The absence of cutaneous lymph nodes results in a Th2 response and increased susceptibility to Leishmania major infection in mice

LTβR deficiency causes lymph node aplasia and impaired B cell differentiation

Secondary lymphoid organs (SLOs) provide the confined microenvironment required for stromal cells to interact with immune cells to initiate adaptive immune responses resulting in B cell differentiation. Here, we studied three patients from two families with functional hyposplenism, absence of tonsils, and complete lymph node aplasia, leading to recurrent bacterial and viral infections. We identified biallelic loss-of-function mutations in LTBR, encoding the lymphotoxin beta receptor (LTβR), primarily expressed on stromal cells. Patients with LTβR deficiency had hypogammaglobulinemia, diminished memory B cells, regulatory and follicular T helper cells, and dysregulated expression of several tumor necrosis factor family members. B cell differentiation in an ex vivo coculture system was intact, implying that the observed B cell defects were not intrinsic in nature and instead resulted from LTβR-dependent stromal cell interaction signaling critical for SLO formation. Collectively, we define a human inborn error of immunity caused primarily by a stromal defect affecting the development and function of SLOs.

Construction of lymph nodes-targeting tumor vaccines by using the principle of DNA base complementary pairing to enhance anti-tumor cellular immune response

Tumor vaccines, a crucial immunotherapy, have gained growing interest because of their unique capability to initiate precise anti-tumor immune responses and establish enduring immune memory. Injected tumor vaccines passively diffuse to the adjacent draining lymph nodes, where the residing antigen-presenting cells capture and present tumor antigens to T cells. This process represents the initial phase of the immune response to the tumor vaccines and constitutes a pivotal determinant of their effectiveness. Nevertheless, the granularity paradox, arising from the different requirements between the passive targeting delivery of tumor vaccines to lymph nodes and the uptake by antigen-presenting cells, diminishes the efficacy of lymph node-targeting tumor vaccines. This study addressed this challenge by employing a vaccine formulation with a tunable, controlled particle size. Manganese dioxide (MnO2) nanoparticles were synthesized, loaded with ovalbumin (OVA), and modified with A50 or T20 DNA single strands to obtain MnO2/OVA/A50 and MnO2/OVA/T20, respectively. Administering the vaccines sequentially, upon reaching the lymph nodes, the two vaccines converge and simultaneously aggregate into MnO2/OVA/A50-T20 particles through base pairing. This process enhances both vaccine uptake and antigen delivery. In vitro and in vivo studies demonstrated that, the combined vaccine, comprising MnO2/OVA/A50 and MnO2/OVA/T20, exhibited robust immunization effects and remarkable anti-tumor efficacy in the melanoma animal models. The strategy of controlling tumor vaccine size and consequently improving tumor antigen presentation efficiency and vaccine efficacy via the DNA base-pairing principle, provides novel concepts for the development of efficient tumor vaccines.

TLR-2 agonist Pam3CSK4 has no therapeutic effect on visceral leishmaniasis in BALB/c mice and may enhance the pathogenesis of the disease

Most of the existing Leishmania-related research about TLR-2 agonists was focusing on their role as adjuvants in the vaccine, few studied its therapeutic effect. This paper aims to explore the therapeutic effect of TLR-2 agonist Pam3CSK4 on Leishmania-infected mice and the underlying immune molecular mechanisms. In L. donovani-infected BALB/c mice, one group was treated with Pam3CSK4 after infection and the other group was not treated. Normal uninfected mice treated with Pam3CSK4 or untreated were used as controls. Parasite load, hepatic pathology and serum antibodies were detected to assess the severity of the infection. The expression of immune-related genes, spleen lymphocyte subsets and liver RNA-seq were employed to reveal possible molecular mechanisms. The results showed that the liver and spleen parasite load of infected mice in Pam3CSK4 treated and untreated groups had no statistical difference, indicating Pam3CSK4 might have no therapeutic effect on visceral leishmaniasis. Infected mice treated with Pam3CSK4 possessed more hepatic inflammation focus, lower IgG and IgG2a antibody titers, and a lower proportion of spleen CD3+CD4+ T cells. Transcriptome analysis revealed that Th1/Th2 differentiation, NK cells, Th17 cell, complement system and calcium signaling pathways were down-regulated post-treatment of Pam3CSK4. In this study, TLR-2 agonist Pam3CSK4 showed no therapeutic effect on visceral leishmaniasis in BALB/c mice and might enhance the pathogenesis of the disease possibly due to the down-regulation of several immune-related pathways, which can improve our understanding of the role of TLR-2 in both treatment and vaccine development.

