells and natural killer cells are in preclinical and clinical development. Surfaces have been engineered at the molecular level in terms of the presence of specific biological factors, their arrangement on a surface, and their diffusivity to elicit specific lymphocyte fates. In addition, the physical and mechanical characteristics of the surface including shape, anisotropy, and rigidity of particles for lymphocyte activation have been fine-tuned. Utilizing these strategies, acellular systems have been engineered for the expansion of T-Cells and natural killer cells to clinically relevant levels for cancer therapies as well as engineered to program B-Cells to better combat infectious diseases.

Association between langerhans cells population and histological grade of oral squamous cell carcinoma

Context:

Langerhans cells (LCs) are a unique population of antigen processing cells in the epidermis and mucous membrane, which may play a role in the defence mechanism against epithelial tumors.

Aims:

To compare the distribution of LCs in oral squamous cell carcinomas (OSCC) and normal oral epithelium; and to determine whether the population of LCs in OSCC has any correlation with histological grading of these malignancies.

Settings and Design:

A cross-sectional immunohistochemical analysis of OSCC cases.

Materials and Methods:

Forty-eight randomly selected paraffin tissue blocks of OSCC cases and 30 cases of normal oral epithelium were included. Hematoxylin and eosin-stained sections of the OSCC cases were reviewed and categorized as high-grade malignant tumors or low-grade malignant tumors. Tissue sections were analyzed for density of LCs using CD1a antibody expression.

Statistical Analysis Used:

Data are expressed as percentages compared by Chi-square statistics; mean ± standard deviation, compared by Mann-Whitney-U test and Spearman's correlation tests.

Results:

LCs population was significantly higher in normal oral epithelium when compared with OSCC cases (P = 0.001). There was also a significant difference in the number of LCs per millimetre square area of tissue section between well-differentiated tumors and poorly-differentiated tumours (P = 0.03). There was a negative correlation between the population density of LCs and the grade of OSCC.

Conclusions:

These findings suggest that oral mucosal LCs are involved in immune-surveillance and immunologic impairment may characterize invasive OSCC. In addition, LCs density characterizes histological grades of OSCC, which may be of a prognostic value.

Micro and nanoparticle-based delivery systems for vaccine immunotherapy: an immunological and materials perspective

The development and widespread application of vaccines has been one of the most significant achievements of modern medicine. Vaccines have not only been instrumental in controlling and even eliminating life-threatening diseases like polio, measles, diphtheria, etc., but have also been immensely powerful in enhancing the worldwide outlook of public health over the past century. Despite these successes, there are still many complex disorders (e.g., cancer, HIV, and other emerging infectious diseases) for which effective preventative or therapeutic vaccines have been difficult to develop. This failure can be attributed primarily to our inability to precisely control and modulate the highly complex immune memory response, specifically the cellular response. Dominated by B and T cell maturation and function, the cellular response is primarily initiated by potent immunostimulators and antigens. Efficient and targeted delivery of these immunomodulatory and immunostimulatory molecules to appropriate cells is key to successful development of next generation vaccine formulations. Over the past decade, particulate carriers have emerged as an attractive means for enhancing the delivery efficacy and potency of vaccines and associated immunomodulatory molecules. Specifically, polymer-based micro and nanoparticles are being extensively studied for a wide variety of applications. In this review, we discuss the immunological fundamentals for developing effective vaccines and how materials and material properties can be exploited to improve these therapies. Particular emphasis is given to polymer-based particles and how the route of administration of particulate systems affects the phenotype and robustness of an immune response. Comparison of various strategies and recent advancements in the field are discussed along with insights into current limitations and future directions.

Effect of non-cell Corynebacterium Parvum on differentiation and maturation of bone marrow-derived dendritic cells

Corynebacterium parvum (CP), with their potent anti-tumor activities, has been well documented. Non-cell Corynebacterium Parvum (NCPP) is a neotype of biological preparation, which based on manipulating CP with nanotechnology. The present study was designed to investigate the effect of NCPP/CP on bone marrow derived dendritic cells (BMDCs) in tumor-bearing mice, especially focused on the differentiation and maturation of these BMDCs. BM cells from tumor-bearing mice administrated with NCPP/CP were analyzed by flow cytometry, which exhibit enhanced numbers of DCs and macrophages. In the meanwhile, flow cytometry analysis showed mild but significant difference for CD80 expression on these LPS- treated BMDCs between NCPP/CP administrated mice and the control animals. Furthermore, antigen presenting assay for these LPS-treated BMDCs showed significant difference for cytolytic assay of CD8+T cells against B16 melanoma cells, which indicate that NCPP treatments have enhanced the cytolytic rates of CD8+T cells from 47.9%±2.3% to 54.2%±2.4%. The data suggest that NCPP/CP treatment can efficiently facilitate the generation of BMDCs in vivo and enhance the maturation of these BMDCs in vitro.

