Species differences in the structure and function of the immune system

Ablation of SP-A has a negative impact on the susceptibility of mice to Klebsiella pneumoniae infection after ozone exposure: sex differences

Background

Surfactant protein A (SP-A) enhances phagocytosis of bacteria, including Klebsiella pneumoniae, by alveolar macrophages. Ozone, a major air pollutant, can cause oxidation of surfactant and may influence lung immune function. Immune function may also be affected by sex-specific mechanisms. We hypothesized that ablation of SP-A has a negative impact on the susceptibility of mice to Klebsiella pneumoniae infection after ozone exposure, and that sex differences in the effect of ozone do exist.

Methods

Male and female SP-A (-/-) mice on the C57BL/6J background were exposed to ozone or to filtered air (FA) used as a control and then infected intratracheally with K. pneumoniae bacteria. Survival rate was monitored during a 14-day period. In addition, protein oxidation levels and in vivo phagocytosis were checked 1 h after inoculation of PBS used as a sham control and after inoculation of K. pneumoniae bacteria in PBS, respectively.

Results

We found: 1) ozone exposure followed by K. pneumoniae infection decreases survival and alveolar macrophage phagocytic function of SP-A (-/-) mice compared to filtered air exposure (p < 0.05), and females are more affected than males; 2) SP-A (-/-) mice (exposed either to ozone or FA) are more susceptible to infection with K. pneumoniae than wild type (WT) mice regarding their survival rate and macrophage phagocytic function; the phagocytic function of FA SP-A(-/-) is similar to that of ozone exposed WT. 3) ozone exposure appears to increase infiltration of PMNs, total protein, and SP-A oxidation in WT mice; infiltration of PMNs and total protein oxidation appears to be more pronounced in female mice in response to ozone; 4) ozone exposure increases SP-A oxidation in WT females significantly more than in males.

Conclusion

Absence (i.e. ablation of SP-A in SP-A (-/-) mice) or reduction of functional activity of SP-A (i.e. oxidation of SP-A in WT mice) increases the susceptibility of mice to experimental pneumonia after ozone exposure, and in both cases females are more affected by ozone exposure than males.

Modulation of ovine neutrophil function and apoptosis by standardized extracts of Echinacea angustifolia, Butea frondosa and Curcuma longa

Impaired neutrophil function has been associated with increased infectious diseases in ruminants. Attachment of neutrophils to endothelium and superoxide production is critical features of their immune activity. Once the infection is cleared, programmed cell death ensures the rapid resolution of inflammation. To develop new natural therapeutics for ruminants, standard extracts of Echinacea angustifolia (Polinacea), Butea frondosa and Curcuma longa (Curcuvet) were first evaluated on ovine neutrophil functions. Curcuvet strongly reduced PMA-stimulated adhesion and superoxide production. Polinacea and B. frondosa extract also reduced these functions, but with less efficacy than Curcuvet. We analyzed the effect of extracts on spontaneous apoptosis and gene expression in neutrophils aged in vitro for up to 22h. IL8 is critical for neutrophil recruitment and the immune response; Bcl2-related proteins, Bcl2A1 and Bax, are key regulators of neutrophil fate. Spontaneous apoptosis strongly increased in ovine neutrophils cultured for 22h (T22), accompanied by an upregulation of IL8 and a decreased Bcl2A1:Bax ratio. Curcuvet stimulated spontaneous apoptosis and inhibited IL8 and Bcl2A1 gene expression at T22, whereas Polinacea and B. frondosa extract inhibited spontaneous apoptosis and stimulated IL8 expression at T22. These results suggest that Curcuvet has antiinflammatory activity, whereas Polinacea and B. frondosa have an immunomodulatory action on sheep neutrophils.