Immune Responses in Leishmaniases: An Overview

Leishmaniasis is a parasitic, widespread, and neglected disease that affects more than 90 countries in the world. More than 20 Leishmania species cause different forms of leishmaniasis that range in severity from cutaneous lesions to systemic infection. The diversity of leishmaniasis forms is due to the species of parasite, vector, environmental and social factors, genetic background, nutritional status, as well as immunocompetence of the host. Here, we discuss the role of the immune system, its molecules, and responses in the establishment, development, and outcome of Leishmaniasis, focusing on innate immune cells and Leishmania major interactions.

Nanotechnology-Based Approaches to Promote Lymph Node Targeted Delivery of Cancer Vaccines

Vaccines are a promising immunotherapy that awakens the human immune system to inhibit and eliminate cancer with fewer side effects compared with traditional radiotherapy and chemotherapy. Although cancer vaccines have shown some efficacy, there are still troublesome bottlenecks to expand their benefits in the clinic, including weak immune effects and limited therapeutic outcomes. In the past few years, in addition to neoantigen screening, a main branch of the efforts has been devoted to promoting the lymph nodes (LNs) targeting of cancer vaccines and the cross-presentation of antigens by dendritic cells (DCs), two cardinal stages in effective initiation of the immune response. Especially, nanomaterials have shown hopeful biomedical applications in the improvement of vaccine effectiveness. This Review briefly outlines the possible mechanisms by which nanoparticle properties affect LN targeting and antigen cross-presentation and then gives an overview of state-of-the-art advances in improving these biological outcomes with nanotechnology.

Role of host genetics and cytokines in Leishmania infection

Cytokines and chemokines are important regulators of innate and specific responses in leishmaniasis, a disease that currently affects 12 million people. We overviewed the current information about influences of genetically engineered mouse models of cytokine and chemokine on leishmaniasis. We found that genetic background of the host, parasite species and sub-strain, as well as experimental design often modify effects of genetically engineered cytokine genes. Next we analyzed genes and QTLs (quantitative trait loci) that control response to Leishmania species in mouse in order to establish relationship between genetic control of cytokine expression and organ pathology. These studies revealed a network-like complexity of the combined effects of the multiple functionally diverse QTLs and their individual specificity. Genetic control of organ pathology and systemic immune response overlap only partially. Some QTLs control both organ pathology and systemic immune response, but the effects of genes and loci with the strongest impact on disease are cytokine-independent, whereas several loci modify cytokines levels in serum without influencing organ pathology. Understanding this genetic control might be important in development of vaccines designed to stimulate certain cytokine spectrum.

Aryl Hydrocarbon Receptor-Signaling Regulates Early Leishmania major-Induced Cytokine Expression

The early inflammatory skin micromilieu affects resistance in experimental infection with Leishmania major. We pursue the concept that macrophages, which take up parasites during early infection, exert decisive influence on the inflammatory micromilieu after infection. In order to analyze their distinctive potential, we identified differentially regulated genes of murine granuloma macrophages (GMΦ) from resistant and susceptible mice after their infection with metacyclic Leishmania major. We found induction of several cytokines in GMΦ from both strains and a stronger upregulation of the transcription factor aryl hydrocarbon receptor (AhR) in GMΦ from resistant mice. Using both an AhR agonist and antagonist we demonstrated that AhR is involved in Leishmania-induced production of TNF in macrophages. In vivo, single local injection of an AhR agonist in early lesions of susceptible mice caused an increased induction of Tnf and other cytokines in the skin. Importantly, local agonist treatment led to a reduction of disease severity, reduced parasite loads and a weaker Th2 response. Our results demonstrate that local activation of AhR has a beneficial effect in experimental leishmaniasis.