Coinfection with nonlethal murine malaria parasites suppresses pathogenesis caused by Plasmodium berghei NK65

Mixed infection with different Plasmodium species is often observed in endemic areas, and the infection with benign malaria parasites such as Plasmodium vivax or P. malariae has been considered to reduce the risk of developing severe pathogenesis caused by P. falciparum. However, it is still unknown how disease severity is reduced in hosts during coinfection. In the present study, we investigated the influence of coinfection with nonlethal parasites, P. berghei XAT (Pb XAT) or P. yoelii 17X (Py 17X), on the outcome of P. berghei NK65 (Pb NK65) lethal infection, which caused high levels of parasitemia and severe pathogenesis in mice. We found that the simultaneous infection with nonlethal Pb XAT or Py 17X suppressed high levels of parasitemia, liver injury, and body weight loss caused by Pb NK65 infection, induced high levels of reticulocytemia, and subsequently prolonged survival of mice. In coinfected mice, the immune response, including the expansion of B220(int)CD11c(+) cells and CD4(+) T cells and expression of IL-10 mRNA, was comparable to that in nonlethal infection. Moreover, the suppression of liver injury and body weight loss by coinfection was reduced in IL-10(-/-) mice, suggesting that IL-10 plays a role for a reduction of severity by coinfection with nonlethal malaria parasites.

Destructive periodontitis lesions are determined by the nature of the lymphocytic response

It is now 35 years since Brandtzaeg and Kraus (1965) published their seminal work entitled "Autoimmunity and periodontal disease". Initially, this work led to the concept that destructive periodontitis was a localized hypersensitivity reaction involving immune complex formation within the tissues. In 1970, Ivanyi and Lehner highlighted a possible role for cell-mediated immunity, which stimulated a flurry of activity centered on the role of lymphokines such as osteoclast-activating factor (OAF), macrophage-activating factor (MAF), macrophage migration inhibition factor (MIF), and myriad others. In the late 1970s and early 1980s, attention focused on the role of polymorphonuclear neutrophils, and it was thought that periodontal destruction occurred as a series of acute exacerbations. As well, at this stage doubt was being cast on the concept that there was a neutrophil chemotactic defect in periodontitis patients. Once it was realized that neutrophils were primarily protective and that severe periodontal destruction occurred in the absence of these cells, attention swung back to the role of lymphocytes and in particular the regulatory role of T-cells. By this time in the early 1990s, while the roles of interleukin (IL)-1, prostaglandin (PG) E(2), and metalloproteinases as the destructive mediators in periodontal disease were largely understood, the control and regulation of these cytokines remained controversial. With the widespread acceptance of the Th1/Th2 paradigm, the regulatory role of T-cells became the main focus of attention. Two apparently conflicting theories have emerged. One is based on direct observations of human lesions, while the other is based on animal model experiments and the inability to demonstrate IL-4 mRNA in gingival extracts. As part of the "Controversy" series, this review is intended to stimulate debate and hence may appear in some places provocative. In this context, this review will present the case that destructive periodontitis is due to the nature of the lymphocytic infiltrate and is not due to periodic acute exacerbations, nor is it due to the so-called virulence factors of putative periodontal pathogens.

Generation of specific Th1 and CD8+ T-cell responses by immunization with mouse CD8+ dendritic cells loaded with HIV-1 viral lysate or envelope glycoproteins

Immunization with antigen-pulsed dendritic cells (DCs) can be used to elicit optimal immune responses. We developed the SRDC cell line, with a morphology, phenotype and activity similar to mouse splenic CD4(-)CD8alpha(+)CD205(+)CD11b(-) dendritic cells, which induce a polarized Th1 immune response. We evaluated the ability of SRDCs pulsed with HIV-1 viral lysate, oligomeric soluble gp140 or capsid p24 to induce specific antibody and T-cell responses in CBA/J mice. Immunization with all loaded SRDCs elicited antibody responses against the antigens tested. However, only HIV-1 viral lysate and gp140-pulsed SRDCs elicited specific CD4(+) and CD8(+) T-cell responses. These findings demonstrate the value of well characterized DC lines for optimizing the antigen-loading mixture, according to the DC population targeted. Our data suggest that splenic DCs pulsed with complex antigens, such as HIV-1 viral lysate or oligomeric soluble gp140, could be used as vaccines, eliciting strong primary Th1-polarized and humoral immune responses against HIV proteins in vivo.

Developing dendritic cells become 'lacy' cells packed with fat and glycogen

On maturation, dendritic cells (DCs) become highly active cells equipped for antigen uptake, migration and clustering and activation of T cells. We therefore asked whether DCs acquire fat and glycogen stores as they mature. DCs were generated from mouse bone marrow stem cells by culturing with granulocyte-macrophage colony-stimulating factor (GM-CSF) for 7-8 days. Stimulation of the DCs with lipopolysaccharide (LPS) for the last 24 hr of culture, or exposure to 1-15 ng/ml of interleukin (IL)-4 during development, resulted in production of DCs not only with an increased ability to stimulate T cells but also with an increasingly lacy appearance on transmission electron microscopy, with multiple unstained areas in the cytoplasm. This changed morphology was associated with the presence of increasing amounts of fat and glycogen, identified by Sudan Black and periodic acid leukofushin/Schiff (PAS) staining, respectively. Lacy DCs up-regulated type 1 and type 2 scavenger receptors, providing possible mechanisms contributing to these changes. Lacy DCs were found occasionally amongst freshly isolated splenic and lymph node DCs. DCs can be isolated from human adipose tissue, and we tested whether lacy DCs acquiring fat and glycogen were present in mouse omentum. CD45+ cells migrating from the omentum expressed specific DC markers CD11c and 33D1, costimulatory molecules and major histocompatibility complex (MHC) class II, and most showed darkly staining fat inclusions. Thus, during development, DCs can acquire large amounts of fat and glycogen, accumulation of which is promoted by antigen exposure and modulated by the cytokine milieu and location, and which may act as a link between energy stores and immune function.