Histochemical and molecular overview of the thymus as site for T-cells development

The thymus represents the primary site for T cell lymphopoiesis, providing a coordinated set for critical factors to induce and support lineage commitment, differentiation and survival of thymus-seeding cells. One irrefutable fact is that the presence of non-lymphoid cells through the thymic parenchyma serves to provide coordinated migration and differentiation of T lymphocytes. Moreover, the link between foetal development and normal anatomy has been stressed in this review. Regarding thymic embryology, its epithelium is derived from the embryonic endodermal layer, with possible contributions from the ectoderm. A series of differentiating steps is essential, each of which must be completed in order to provide the optimum environment for thymic development and function. The second part of this article is focused on thymic T-cell development and differentiation, which is a stepwise process, mediated by a variety of stromal cells in different regions of the organ. It depends strongly on the thymic microenvironment, a cellular network formed by epithelial cells, macrophages, dendritic cells and fibroblasts, that provide the combination of cellular interactions, cytokines and chemokines to induce thymocyte precursors for the generation of functional T cells. The mediators of this process are not well defined but it has been demonstrated that some interactions are under neuroendocrine control. Moreover, some studies pointed out that reciprocal signals from developing T cells also are essential for establishment and maintenance of the thymic microenvironment. Finally, we have also highlighted the heterogeneity of the lymphoid, non-lymphoid components and the multi-phasic steps of thymic differentiation. In conclusion, this review contributes to an understanding of the complex mechanisms in which the foetal and postnatal thymus is involved. This could be a prerequisite for developing new therapies specifically aimed to overcome immunological defects, linked or not-linked to aging.

What’s So Special about the Developing Immune System?

The evolution of the subdiscipline of developmental immunotoxicology (DIT) as it exists today has been shaped by significant regulatory pressures as well as key scientific advances. This review considers the role played by legislation to protect children’s health, and on the emergence of immunotoxcity and developmental immunotoxicity guidelines, as well as providing some context to the need for special attention on DIT by considering the evidence that the developing immune system may have unique susceptibilities when compared to the adult immune system. Understanding the full extent of this potential has been complicated by a paucity of data detailing the development of the immune system during critical life stages as well as by the complexities of comparisons across species. Notably, there are differences between humans and nonhuman species used in toxicity testing that include specific differences relative to the timing of the development of the immune system as well as more general anatomic differences, and these differences must be factored into the interpretation of DIT studies. Likewise, understanding how the timing of the immune development impacts on various immune parameters is critical to the design of DIT studies, parameters most extensively characterized to date in young adult animals. Other factors important to DIT, which are considered in this review, are the recognition that effects other than suppression (e.g., allergy and autoimmunity) are important; the need to improve our understanding of how to assess the potential for DIT in humans; and the role that pathology has played in DIT studies in test animals. The latter point receives special emphasis in this review because pathology evaluations have been a major component of standard nonclinical toxicology studies, and could serve an important role in studies to evaluate DIT. This possibility is very consistent with recommendations to incorporate a DIT evaluation into standard developmental and reproductive toxicology (DART) protocols. The overall objective of this review is to provide a ‘snapshot’ of the current state-of-the-science of DIT. Despite significant progress, DIT is still evolving and it is our hope that this review will advance the science.

Animal models of human pneumonia

Pneumonia is a medical and public health priority, and advances against this disease will require improved knowledge of biological mechanisms. Human pneumonia is modeled with experimental infections of animals, most frequently mice. Mouse models are leading to important discoveries relevant to pneumonia, but their limitations must be carefully considered. Several approaches to establishing pneumonia in mice have been developed, and each has specific strengths and weaknesses. Similarly, procedures for characterizing microbial and host responses to infection have unique advantages and disadvantages. Mice are not small humans, and the applicability of results from murine models to human disease depends on understanding the similarities and differences between species. Additional considerations such as mouse strain, microbe strain, and prior mouse-microbe interactions also influence the design and interpretation of experiments. Results from studies of pneumonia in animals, combined with complementary basic and translational studies, are elucidating mechanisms responsible for susceptibility to and pathophysiology of lung infection.

Effects of housing condition on experimental outcome in a reproduction toxicity study

In most toxicity studies single housing is still preferred, as social stress is believed to have an effect on experimental outcome through interaction with the toxic compound or by increasing variation. There are also arguments that single housing will have a similar effect. In this study the qualitative and quantitative effects of single- and social housing of rats has been investigated on immune- and endocrine responses, histopathology and body- and organ weights in a one-generation endocrine disrupter study (OECD 415) in rats exposed to tetrabromobisphenol A (TBBPA). The results of this study show that differences in parameters between the housing conditions were rarely noted. Striking results of the study are that in several parameters significant differences were noted in the un-dosed control group in single versus group housed animals, meaning that TBBPA can mask or enhance housing effects, or vice versa. In one case single housing altered the effect of the toxic compound. Depending on the endpoints of the study, the type of housing condition must be taken into consideration as findings like these could have great implications for the interpretation and validity of results from toxicological assays and the number of animals needed to detect significant effects of toxic compounds.