T cell-derived lymphotoxin limits Th1 response during HSV-1 infection

Though lymphotoxin (LT) is highly expressed by type I helper T (Th1) cells, its contribution to CD4+ T cell differentiation during infections and diseases remains a mystery. In HSV-1 infection, we observed that LTβR signaling is required to limit the Th1 response. Using bone marrow chimeric mice, mixed-T-cell chimeric mice, and LTβR in vivo blockades, we unexpectedly observed that LT, especially T cell-derived LT, played an indispensable role in limiting the Th1 response. The LTβR-Ig blockade promoted the Th1 response by increasing infiltration of monocytes and monocyte-derived DCs and up-regulating IL-12 secretion in the lymphoid environment. Our findings identified a novel role for T cell-derived LT in manipulating Th1 differentiation.

The Lymphotoxin β Receptor Is Essential for Upregulation of IFN-Induced Guanylate-Binding Proteins and Survival after Toxoplasma gondii Infection

Lymphotoxin β receptor (LTβR) signaling plays an important role in efficient initiation of host responses to a variety of pathogens, encompassing viruses, bacteria, and protozoans via induction of the type I interferon response. The present study reveals that after Toxoplasma gondii infection, LTβR^−/− mice show a substantially reduced survival rate when compared to wild-type mice. LTβR^−/− mice exhibit an increased parasite load and a more pronounced organ pathology. Also, a delayed increase of serum IL-12p40 and a failure of the protective IFNγ response in LTβR^−/− mice were observed. Serum NO levels in LTβR^−/− animals rose later and were markedly decreased compared to wild-type animals. At the transcriptional level, LTβR^−/− animals exhibited a deregulated expression profile of several cytokines known to play a role in activation of innate immunity in T. gondii infection. Importantly, expression of the IFNγ-regulated murine guanylate-binding protein (mGBP) genes was virtually absent in the lungs of LTβR^−/− mice. This demonstrates clearly that the LTβR is essential for the induction of a type II IFN-mediated immune response against T. gondii. The pronounced inability to effectively upregulate host defense effector molecules such as GBPs explains the high mortality rates of LTβR^−/− animals after T. gondii infection.

Transcription of Toll-Like Receptors 2, 3, 4 and 9, FoxP3 and Th17 Cytokines in a Susceptible Experimental Model of Canine Leishmania infantum Infection

Canine leishmaniosis (CanL) due to Leishmania infantum is a chronic zoonotic systemic disease resulting from complex interactions between protozoa and the canine immune system. Toll-like receptors (TLRs) are essential components of the innate immune system and facilitate the early detection of many infections. However, the role of TLRs in CanL remains unknown and information describing TLR transcription during infection is extremely scarce. The aim of this research project was to investigate the impact of L. infantum infection on canine TLR transcription using a susceptible model. The objectives of this study were to evaluate transcription of TLRs 2, 3, 4 and 9 by means of quantitative reverse transcription polymerase chain reaction (qRT-PCR) in skin, spleen, lymph node and liver in the presence or absence of experimental L. infantum infection in Beagle dogs. These findings were compared with clinical and serological data, parasite densities in infected tissues and transcription of IL-17, IL-22 and FoxP3 in different tissues in non-infected dogs (n = 10), and at six months (n = 24) and 15 months (n = 7) post infection. Results revealed significant down regulation of transcription with disease progression in lymph node samples for TLR3, TLR4, TLR9, IL-17, IL-22 and FoxP3. In spleen samples, significant down regulation of transcription was seen in TLR4 and IL-22 when both infected groups were compared with controls. In liver samples, down regulation of transcription was evident with disease progression for IL-22. In the skin, upregulation was seen only for TLR9 and FoxP3 in the early stages of infection. Subtle changes or down regulation in TLR transcription, Th17 cytokines and FoxP3 are indicative of the silent establishment of infection that Leishmania is renowned for. These observations provide new insights about TLR transcription, Th17 cytokines and Foxp3 in the liver, spleen, lymph node and skin in CanL and highlight possible markers of disease susceptibility in this model.