Basic Concepts of Immune Response and Defense Development

The induction of immune responses requires critical interaction between innate parts of the immune system, which respond rapidly and in a relatively nonspecific manner, and other specific parts, which recognize particular epitopes on an antigen. A critical element in this interaction is the role played by dendritic cells (DCs), which represent "professional antigen-presenting cells." DCs endocytose and process antigen to peptide presented on the cell surface in association with major histocompatibility complex (MHC) molecules. This presentation results in interaction with and stimulation of helper T (Th) lymphocytes, which recognize peptide in association with either MHC class II or cytotoxic T (Tc) lymphocytes, which recognize peptide in association with MHC class I. Stimulation of Th lymphocytes produces the growth and differentiation factors (cytokines) essential for the B lymphocytes that have responded to a more intact form of the antigen and that differentiate into antibody-producing cells. The precise interaction between the cells depends on cognate ligand-receptor recognition between the B and Th lymphocytes. DCs also play a direct role with the stimulation of the B lymphocytes. It appears that DC can deliver antigen to the B lymphocytes in a more intact form than the processed form essential for stimulating T lymphocytes, and can release cytokines that assist the differentiation of the B lymphocytes into antibody-producing cells. This close relationship among the three cell types and the cytokines that are produced ensures the precise control and regulation necessary for immune response development.

Therapeutic dendritic-cell vaccine for chronic HIV-1 infection

We present the results of a preliminary investigation of the efficacy of a therapeutic dendritic cell (DC)-based vaccine for HIV-1. We immunized 18 chronically HIV-1-infected and currently untreated individuals showing stable viral loads for at least 6 months with autologous monocyte-derived DCs loaded with autologous aldrithiol-2-inactivated HIV-1. Plasma viral load levels were decreased by 80% (median) over the first 112 d following immunization. Prolonged suppression of viral load of more than 90% was seen in 8 individuals for at least 1 year. The suppression of viral load was positively correlated with HIV-1-specific interleukin-2 or interferon-gamma-expressing CD4(+) T cells and with HIV-1 gag-specific perforin-expressing CD8(+) effector cells, suggesting that a robust virus-specific CD4(+) T-helper type 1 (T(H)1) response is required for inducing and maintaining virus-specific CD8(+) effectors to contain HIV-1 in vivo. The results suggest that inactivated whole virus-pulsed DC vaccines could be a promising strategy for treating people with chronic HIV-1 infection.

IL-10-Producing B220+CD11c−APC in Mouse Spleen

APC acting at the early stages of an immune response can shape the nature of that response. Such APC will include dendritic cells (DCs) but may also include populations of B cells such as marginal zone B cells in the spleen. In this study, we analyze APC populations in mouse spleen and compare the phenotype and function of B220(+)CD11c(-) populations with those of CD11c(+) spleen DC subsets. Low-density B220(+) cells had morphology similar to DCs and, like DCs, they could stimulate naive T cells, and expressed high levels of MHC and costimulatory molecules. However, the majority of the B220(+) cells appeared to be of B cell lineage as demonstrated by coexpression of CD19 and surface Ig, and by their absence from RAG-2(-/-) mice. The phenotype of these DC-like B cells was consistent with that of B cells in the marginal zone of the spleen. On bacterial stimulation, they preferentially produced IL-10 in contrast to the DCs, which produced IL-12. Conventional B cells did not produce IL-10. The DC-like B cells could be induced to express low levels of the DC marker CD11c with maturational stimuli. A minority of the B220(+)CD11c(-) low-density cells did not express CD19 and surface Ig and may be a DC subset; this population also produced IL-10 on bacterial stimulation. B220(+) APC in mouse spleen that stimulate naive T cells and preferentially produce IL-10 may be involved in activating regulatory immune responses.

Advanced glycation end products modulate the maturation and function of peripheral blood dendritic cells

Advanced glycation end products (AGEs), a complex and heterogeneous group of posttranslational modifications of proteins in vivo, have been widely studied for their involvement in diabetic complications; these complications are largely vascular and accompanied by inflammation. Because dendritic cells (DCs) initiate and modulate inflammatory responses, we hypothesized that AGEs might exert immunomodulatory effects via antigen-presenting DCs. To test this hypothesis, we investigated effects of the AGE peptide, compared with the naked peptide, on maturation, costimulatory molecule expression, and function of DCs in peripheral blood. From flow cytometry, we found a dose-dependent inhibition in CD83 expression on DCs exposed for 2.5 h to each of two synthetic AGE peptides. A similar culture for 24 h additionally produced an inhibition of CD80 expression, whereas exposure to AGEs for 3 days induced a large increase in DC numbers and a concomitant loss of monocyte/macrophages. Exposure of DCs to AGEs resulted in a dose-dependent loss in their capacity to stimulate primary proliferation of allogeneic T-cells. We conclude that AGEs promote development of DCs but that these DCs fail to express maturation markers and lose the capacity to stimulate primary T-cell responses. Effects of AGEs on DCs could be instrumental in the immunological changes associated with diabetes.