Mucosal inoculation with an attenuated mouse pneumovirus strain protects against virulent challenge in wild type and interferon-gamma receptor deficient mice

Protective mechanisms underlying the responses to mucosal vaccination are not yet clearly defined. Using the natural mouse pneumovirus pathogen, pneumonia virus of mice (PVM), we explore responses of wild type and interferon-gamma (IFNgamma) receptor gene-deleted mice to virulent challenge after mucosal vaccination with an attenuated virus strain. Serum neutralizing antibodies develop after intranasal inoculation with 30 pfu of attenuated, replication-competent PVM strain 15, which correlate with diminished gross and microscopic pulmonary pathology and protection from weight loss in response to subsequent challenge with the virulent parent PVM strain J3666. Virus replication in response to challenge was blunted in PVM strain 15 vaccinated mice, as was local production of secretory mediators IFNgamma, TNF-alpha, MIP-1 alpha, and MIP-2. Interestingly, responses of vaccinated IFNgamma receptor gene-deleted mice were indistinguishable from those of the wild type, suggesting that IFNgamma signaling may not be crucial for the generation of adaptive responses to pneumovirus infection in vivo.

Methodologies for developmental immunotoxicity (DIT) testing

Developmental immunotoxicity has gained increasing recognition as a significant factor influencing the risk of later life disease. Based on the data collected thus far on different chemicals and drugs, the developing immune system can be significantly more sensitive than the adult immune system to xenobiotic-induced insult. There are distinct differences between the immune system surrounding birth and that in the mature adult as well as differences in the nature of immunotoxic changes based on age. Immunosuppresssion is not the only concern. Immunotoxic changes that increase the risk for allergic or autoimmune responses should also be considered. Therefore, one should not assume that immunotoxicity assays validated for adult exposure assessment are inherently the most predictive for developmental immunotoxicology (DIT) evaluation. Many of those adult-based protocols were developed solely to detect immunosuppression, whereas DIT concerns include shifts in immune balance. For this reason, it is useful to examine the various immune endpoints that have been employed in recent perinatal immunotoxicity studies, compare those against routine adult immunotoxicity evaluation protocols, and consider the options that are available for effective DIT testing. The results published on several chemicals and drugs in recent years suggest that functional tests are a front-line priority for perinatal immunotoxicity detection and that a combination of at least two functional tests (such as a multi-isotype T-dependent antibody response (TDARs), and a cell-mediated immune response assay such as the delayed-type hypersensitivity assay and/or T cell or NK cytotoxicity assays) should be paired with immune cell populations and histopathological analysis. Cytokine production measurements offer outstanding promise and may eventually be able to be substituted for other more laborious procedures. However, multi-cytokine analysis needs to be standardized in terms of optimum source for analysis and protocol.

Histopathology of the thymus

The thymus is a primary lymphoid organ that manifests dynamic physiological changes as animals age in addition to being exquisitely sensitive to stress and toxic insult. It is typically the first lymphoid tissue to respond to immunotoxic xenobiotics, with the first change being loss of cortical lymphocytes by apoptosis. This is followed by removal of the apoptotic cellular debris and, in the absence of recovery, may lead to loss of the cortico-medullary demarcation and organ atrophy. Nonneoplastic proliferative changes include focal lymphoid hyperplasia and proliferation of medullary epithelial cells, often with formation of ribbons, cords, or tubules. Thymomas are relatively rare tumors that exhibit a wide spectrum of morphologic types but do not metastasize. Thymic lymphomas are common in some mouse strains and can become leukemic with hematogenous spread throughout the body.

Enhanced histopathology of mucosa-associated lymphoid tissue

The secretory epithelial surfaces of the body are a major route of entry for potentially pathogenic substances. The organized mucosal lymphoid tissues that are found within the gastrointestinal and respiratory tracts are therefore particularly important as a first line of defense against harmful compounds. The major function of these mucosa-associated lymphoid tissues (MALT) is to initiate local IgA immune responses, which are then passed on to draining lymph nodes. For enhanced histopathology, the separate compartments of each lymphoid tissue should be evaluated separately for changes in size and lymphocyte cellularity and descriptive rather than interpretive terminology should be used to characterize any changes. The organization of MALT is similar to that of lymph nodes with B-cell-rich follicles and T-cell-rich interfollicular areas. Therefore, these two compartments should be evaluated separately for changes in size and lymphocyte cellularity and the germinal center development within lymphoid follicles should be evaluated as well.