Association of prevalence of rhinitis, atopic eczema, rhinoconjunctivitis and wheezing with mortality from infectious diseases and with antibiotic susceptibility at a country level

BACKGROUND

It was previously reported that there is a positive correlation between incidence of type 1 diabetes and prevalence of asthma and atopic eczema. A negative correlation between the prevalence of type 1 diabetes and mortality from infectious diseases as well as a positive correlation with antibiotic susceptibility at a country level have also been reported.

OBJECTIVE

The aim of this study was to investigate the association between country prevalence of rhinitis, atopic eczema, rhinoconjunctivitis, and wheezing with mortality from infectious diseases and also with antibiotic susceptibility at a country level.

METHODS

Data for prevalence of rhinitis, eczema, rhinoconjunctivitis, and wheezing was obtained from the International Study of Asthma and Allergies in Childhood study (ISAAC). ISAAC Phase one was a multicentre multicountry cross sectional study involving over 700,000 children in 2 age groups of school children, 13-14 years old (adolescents) and 6-7 years old (children) in 156 centres from 56 countries. Mortality from infectious diseases was taken from World Health Organisation data. The Alexander project was used to identify antibiotic susceptibilities to common bacteria.

RESULTS

There were significant positive correlations between atopic eczema and mortality from all infectious diseases studied, diarrhoeal illness, tropical infections, and childhood infections. A negative correlation exists between the prevalence of rhinitis and Streptococcus pneumoniae susceptibility to penicillin and to erythromycin, rhinitis and Haemophilus influenzae susceptibility to ampicillin and between rhinoconjunctivitis and H. influenzae susceptibility to ampicillin.

CONCLUSION

Th1/Th2 responses might influence the pathogenesis of infectious disease mortality, while antibiotic overprescription could explain the negative association between atopy and antibiotic susceptibility.

Linking the microbiota and metabolic disease with lymphotoxin

The field of lymphotoxin biology has seen many advances in the past decade. Notably, a role for lymphotoxin as a key effector cytokine has emerged to add to its foundational contribution to lymphoid organogenesis. It is now clear that lymphotoxin contributes to host defense for a wide variety of pathogens, and the lymphotoxin receptor is a defining feature of and regulatory mechanism in both innate and adaptive immunities. Specifically, lymphotoxin contributes to Th education, licensing of IL-22 production from type 3 innate lymphoid cells, and even maintains innate myeloid populations within the fully developed lymph node. Most recently, lymphotoxin has been implicated in regulation of the microbiota and metabolic disease. Early studies revealed that lymphotoxin might influence composition of the commensal microbiota through its regulation of immunological compartmentalization in the gut. Additionally, several epidemiological studies have linked polymorphisms in lymphotoxin to metabolic disease. Studies exploring the role of lymphotoxin in metabolic disease have demonstrated that lymphotoxin may influence metabolism both directly in the liver and indirectly through regulation of gut immune responses. It now appears that lymphotoxin may bridge the gap between altered composition of the commensal microbiota and metabolism.

Lymphotoxin signalling in immune homeostasis and the control of microorganisms

Lymphotoxin (LT) is a member of the tumour necrosis factor (TNF) superfamily that was originally thought to be functionally redundant to TNF, but these proteins were later found to have independent roles in driving lymphoid organogenesis. More recently, LT-mediated signalling has been shown to actively contribute to effector immune responses. LT regulates dendritic cell and CD4(+) T cell homeostasis in the steady state and determines the functions of these cells during pathogenic challenges. The LT receptor pathway is essential for controlling pathogens and even contributes to the regulation of the intestinal microbiota, with recent data suggesting that LT-induced changes in the microbiota promote metabolic disease. In this Review, we discuss these newly defined roles for LT, with a particular focus on how the LT receptor pathway regulates innate and adaptive immune responses to microorganisms.