New designs for cancer vaccine and artificial veto cells: an emerging palette of protein paints

Antigen-presenting cells (APC) can be refaced with "protein paints" that change the appearance of their T cell-oriented trans signal arrays. Our group has developed three categories of protein paints suitable for this kind of APC engineering: artificial glycosylphosphatidylinositol (GPI) proteins, palmitated-protein A:Fc*1 fusion protein conjugates, and trans signal converter proteins. Protein paints have been devised with either immune enhancement or suppression in mind. Costimulator * GPI and palmitated-protein A costimulator * Fcgamma1 conjugates can be used to augment the immune-activating potential of tumor cells. Alternatively, protein paints can be designed to transform APC into artificial veto cells, in essence creating Trojan horses capable of inhibiting pathogenic T cells. Trans signal converter proteins (TSCP) have been devised for this purpose. Our first paradigmatic inhibitory TSCP, CTLA-4 * Fas ligand, binds to APC, and in so doing, simultaneously blocks B7 costimulation (via CTLA-4) and sends inhibitory trans signals (via Fas ligand) to T cells with dramatic efficacy. Protein transfer offers a number of advantages over gene transfer in facilitating quantitative and combinatorial protein expression and simplifying in vivo applications; the palette of protein paints with immunotherapeutic potential will undoubtedly continue to evolve.

A complicated relationship: fulfilling the interactive needs of the T lymphocyte and the dendritic cell

T cells recognize antigenic peptides displayed on the surface of MHC-bearing antigen-presenting cells (APCs), and with sufficient costimulation become activated. However, the ability of an APC (even bearing the correct peptide) to initiate and fulfill the requirements for T cell activation is not easily achieved. Naive T cells use multiple copies of a single receptor to survey the vast array of peptides presented on an APC, and require multiple receptor engagements to initiate T cell activation. Dendritic cells (DCs) are specialized cells with optimal capabilities for priming naive CD4+ T cells. Activation occurs, after initial antigen recognition by T cells, followed by a rapid dialogue between the T cells and the DCs. The resulting changes in both the cytoskeleton and the expression or regulation of cell-surface molecules on both cell types act to further strengthen engagement. In this report, we review the fundamentals of CD4+ T helper cell : DC interactions and discuss recent data concerning the molecular characteristics of this engagement.

Gangliosides from human melanoma tumors impair dendritic cell differentiation from monocytes and induce their apoptosis

Gangliosides are ubiquitous membrane-associated glycosphingolipids, which are involved in cell growth and differentiation. Most tumor cells synthesize and shed large amounts of gangliosides into their microenvironment, and many studies have unraveled their immunosuppressive properties. In the present study we analyzed the effects of GM3 and GD3 gangliosides, purified from human melanoma tumors, on the differentiation of monocyte-derived dendritic cells (MoDC). At concentrations close to those detected in the sera from melanoma patients, both gangliosides dose-dependently inhibit the phenotypic and functional differentiation of MoDC, as assessed by a strong down-regulation of CD1a, CD54, CD80, and CD40 Ags and impaired allostimulatory function on day 6 of culture. Furthermore, GM3 and GD3 gangliosides decreased the viable cell yield and induced significant DC apoptosis. Finally, addition of GD3 to differentiating DC impaired their subsequent maturation induced by CD154. The resulting DC produced low amounts of IL-12 and large amounts of IL-10, a cytokine pattern that might hamper an efficient antitumor immune response. In conclusion, the results demonstrate that gangliosides impair the phenotypic and functional differentiation of MoDC and induce their apoptosis, which may be an additional mechanism of human melanoma escape.

Therapeutic dendritic-cell vaccine for simian AIDS

An effective immune response against human immunodeficiency virus or simian immunodeficiency virus (SIV) is critical in achieving control of viral replication. Here, we show in SIV-infected rhesus monkeys that an effective and durable SIV-specific cellular and humoral immunity is elicited by a vaccination with chemically inactivated SIV-pulsed dendritic cells. After three immunizations made at two-week intervals, the animals exhibited a 50-fold decrease of SIV DNA and a 1,000-fold decrease of SIV RNA in peripheral blood. Such reduced viral load levels were maintained over the remaining 34 weeks of the study. Molecular and cellular analyses of axillary and inguinal node lymphocytes of vaccinated monkeys revealed a correlation between decreased SIV DNA and RNA levels and increased SIV-specific T-cell responses. Neutralizing antibody responses were augmented and remained elevated. Inactivated whole virus-pulsed dendritic cell vaccines are promising means to control diseases caused by immuno- deficiency viruses.

Antigen-presenting cells in human periodontal disease tissues

T cells are present in the inflammatory infiltrates of periodontal disease lesions and require antigen presentation by antigen-presenting cells (APCs). While it is still not known whether Th1 or Th2 cells predominate in these lesions, it has been reported that different APCs may induce activation of different T-cell subsets. An immunoperoxidase technique was used to investigate the presence of CD1a+, CMRF-44+, CMRF-58+ and CD83+ dendritic cells, CD14+ macrophages or dendritic cell precursors and CD19+ B cells in gingival biopsies from 21 healthy or gingivitis and 25 periodontitis subjects. The samples were divided into three groups according to the size of infiltrate (group 1, small infiltrates; group 2, medium infiltrates; group 3, extensive infiltrates). The presence of numerous CD1a+ Langerhans cells was noted in the epithelium with no differences between the healthy/gingivitis and periodontitis groups. The percentage of CD83+ dendritic cells in the infiltrates was higher than the percentage of CD1a+, CMRF-44+ or CMRF-58+ dendritic cells. Endothelial cells positive for CD83 were found predominantly in areas adjacent to infiltrating cells, CD83+ dendritic cells being noted in the region of CD83+ endothelium. The percentage of CD14+ cells in the inflammatory infiltrates was similar to that of CD83+ dendritic cells. B cells were the predominant APC in group 2 and 3 tissues. The percentage of B cells in group 3 periodontitis lesions was increased in comparison with group 1 periodontitis tissues and also in comparison with group 3 healthy/gingivitis sections. Functional studies are required to determine the roles of different APC subpopulations in periodontal disease.