Normal structure, function, and histology of mucosa-associated lymphoid tissue

The mucosa-associated lymphoid tissue (MALT) initiates immune responses to specific antigens encountered along all mucosal surfaces. MALT inductive sites are secondary immune tissues where antigen sampling occurs and immune responses are initiated. Effector sites, present as diffuse lymphoid tissue along all mucosal surfaces are the sites of IgA transport across the mucosal epithelium. Though there are many differences between inductive sites in various organs, they all contain the same basic compartments-follicles, interfollicular regions, subepithelial dome regions, and follicle-associated epithelium. The morphologic differences between MALT and other secondary lymphoid tissues, between the MALT sites of differing anatomic locations, and species differences among laboratory animals are described. The morphologic changes in MALT associated with aging, route of nutrition, and genetic mutation (i.e., the nude and SCID mutations) are also discussed. MALT tissues comprise the mucosal immune system which can function independently of the systemic immune system and are, therefore, an important and often overlooked aspect of immunopathology.

Normal structure, function and histology of the thymus

The thymus, a primary lymphoid organ and the initial site for development of T cell immunological function, is morphologically similar across species. It is actually an epithelial organ in which its epithelial cells provide a framework containing T cells as well as smaller numbers of other lymphoid cells. A symbiotic interaction exists between the thymic microenvironment and developing T cells, and the specificity of T cell release into the systemic circulation is under thymic control. The thymic cortex in a young animal is heavily populated by developing T cells along with a smaller proportion of associated epithelial cells. Larger, more mature T cells are found in the medulla where epithelial and other cell types are more abundant. Understanding normal morphological features of the thymus and their perturbations provides a cornerstone to assessing immune system function.

Epitope characterization of ovalbumin in BALB/c mice using different entry routes

Ovalbumin (OVA) is known as a major allergen in egg white. A number of studies have reported the partial T and B cell epitope mapping of OVA using murine models and allergic patients' sera. Recently, we have reported the IgE-binding regions of the entire OVA molecule using egg allergic patients' sera. However, the entire epitope mapping of OVA in a murine model has not been completed yet. In the present study, BALB/c mice were administered a solution of OVA using three different entry routes (oral, intraperitoneal and subcutaneous) with their respective adjuvant (cholera toxin, aluminum hydroxide and Freund's adjuvant). Two nitrocellulose membranes containing 188 overlapping synthetic peptides (with a length of 12 amino acids and an offset of two amino acids) covering the primary sequence of OVA, were probed with the three different BALB/c mice antisera. Antisera obtained from orally challenged mice identified eight IgE epitope regions, i.e. I53D60; V77R84; S103E108; G127T136; E275V280; G301F306; I323A332 and A375S384, while sera raised by intraperitoneal and subcutaneous injections exhibited two (K55D60 and K277L282) and five (K55R58; G127T136; K279L282; T303S308 and I323A332) IgE binding sequences, respectively. The residues critical for the epitope-paratope interactions were finely characterized using the oral immunization serum. Analysis of IgE binding epitopes in mice provides us with potential strategies for design of specific immunotherapy.

Morphometrical Characteristics of Age-Associated Changes in the Thymus of Old Male Wistar Rats

In order to provide a morphometrical description of the changes in the aged rat thymus and to relate them to apoptotic and proliferative activity of thymocytes, the thymuses from 3- and 18-month-old male Wistar rats and the percentages of bromodeoxyuridine-incorporating and apoptotic cells in cultures of thymocytes were assessed by stereological analysis and flow cytometry, respectively. In old rats the volume of lymphoepithelial thymic tissue is markedly reduced, reflecting a sharp decrease in the total number of thymocytes. A reduction in the proliferative capacity of thymocytes and increase in their susceptibility to apoptosis are, most likely, primarily responsible for a 7-fold reduction in thymic cellularity in old animals. Furthermore, only the volume of cortical compartment was affected by aging, while that of medulla, despite of reduced cellularity, was not significantly altered. The loss of functional tissue in aged thymus is compensated by a substantial increase in the volume of inter-lobular connective and adipose tissue, so the thymic weight remained unaltered in old rats. These results suggest that thymus of aged Wistar rats exhibits morphological characteristics similar to those found in aged human thymus and thus may serve as an animal model for further investigations of thymus-related changes in immunological aging.