Lymph node hypertrophy following Leishmania major infection is dependent on TLR9

Control of the protozoan parasite Leishmania major is dependent on establishing a robust T cell response. An early event in the development of an effective T cell response is the expansion (or hypertrophy) of the lymph node draining the site of infection, although the mechanisms involved in this response are not completely understood. In this study, we show that lymph node hypertrophy following L. major infection in mice is associated with increased recruitment of lymphocytes to the lymph node from the blood, and that CD62L-deficient mice, which are unable to recruit cells to the lymph node, develop a chronic infection with L. major. Injection of L. major-activated dendritic cells promoted lymph node hypertrophy, and this correlated with an increase in the expression of CCR7 on dendritic cells, although the upregulation of CCR7 occurred on the bystander (uninfected) dendritic cells rather than those containing parasites. We found that increased CCR7 expression was TLR9-dependent, that TLR9(-/-) dendritic cells migrated less efficiently to the draining lymph node, and that TLR9(-/-) mice exhibited a deficit in lymph node expansion following L. major infection, as well as increased susceptibility. Taken together, to our knowledge, these results are the first to demonstrate that activation of dendritic cells via TLR9 is essential for the induction of lymph node hypertrophy in leishmaniasis.

Cell biology and immunology of Leishmania

More than 20 years ago, immunologists discovered that resistance and susceptibility to experimental infection with the intracellular protozoan Leishmania major was associated with the development of T-helper 1 (Th1)- and Th2-dominated immune responses, respectively. This infectious disease model was later used to identify and assess the role of key factors, such as interleukin-12 (IL-12) and IL-4, in Th1 and Th2 maturation. While infection by Leishmania remains a popular model for immunologists who wish to assess the role of their favorite molecule in T-cell differentiation, other investigators have tried to better understand how Leishmania interact with its insect and mammalian hosts. In this review, we discuss some of these new data with an emphasis on the early events that shape the immune response to Leishmania and on the immune evasion mechanisms that allow this parasite to avoid the development of sterilizing immunity and to secure its transmission to a new host.

Role of the gut-associated and secondary lymphoid tissue in the induction of chronic colitis

BACKGROUND

It is well known that enteric bacterial antigens drive the development of chronic colitis in a variety of different mouse models of the inflammatory bowel diseases (IBD). The objective of this study was to evaluate the role of gut-associated lymphoid tissue (GALT; Peyer's patches, isolated lymphoid follicles), mesenteric lymph nodes (MLNs) and spleen in the pathogenesis of chronic colitis in mice.

METHODS

Surgical as well as genetic approaches were used to generate lymphopenic mice devoid of one or more of these lymphoid tissues. For the first series of studies, we subjected recombinase activating gene-1-deficient mice (RAG(-/-) ) to sham surgery (Sham), mesenteric lymphadenectomy (MLNx), splenectomy (Splx) or both (MLNx/Splx). In a second series of studies we intercrossed lymphotoxinβ-deficient (LTβ(-/-) ) mice with RAG(-/-) animals to generate LTβ(-/-) x RAG(-/-) offspring that were anticipated to contain functional MLNs but be devoid of GALT and most peripheral lymph nodes. Flow purified naïve (CD4(+) CD45RB(high) ) T-cells were adoptively transferred into the different groups of RAG(-/-) recipients to induce chronic colitis.

RESULTS

We found that at 3-5 wks following T-cell transfer, all four of the surgically-manipulated RAG(-/-) groups (Sham, MLNx, Splx and MLNx/Splx) developed chronic colitis that was similar in onset and severity. Flow cytometric analysis revealed no differences among the different groups with respect to surface expression of different gut-homing markers nor were there any differences noted in IFN-γ and IL-17 generation by mononuclear cells isolated among these surgically-manipulated mice. Although we anticipated that LTβ(-/-) x RAG(-/-) mice would contain functional MLNs but be devoid of GALT and peripheral lymph nodes (PLNs), we found that LTβ(-/-) x RAG(-/-) mice were in fact devoid of MLNs as well as GALT and PLNs. Adoptive transfer of CD45RB(high) T-cells into LTβ(-/-) x RAG(-/-) mice or their littermate controls (LTβ(+/+) x RAG(-/-) ) induced rapid and severe colitis in both groups.

CONCLUSIONS

Taken together, our data demonstrate that: a) neither the GALT, MLNs nor PLNs are required for induction of chronic gut inflammation in this model of IBD and b) T-and/or B-cells may be required for the development of MLNs in LTβ(-/-) mice.