Microglia as liaisons between the immune and central nervous systems: functional implications for multiple sclerosis

Multiple sclerosis is a chronic demyelinating inflammatory disease of the central nervous system (CNS). As the tissue macrophage of the CNS, microglia have the potential to regulate and be regulated by cells of the CNS and by CNS-infiltrating immune cells. The exquisite sensitivity of microglia to these signals, coupled with their ability to develop a broad range of effector functions, allows the CNS to tailor microglial function for specific physiological needs. However, the great plasticity of microglial responses can also predispose these cells to amplify disproportionately the irrelevant or dysfunctional signals provided by either the CNS or immune systems. The consequences of such an event could be the conversion of self-limiting inflammatory responses into chronic neurodegeneration and may explain in part the heterogeneous nature of multiple sclerosis.

Dangerous liaisons: the role of "danger" signals in the immune response to gene therapy

Recent studies in gene transfer suggest that the innate immune system plays a significant role in impeding gene therapy. In this review, we examine factors that might influence the recruitment and activation of the innate system in the context of gene therapy. We have adopted a novel model of immunology that contends that the immune system distinguishes not between self and nonself, but between what is dangerous and what is not dangerous. In taking this perspective, we provide an alternative and complementary insight into some of the failures and successes of current gene therapy protocols.

Dendritic cells, antigen distribution and the initiation of primary immune responses to self and non-self antigens

Immunity or tolerance are determined through the bone marrow-derived, antigen-presenting cells, dendritic cells (DC). Stimulation of lymphocytes by different types of DC, DC at different stages of maturity and DC producing and responding to different growth factors modulate immune responses. Innate receptors for foreign or self antigens provide scope in DC for discrimination between different antigenic stimuli. DC also transfer processed antigens to other DC. We propose that DC do not stimulate responses to antigens in their own environment but only to antigens acquired from other DC, providing a mechanism for discriminating between environmental and non-environmental antigens.

Uncertainties - discrepancies in immunology

The many immunological observations and results from in-vitro or in-vivo experiments vary, and their interpretations differ enormously. A major problem is that within a normal distribution of biological phenomena, which are measurable with many methods, virtually anything is possible. Within a coevolutionary context, the definition of biologically relevant thresholds is an important key to improve our understanding of weaknesses and strengths of the immune system. This review is a personal view, comparing textbook rules and experiments using model antigens with observations on immunity against infections or tumors to critically evaluate our perception and understanding of specificity, affinity maturation, antigen presentation, selection of the class of the immune response, immunological memory and protective immunity, positive selection of T cells and self/nonself discrimination.

Critical role of B cells in the development of T cell tolerance to aeroallergens

Respiratory exposure to allergen induces the development of allergen-specific CD4(+) T cell tolerance that effectively protects against the development of allergic-sensitization and T(h)2-biased immunity. The establishment of T cell unresponsiveness to aeroallergens is an active process preceded by a transient phase of T cell activation that requires T cell co-stimulation and is critically influenced by the antigen-presenting cell type. In this study we examined the role of B cells in the development of respiratory tolerance following intranasal (i.n.) exposure to a prototypic protein antigen. We found that respiratory exposure of BCR-transgenic (Tg) mice to minute quantities of cognate antigen effectively induced T cell unresponsiveness, indicating that antigen presentation by antigen-specific B cells greatly enhanced the development of respiratory tolerance. In contrast, respiratory T cell unresponsiveness could not be induced in B cell-deficient JHD mice exposed to i.n. antigen, although T cell tolerance developed in JHD mice reconstituted with B cells, suggesting that B cells are required for the induction of respiratory T cell tolerance. Respiratory exposure of BCR-Tg mice to cognate antigen induced activation of antigen-specific T cells and partial activation of antigen-specific B cells, as demonstrated by enhanced expression by B cells of class II MHC and B7 molecules but lack of antibody secretion. Our data indicate that B cells critically influence the immune response to inhaled allergens and are required for the development of allergen-specific T cell unresponsiveness induced by respiratory allergen.

Leishmania major promastigotes inhibit dendritic cell motility in vitro

Using an in vitro transwell migration assay, we have demonstrated that products secreted by Leishmania major promastigotes inhibit the motility of dendritic cells (DC) by up to 93%. Inhibition was dose dependent and reversible. By inhibiting DC migration in vivo, L. major may therefore subvert DC from their potentially protective role during leishmaniasis.