Elasmobranch immune cells as a source of novel tumor cell inhibitors: Implications for public health

SYNOPSIS: Reports that elasmobranchs (sharks, skates, and rays) may have a low incidence of disease have stimulated interest in understanding the role of their immune system in this apparent resistance. Although research in this area may potentially translate into applications for human health, a basic understanding of the elasmobranch immune system components and how they function is essential. As in higher vertebrates, elasmobranch fishes possess thymus and spleen, but in the absence of bone marrow and lymph nodes, these fish have evolved unique lymphomyeloid tissues, namely epigonal and Leydig organs. As conditions for short-term culture of elasmobranch immune cells have become better understood, the opportunity to examine functional activity of cytokine-like factors derived from conditioned culture medium has resulted in the identification of growth inhibitory activity against a variety of tumor cell lines. Specifically, the medium enriched by short term culture of bonnethead shark (Sphyrna tiburo) epigonal cells (epigonal conditioned medium, ECM) has been shown to inhibit the growth of mammalian tumor cell lines, including fibrosarcoma (WEHI-164), melanoma (A375.S2), B-cell lymphoma (Daudi), T-cell leukemia (Jurkat), pancreatic cancer (PANC-1), ovarian cancer (NIH:OVCAR-3), and three breast carcinoma cell lines (MCF7, HCC38, Hs578T). Of the cell lines tested, WEHI-164, A375.S2, Daudi, and Jurkat cells were among the most sensitive to growth inhibitory activity of ECM whereas PANC-1 and NIH:OVCAR-3 cells were among the least sensitive. In addition, ECM demonstrated preferential growth inhibition of malignant cells in assays against two different malignant/non-malignant cell line pairs (HCC38/HCC38 BL and Hs 578T/Hs 578Bst). Separation of protein components of ECM using SDS-PAGE resulted in a very reproducible pattern of three major bands corresponding to molecular sizes of approximately 40-42 kD, 24 kD, and 17 kD. Activity is lost after heating at 75 degrees C for 30 min, and can be diminished by treatment with proteinase K and protease. Activity is not affected by treating with trypsin, DNase I or RNase A.

The immune system as a target for environmental chemicals: Xenoestrogens and other compounds

The immune system in higher organisms is under integrated control and has the capacity to rapidly respond to the environment. Recently, there has been a significant increase in the prevalence of allergic diseases. Environmental factors likely play a major role in the explosion of allergy. Although the "hygiene hypothesis" may explain the increase in allergic diseases which are prone to T helper 2 (Th2) immune responses, recent findings highlight the possible involvement of environmental xenobiotic chemicals which can modulate normal immune function. Interestingly, several reports suggest that the prevalence of systemic lupus erythematosus, a Th2-type autoimmune disease, is also increasing, although the development of high-sensitivity immunological tests may be a possible cause. The increased prevalence of autoimmune disease in women, the sexual dimorphism of the immune response, and the immunomodulatory effects of sex steroids, have focused attention on the role of chemicals which influence sex steroids in the development of immune diseases. Moreover, recent reports indicate that some environmental chemicals can work on nuclear hormone receptors, other than sex hormone receptors, and modulate immune reactions. This review focuses on the impact of environmental chemicals on immune system function and pathogenesis of immune diseases, including allergy and autoimmune diseases.

Contemplating the murine test tube: lessons from natural killer cells andCryptococcus neoformans

Murine experimentation has provided many useful tools, including the ability to knockout or over-express genes and to perform experiments that are limited by ethical considerations. Over the past century, mice have imparted valuable insights into the biology of many systems, including human immunity. However, although there are many similarities between the immune response of humans and mice, there are also many differences; none is more prominent than when examining natural killer cell biology. These differences include tissue distribution, effector molecules, receptor repertoire, and cytokine responses, all of which have important implications when extrapolating the studies to the human immune responses to Cryptococcus neoformans.