Does allergy impair innate immunity? Leads and lessons from atopic dermatitis

Host defence responses against invading pathogens are well-balanced, inflammatory processes of the innate and adaptive immune system. Impaired development or abnormal function of either system can result in failure to control pathogens and to clear infections. Infections have been claimed to modulate the onset and course of allergic diseases. This so-called hygiene hypothesis is still an active area of research. In contrast, the effects of allergies on infections and pathogen-directed immune responses are less well understood. Here, we have reviewed the existing evidence that allergies result in impaired innate immunity and we discuss recent observations that may explain why and how innate immunity is dysfunctional in allergic patients. With a focus on atopic dermatitis as a model of allergic disease, we speculate that one of the key features of allergic conditions, namely Th2 polarization, leads to several independent inhibitory effects on host defence and consequently to a higher risk of infections in allergic patients. A better understanding of impaired host defence and its mechanisms in allergic subjects will help to improve the management of these diseases.

Subcutaneous infection with S. aureus in mice reveals association of resistance with influx of neutrophils and Th2 response

Staphylococcus aureus is the leading cause of bacterial skin infection. Once it overcomes the epithelial barrier, it either remains locally controlled or spreads in the dermis causing soft tissue infection. These different courses depend not only on its virulence factors, but also on the immune response of the infected individual. The goal of this study was to identify host factors that influence different outcomes. We, therefore, established comparative analysis of subcutaneous footpad infection with S. aureus (SH1000) in different inbred mouse strains. We found that C57BL/6 mice are more susceptible than BALB/c and DBA/2 mice, reflected by significantly higher footpad swelling and bacterial load, as well as increased dissemination of bacteria into inguinal lymph nodes and kidneys. This susceptibility was associated with lower influx of polymorphonuclear leukocytes (PMNs), but higher secretion of CXCL-2. Remarkably, resistance correlated with S. aureus-specific Th2-cell response in BALB/c and DBA/2 mice, whereas susceptible C57BL/6 mice generated a Th1-cell response. As Th1 cells are able to induce release of CXCL-2, and as CXCL-2 is able to increase the survival of S. aureus within PMNs, interactions between PMNs and Th1 or Th2 cells need to be considered as important mechanisms of resistance in murine soft tissue infection with S. aureus.

Pulmonary responses to Stachybotrys chartarum and its toxins: mouse strain affects clearance and macrophage cytotoxicity

We investigated differences in the pulmonary and systemic clearance of Stachybotrys chartarum spores in two strains of mice, BALB/c and C57BL/6J. To evaluate clearance, mice were intratracheally instilled with a suspension of radiolabeled S. chartarum spores or with unlabeled spores. The lungs of C57BL/6J mice showed more rapid spore clearance than the lungs of BALB/c mice, which correlated with increased levels of spore-associated radioactivity in the GI tracts of C57BL/6J as compared with BALB/c mice. To identify mechanisms responsible for mouse strain differences in spore clearance and previously described lung inflammatory responses, we exposed alveolar macrophages (AMs) lavaged from BALB/c and C57BL/6J mice to S. chartarum spores, S. chartarum spore toxin (SST), and satratoxin G (SG) in vitro. The S. chartarum spores were found to be highly toxic with most cells from either mouse strain being killed within 24 h when exposed to a spore:cell ratio of 1:75. The spores were more lethal to AMs from C57BL/6J than those from BALB/c mice. In mice, the SST elicited many of the same inflammatory responses as the spores in vivo, including AM recruitment, pulmonary hemorrhage, and cytokine production. Our data suggest that differences in pulmonary spore clearance may contribute to the differences in pulmonary responses to S. chartarum between BALB/c and C57BL/6J mice. Enhanced AM survival and subsequent macrophage-mediated inflammation may also contribute to the higher susceptibility of BALB/c mice to S. chartarum pulmonary effects. Analogous genetic differences among humans may contribute to reported variable sensitivity to S. chartarum.