Antigen presentation of Type II collagen in rats

Collagen-induced arthritis (CIA) is a T-cell dependent disease of rats which follows immunization with bovine type II collagen (bCII). Susceptibility to CIA is linked to the genes encoding the major histocompatibility complex (MHC), suggesting that antigen presentation is important in disease pathogenesis. Antigen-presenting cells (APC) (macrophages, dendritic cells (DC) and B cells) were prepared from WA/KIR/KCL rats and presentation of antigen, in the form of native protein (bCII) or synthetic peptide (bCII:184-198), was assessed in T-cell proliferation assays. Whilst macrophages inhibited proliferative responses to bCII, splenic or thymic low density cells, enriched for DC, presented both bCII and bCII(184-198) peptide. However, bone marrow-derived DC, which stimulated T-cell responses to OVA, failed to present bCII, suggesting differences in processing of these two antigens. B-cell depletion from lymph node cells abrogated the proliferative response to bCII and reconstitution of a T-cell population with B cells restored the proliferative response, indicating that B cells are important for stimulating T-cell responses to bCII. B cells play a critical role in CIA by producing pathogenic anti-bCII antibodies, and we propose that B cells are also important APC which present bCII to CD4+ T cells.

Immune modulation in cancer patients after adoptive transfer of anti-CD3/anti-CD28-costimulated T cells-phase I clinical trial

Anti-CD3/anti-CD28 monoclonal antibody-coactivated T cells (COACTs) proliferate, secrete tumoricidal cytokines, and mediate non-major histocompatibility complex (MHC)-restricted cytotoxicity. This phase I study was done to determine the safety, maximum tolerated dose, technical limits of expansion, and modulation of immune functions in cancer patients given COACTs. Coactivated T cells were produced by stimulating peripheral blood mononuclear cells (PBMCs) with OKT3 anti-CD3 and 9.3 (anti-CD28)-coated beads in the presence of 100 IU interleukin (IL)-2 per milliliter for 14 days. The beads were removed after 4 days of culture. Ten courses of COACTs were given to eight patients with renal cell (1), ovarian (2), breast (1), and colorectal (4) carcinomas; two patients received two courses of COACTs. Patients were given up to 10 x 10 9 COACTs twice a week for 3 weeks without dose-limiting toxicities. Patients at the first and second dose levels received a mean total of 17.6 and 42.4 x 10 9 COACTs, respectively. After 14 days of culture, the COACTs contained a mean of 57.5% CD4+ cells and 42.5% CD8+ cells, exhibited non-MHC-restricted cytotoxicity, and produced significant amounts of interferon (IFN)-gamma, tumor necrosis factor (TNF)-alpha, and granulocyte macrophage colony-stimulating factor (GM-CSF). Infusions were safe and induced measurable serum levels of IFNgamma, TNFalpha, and IL-4 in two patients. Peripheral blood mononuclear cells from patients who received COACTs secreted higher amounts of IFNgamma and GM-CSF on in vitro anti-CD3/anti-CD28 restimulation than PBMCs obtained before immunotherapy. The detection of cytokines in patient sera and enhanced in vitro production of cytokines by anti-CD3/anti-CD28-stimulated patient PBMCs after COACT infusions suggest that COACTs were modulating immune responses in cancer patients.

Defective surface expression of attractin on T cells in patients with common variable immunodeficiency (CVID)

The proliferative responses of T lymphocytes of a subset of patients with CVID are abnormally low. This may be due to abnormalities in extracellular interactions or signalling defects downstream from membrane-associated receptors. Demonstrating that the T cell receptor signalling was normal, we observed no abnormal pattern of activation-induced tyrosine phosphorylation in cells from CVID patients. Moreover, the addition of exogenous IL-2 increased the low proliferation to mitogens, thus indicating the integrity of the IL-2R signalling apparatus. Attractin is a rapidly expressed T cell activation antigen involved in forming an association between T cells and monocytes. Twenty-four to 48 h after activation by CD3 cross-linking, attractin expression was not up-regulated on the cells of CVID patients despite normal up-regulation of CD25 and CD26. On control cells, however, attractin expression was up-regulated together with CD25 and CD26. The addition of the purified 175-kD attractin was capable of restoring the proliferative response of peripheral blood mononuclear cells following CD3 X-L in the presence of suboptimal concentrations of rIL-2 (10 and 20 U/ml). The effect was dose-dependent with the maximal effect at a concentration of 500 ng/ml, and present at a concentration as low as 50 ng/ml. Due to the likely role of attractin in cell guidance and amplification of the immune response, our results indicate that the lack of up-regulation of the molecule in patients with CVID may in turn affect any further step of productive immune response. Our finding may also imply a potential therapeutic role for this novel molecule.

Flt3 ligand enhances the immunogenicity of a gag-based HIV-1 vaccine

Liposomes and Flt3 ligand (Flt3L), a ligand for the fms-like tyrosine kinase receptor Flt3/ FLK2, can augment the immune response to an HIV peptide vaccine. The HGP-30 peptide used in these studies is a synthetic peptide that corresponds to a highly conserved region of HIV-1 p17 gag (amino acids 86-115). Mice were immunized with HGP-30 or HGP-30 conjugated to keyhole limpet hemocyanin (KLH) and delayed-type hypersensitivity (DTH) responses, antibody (IgG) amount and antigen-specific proliferative responses by spleen cells were used to monitor the immune response. Daily injections of Flt3L prior to HGP-30 administration enhanced significantly an antigen-specific lymphocyte proliferation response when compared with Flt3L, HGP-30 alone or HGP-30 containing liposomes. Intravenous administration of HGP-30 was superior to intramuscular (i.m.) immunization for the induction of DTH responses. The HGP-30/KLH containing liposomes enhanced both DTH and antibody responses, while liposomes containing HGP-30 peptide elicited only T cell responses. In these studies, either Flt3L or liposomes increased DTH responses compared with the i.m. injection of the HGP-30 vaccine alone.