Immunotoxicology: role in the safety assessment of drugs

The immunotoxic effects of drugs are divided into immunosuppression, immunostimulation, hypersensitivity and autoimmunity. The major adverse consequences of immunosuppression are infectious complications and virus-induced malignancies. Flu-like reactions, more frequent autoimmune diseases and hypersensitivity reactions to unrelated allergens, and inhibition of drug-metabolising enzymes are the adverse effects related to immunostimulation. Hypersensitivity reactions are the most frequent immunotoxic effects of drugs. They include immune-mediated ('allergic') and non immune-mediated ('pseudoallergic') reactions. Drug-induced autoimmune reactions, either systemic or organ-specific, are seemingly rare. A review of drug-induced immunotoxic effects demonstrates that immunotoxicity is a significant cause of morbidity and even mortality. As immunotoxicologists have long focused on immunosuppression, the nonclinical immunotoxicity safety assessment of unexpected immunosuppression is based on a number of relatively well standardised and validated animal models and assays. However, there is no general consensus regarding the minimal requirement for this assessment. Many different assays can be used to extend the assessment case by case. Few animal models and assays have been validated for use in the nonclinical safety assessment of unexpected immunostimulation. The situation is worse regarding the prediction of hypersensitivity and autoimmune reactions. Our limited understanding of the molecular and cellular mechanisms of immunotoxicity accounts, at least partly, for this situation. Recent guidelines for the immunotoxicity safety assessment of drugs, even though conflicting on several points, will serve as an impetus not only to refine current animal models and assays, but also to search for better alternatives. The new data generated will have to be interpreted and extended to animal species other than just rodents. Likewise, animal results will have to be compared with findings in humans. The search for immunological endpoints that can be used in several animal species and in humans will therefore become essential. Specific endpoints and clinical criteria that can be included in clinical trials to further investigate the potential for immunotoxicity of new drugs will have to be defined. Because immunotoxicity plays a key role in drug-induced adverse effects, the role of immunotoxicology in drug safety assessment is indisputable and the systematic nonclinical as well as clinical immunotoxicity assessment of every new drug is deemed essential.

Regulatory immunotoxicology: does the published evidence support mandatory nonclinical immune function screening in drug development?

Recent immunotoxicity guidance documents from the EU CHMP and the US FDA apply significantly different weightings to immune function testing; whereas the former mandates (as a starting point) incorporation of immune function tests (IFTs) to screen for immunotoxic potential in sub-chronic rodent toxicity studies, the more cautious 'for cause' FDA approach recommends the use of IFTs only when warranted by evidence obtained from conventional nonclinical and/or clinical studies. Conclusions from detailed evaluations of several key drugs, including salmeterol and some opioids, challenge the notion that data on these examples support the need for IFTs to detect unintended immunosuppression. Given the virtual absence of convincing pharmaceutical examples and the rarity of unintended immunosuppression, routine immune function testing of all new pharmaceuticals is not considered justified. Resources currently being employed in this manner in an attempt to detect a seemingly rare phenomenon would appear to be better applied to the development of reliable predictive assays for drug hypersensitivity, which is known to cause significant patient morbidity. Any moves towards a globally harmonised guideline that recommends the use of concern-based IFTs, need ideally to be accompanied by the establishment of appropriate historical control reference intervals and interpretation criteria to support a reliable weight-of-evidence approach to data evaluation.

Of mice and not men: differences between mouse and human immunology

Mice are the experimental tool of choice for the majority of immunologists and the study of their immune responses has yielded tremendous insight into the workings of the human immune system. However, as 65 million years of evolution might suggest, there are significant differences. Here we outline known discrepancies in both innate and adaptive immunity, including: balance of leukocyte subsets, defensins, Toll receptors, inducible NO synthase, the NK inhibitory receptor families Ly49 and KIR, FcR, Ig subsets, the B cell (BLNK, Btk, and lambda5) and T cell (ZAP70 and common gamma-chain) signaling pathway components, Thy-1, gammadelta T cells, cytokines and cytokine receptors, Th1/Th2 differentiation, costimulatory molecule expression and function, Ag-presenting function of endothelial cells, and chemokine and chemokine receptor expression. We also provide examples, such as multiple sclerosis and delayed-type hypersensitivity, where complex multicomponent processes differ. Such differences should be taken into account when using mice as preclinical models of human disease.