Keratinocytes determine Th1 immunity during early experimental leishmaniasis

Experimental leishmaniasis is an excellent model system for analyzing Th1/Th2 differentiation. Resistance to Leishmania (L.) major depends on the development of a L. major specific Th1 response, while Th2 differentiation results in susceptibility. There is growing evidence that the microenvironment of the early affected tissue delivers the initial triggers for Th-cell differentiation. To analyze this we studied differential gene expression in infected skin of resistant and susceptible mice 16h after parasite inoculation. Employing microarray technology, bioinformatics, laser-microdissection and in-situ-hybridization we found that the epidermis was the major source of immunomodulatory mediators. This epidermal gene induction was significantly stronger in resistant mice especially for several genes known to promote Th1 differentiation (IL-12, IL-1β, osteopontin, IL-4) and for IL-6. Expression of these cytokines was temporally restricted to the crucial time of Th1/2 differentiation. Moreover, we revealed a stronger epidermal up-regulation of IL-6 in the epidermis of resistant mice. Accordingly, early local neutralization of IL-4 in resistant mice resulted in a Th2 switch and mice with a selective IL-6 deficiency in non-hematopoietic cells showed a Th2 switch and dramatic deterioration of disease. Thus, our data indicate for the first time that epidermal cytokine expression is a decisive factor in the generation of protective Th1 immunity and contributes to the outcome of infection with this important human pathogen.

To clear skin infections with the parasite Leishmania major, a specific T-helper (Th)-cell immune response has to be generated. The type of Th-cell response is determined early after infection by yet unknown mechanisms. In resistant mice a Th1-pattern is generated. A Th2-pattern in BALB/c mice, however, results in susceptibility. An analysis of these mechanisms is important for a better understanding of both host-parasite interactions and non-infectious Th-cell driven inflammatory skin disorders (e.g. atopic dermatitis). We analyzed how the infected skin influenced the Th-cell response. Therefore, we compared gene-expression early after infection in the skin of resistant and susceptible mice. Several cytokines (like IL-1β, IL-12, osteopontin, IL-4 and IL-6) were more strongly produced in the skin of resistant mice and therefore could be important for Th1-differentiation. We demonstrated that they were expressed by epidermal keratinocytes. Using mice with a deficiency for IL-6 in keratinocytes but not in immune cells and by inhibiting the action of early produced IL-4 we revealed that keratinocyte-derived IL-6 and IL-4 are important for resistance against Leishmania. Thus, our results indicate that the epidermis controls Th1-differentiation and may be a new pharmacological target for modification of Th-differentiation.

Role of secondary lymphoid tissues in primary and memory T-cell responses to a transplanted organ

Secondary lymphoid tissues are the hub of adaptive immune responses wherein rare cognate lymphocytes encounter dendritic cells bearing antigen from peripheral tissues and differentiate into effector and memory cells that eliminate antigen. It is accepted that immune responses against microbial and tumor antigens are initiated within secondary lymphoid tissues. There is less agreement on whether the same principle applies to immune responses to a transplanted organ because an allograft expresses foreign major histocompatibility complex and contains donor antigen presenting cells that could activate T cells directly in situ leading to rejection. Recent studies confirm that although naïve T cells can be primed within the allograft, their differentiation to effect rejection is dependent on secondary lymphoid tissues. Antigen-experienced memory T cells, unlike Naïve T cells, function largely independent of secondary lymphoid tissues to cause allograft rejection. In an alloimmune response, secondary lymphoid tissues support not only immune activation but also immune regulation essential for allograft survival. Here, we will review recent findings and discuss the role of secondary lymphoid tissues in primary and memory alloimmune responses.

PPEF/PP7 protein Ser/Thr phosphatases

PPEF/PP7 represents one of the five subfamilies of the PPP protein Ser/Thr phosphatases. Studies published in recent years point to a role of plant PP7 at a crossroad of different pathways of light and stress signalling. In animals, PPEFs are highly expressed in sensory neurons, and Drosophila PPEF phosphatase, rdgC, is essential for dephosphorylation of rhodopsin. Expression profiling suggests that mammalian PPEF may play a role in stress-protective responses, cell survival, growth, proliferation, and oncogenesis. Despite structural similarities of the catalytic domains and the fact that some of these phosphatases are involved in light perception both in animals and in plants, the plant and non-plant representatives of this group have distinct domain architecture and appear not to be orthologues.