Dendritic cells in the rat pituitary gland evaluated by the use of monoclonal antibodies and electron microscopy

A detailed analysis of the difference in the localization and the immunoreactivity for various surface markers among folliculo-stellate cells, macrophages, and dendritic cells was performed using immunohistochemistry and electron microscopy of the rat pituitary gland. The folliculo-stellate cells were selectively labeled by an antiserum against S100 protein. The majority of dendritic cells were immunoreactive for the MHC class II (Ia) antigen (OX6) and/or the dendritic cell antibodies (OX62). The main population of macrophages was positive for the macrophage antibodies (ED1, ED2, and/or OX42). The cellular density of adenohypophyseal macrophages was significantly lower than that of folliculo-stellate cells and of dendritic cells. All the neurohypophyseal microglial cells were labeled with OX42, while the mAb OX6 labeled a small population of cells different from the cells identified by OX42 in the neurohypophysis. Double-immunoperoxidase staining for ED1 and OX6 revealed that positively stained cells could be classified into ED1+OX6-, ED1+OX6+, and ED1-OX6+ cells. Double staining with OX62 and OX6 mAbs showed that about 60% of the OX6+ cells were also immunolabeled with OX62 in the anterior lobe: OX62 detects a subpopulation of dendritic cells but does not recognize macrophage populations. Furthermore, double staining for S100 and OX6 resulted in no S100+ OX6+ cells. At the electron-microscopic level, reaction products for OX6 were confirmed in the cell membrane and labeled cells were distinguished from macrophages and folliculo-stellate cells by distinctive short, broad cytoplasmic processes and the rare presence of cytoplasmic organelles. Such cytological characteristics of the OX6-positive cells in the pituitary gland are similar to dendritic cells. Our results suggest that resident dendritic cells and folliculo-stellate cells are two different main components of interstitial cells in the pituitary gland.

Development of dendritic-cell based prostate cancer vaccine

Available treatments for metastatic prostate cancer have failed to demonstrate significant curative potential. Current efforts are now directed towards developments of novel strategies for the treatment of metastatic prostate cancer. Cancer immunotherapeutic strategies utilize patient immune system components to kill cancer cells. This review discusses progress in active specific immunotherapeutic approaches as potential alternative methods in the treatment of metastatic prostate cancer. One of the newest advances in cancer immunotherapy is the use of dendritic cells as the vehicle to deliver cancer antigens for an effective in vivo T cell activation. The development of dendritic cell-based prostate cancer vaccine, as well as results of several clinical trials in prostate cancer involving the administration of peptide-pulsed autologous dendritic cell pulsed are discussed.

Progress in active-specific immunotherapy of brain malignancies

Despite the significant advances in neurosurgical techniques and oncology treatment regimens, the prognosis of patients with brain malignancies remains dismal. Brain tumours remain as lethal in the beginning of this new millennium as they were 30 years ago. Among the promising treatment modalities being tested are various immunotherapeutic approaches. Development of cancer vaccines, also known as active-specific immunotherapy, for malignant brain tumours is summarised in this review. Understanding the mechanisms behind vaccinations and the initiation of immune response have helped the design and improvement of the efficacy of clinical vaccines. The emergence of the antigen-presenting properties of dendritic cells brings the cancer vaccine field into a new generation. Preclinical work on the use of dendritic cell-based vaccine for malignant brain tumours are encouraging. The move from these preliminary studies to the clinic is anticipated with high hope.

Increased activity of lymph node cells in experimental thermal injury: changes in accessory cells in injured area-draining lymph nodes

Accessory cell content and some of their functional characteristics were determined in regional lymph nodes which drain burn injury (DLN) in rats. Increase in percentages of non-specific esterase-positive cells and NBT+ macrophages and in numbers of dendritic cells were noted in cytospin preparations of draining lymph node cells (DLC) 24 and 72 h following thermal injury. An accumulation of B cells was also noted in the DLN paracortex region at these time points. Enrichment of ED1+ (rat macrophage marker) cells was noted in the adherent DLC population. Increased activity of interleukin-1 (IL-1) in conditioned medium from adherent DLC population and the increased stimulatory capacity of whole DLC or dendritic cell enriched-DLC fraction were noted in functional assays. Enrichment in accessory cells and an increase in their functional activity could contribute to the endogenous activity of regional lymph nodes which drain burned areas.

Dendritic cells enriched from swine thymus co-express CD1, CD2 and major histocompatibility complex class II and actively stimulate alloreactive T lymphocytes

Initial characterization and partial purification of thymic dendritic cells (DC) from miniature swine were carried out with the ultimate goal of using these cells to induce transplantation tolerance in this preclinical animal model. Immunohistochemical analysis of swine thymic tissue sections has shown DC to be large cells located in the medullary and the cortico-medullary regions as evidenced by the presence of surrounding Hassal bodies. These cells exhibit membrane processes and express the CD1, granulocyte/macrophage (G/M), and major histocompatibility complex (MHC) class II surface antigens, as well as the S100 cytosolic and nuclear markers found in humans to be specific for DC. Dendritic cells were purified from thymi following collagenase treatment, Percoll gradient centrifugation, and adhesion steps to plastic. Cells similar in morphology and phenotype to those described in tissue sections were detected in the lighter density layers of the gradient and represented 0.02% of the starting cell number. Removal of plastic nonadherent cells showed enrichment levels similar to those reported for murine and human DC. Two-colour flow cytometric analysis of purified pig DC identified these cells as MHC class IIhi, CD1+, CD2+, and G/M+. The dendritic nature of these cells was confirmed by their potent ability to stimulate alloreactive T lymphocytes. Modification of porcine thymic DC by transfer of allogeneic MHC genes and reinjection into the DC donor should permit testing of the role of this DC subset in the induction of transplantation tolerance.

Human decidua contains potent immunostimulatory CD83(+) dendritic cells

Dendritic cells (DCs) are sentinel cells of the immune system important in initiating antigen-specific T-cell responses to microbial and transplantation antigens. DCs are particularly found in surface tissues such as skin and mucosa, where the organism is threatened by infectious agents. The human decidua, despite its proposed immunosuppressive function, hosts a variety of immunocompetent CD45 cells such as natural killer cells, macrophages, and T cells. Here we describe the detection, isolation, and characterization of CD45(+), CD40(+), HLA-DR(++), and CD83(+) cells from human early pregnancy decidua with typical DC morphology. CD83(+) as well as CD1a(+) cells were found in close vicinity to endometrial glands, with preference to the basal layer of the decidua. In vitro, decidual CD83(+) cells could be enriched to approximately 30%, with the remainder of cells encompassing DC-bound CD3(+) T cells. Stimulation of allogeneic T cells in a mixed leukocyte reaction by the decidual cell fraction enriched for CD83(+) cells, was similar to that obtained with blood monocyte-derived DCs, demonstrating the potent immunostimulatory capacity of these cells. Decidual DCs with morphological, phenotypic, and functional characteristics of immunostimulatory DCs might be important mediators in the regulation of immunological balance between maternal and fetal tissue, leading to successful pregnancy.

Regulation of T cell cytokine production by dendritic cells

Previous work has established that the dendritic cells (DC) of mouse spleen regulate the IL-2 production, and hence the extent of proliferation, of the CD8 T cells they activate. It is now reported here that interaction of primary CD8 T cells with splenic CD8alpha- DC induced much higher production of IL-3, IFN-gamma and granulocyte-macrophage colony-stimulating factor (GM-CSF), as well as IL-2, than did interaction with CD8alpha+ splenic DC. Furthermore, the CD8alpha- DC also induced higher levels of IL-2, IL-3 and IL-10 production in primary CD4 T cells, compared with that induced by CD8alpha+ DC. These quantitative differences did not involve qualitative shifts in the type of cytokine produced. Interleukin-4 production remained low in all the primary T cell cultures and restimulation experiments in secondary cultures did not reveal any bias in the cytokine production profile. When exogenous IL-2 was added to the primary cultures to ensure equal proliferation in response to CD8alpha- or CD8alpha+ DC, the higher level of production of IL-3, IFN-gamma and GM-CSF induced by CD8alpha- DC was maintained. Thus, this general control of T cell cytokine production by splenic DC involves factors additional to those that govern activation of T cells into cell cycle.

Polyomavirus-infected dendritic cells induce antiviral CD8(+) T lymphocytes

CD8(+) T cells are critical for the clearance of acute polyomavirus infection and the prevention of polyomavirus-induced tumors, but the antigen-presenting cell(s) involved in generating polyomavirus-specific CD8(+) T cells have not been defined. We investigated whether dendritic cells and macrophages are permissive for polyomavirus infection and examined their potential for inducing antiviral CD8(+) T cells. Although dendritic cells and macrophages both supported productive polyomavirus infection, dendritic cells were markedly more efficient at presenting the immunodominant viral epitope to CD8(+) T cells. Additionally, infected dendritic cells, but not infected macrophages, primed anti-polyomavirus CD8(+) T cells in vivo. Treatment with Flt3 ligand, a hematopoietic growth factor that dramatically expands the number of dendritic cells, markedly enhanced the magnitude of virus-specific CD8(+) T-cell responses during acute infection and the pool of memory anti-polyomavirus CD8(+) T cells. These findings suggest that virus-infected dendritic cells induce polyomavirus-specific CD8(+) T cells in vivo and raise the potential for their use as cellular adjuvants to promote CD8(+) T cell surveillance against polyomavirus-induced tumors.

Monocyte-derived dendritic cells do not proliferate and are not susceptible to retroviral transduction

Dendritic cells may be generated ex vivo from CD34+ progenitor cells or peripheral blood mononuclear cells. Initial reports suggested that monocyte-derived dendritic cells (MoDCs) arise from a proliferating precursor and several groups subsequently reported successful retroviral transduction of these cells, again implying that cell division occurs. As this is of importance in the development of immunotherapy protocols, we investigated whether monocytes proliferate as they differentiate into MoDCs and also their susceptibility to retroviral transduction. During MoDC differentiation, there was a 51 +/- 12% reduction in cell number, 98% of cells were in G0/G1, no DNA synthesis was detectable and the cell cycle regulatory proteins pRb and p130 were in the hypophosphorylated forms observed in non-cycling cells. As expected from these results, MoDCs were refractory to transduction with a GALV1 pseudotyped Moloney murine leukaemia virus (MoMLV)-based retroviral vector. In contrast, generation of DCs from purified CD34 progenitors was accompanied by rapid entry into the cell cycle and a 41.1-fold cell expansion at the end of 14 d culture.