ATPase and MHC class II molecules co-expression in Rana pipiens dendritic cells

Immunohistochemical Characterization of Langerhans Cells in the Skin of Three Amphibian Species

The amphibian taxon includes three orders that present different morphological characteristics: Anura, Caudata, and Apoda. Their skin has a crucial role: it acts as an immune organ constituting a physical, chemical, immunological, and microbiological barrier to pathogen insult and conducts essential physiological processes. Amphibians have developed specialized features to protect the vulnerable skin barrier, including a glandular network beneath the skin surface that can produce antimicrobial and toxic substances, thus contributing to the defense against pathogens and predators. This study aims to characterize Langerhans cells in the skin of Lithobates catesbeianus (order: Anura; Shaw, 1802), Amphiuma means (order: Caudata; Garden, 1821), and Typhlonectes natans (order: Apoda; Fischer, 1880) with the following antibodies: Langerin/CD207 (c-type lectin), Major Histocompatibility Complex (MHC)II, and Toll-like receptor (TLR)2 (expressed by different types of DCs). Our results showed Langerhans cells positive for Langerin CD/207 in the epidermis of the three species; moreover, some antigen-presenting cells (APCs) in the connective tissue expressed TLR2 and MHCII. The distribution of the Langerhans cells is very similar in the three amphibians examined, despite their different habitats. A greater knowledge of the amphibian immune system could be useful to better understand the phylogeny of vertebrates and to safeguard amphibians from population declines. Furthermore, the similarities between amphibians' and human skin concerning immunological features may be useful in both biology and translational medicine.

The adaptive microbiome hypothesis and immune interactions in amphibian mucus

The microbiome is known to provide benefits to hosts, including extension of immune function. Amphibians are a powerful immunological model for examining mucosal defenses because of an accessible epithelial mucosome throughout their developmental trajectory, their responsiveness to experimental treatments, and direct interactions with emerging infectious pathogens. We review amphibian skin mucus components and describe the adaptive microbiome as a novel process of disease resilience where competitive microbial interactions couple with host immune responses to select for functions beneficial to the host. We demonstrate microbiome diversity, specificity of function, and mechanisms for memory characteristic of an adaptive immune response. At a time when industrialization has been linked to losses in microbiota important for host health, applications of microbial therapies such as probiotics may contribute to immunotherapeutics and to conservation efforts for species currently threatened by emerging diseases.

Do immune system changes at metamorphosis predict vulnerability to chytridiomycosis? An update

Amphibians are among the vertebrate groups suffering great losses of biodiversity due to a variety of causes including diseases, such as chytridiomycosis (caused by the fungal pathogens Batrachochytrium dendrobatidis and B. salamandrivorans). The amphibian metamorphic period has been identified as being particularly vulnerable to chytridiomycosis, with dramatic physiological and immunological reorganisation likely contributing to this vulnerability. Here, we overview the processes behind these changes at metamorphosis and then perform a systematic literature review to capture the breadth of empirical research performed over the last two decades on the metamorphic immune response. We found that few studies focused specifically on the immune response during the peri-metamorphic stages of amphibian development and fewer still on the implications of their findings with respect to chytridiomycosis. We recommend future studies consider components of the immune system that are currently under-represented in the literature on amphibian metamorphosis, particularly pathogen recognition pathways. Although logistically challenging, we suggest varying the timing of exposure to Bd across metamorphosis to examine the relative importance of pathogen evasion, suppression or dysregulation of the immune system. We also suggest elucidating the underlying mechanisms of the increased susceptibility to chytridiomycosis at metamorphosis and the associated implications for population persistence. For species that overlap a distribution where Bd/Bsal are now endemic, we recommend a greater focus on management strategies that consider the important peri-metamorphic period.

Epicutaneous Administration of 17β-Estradiol Induces Langerhans Cells Depletion

BACKGROUND

Langerhans cells (LC) number and function in mouse vaginal mucosa are affected by 17β-estradiol (E₂) application; nonetheless, its effect on epidermal LC has not been studied. The purpose of this study was to evaluate the effect of topical administration of E₂ on the number, phenotype, and migratory ability of LC in mouse skin.

METHODS

Ears of adult CD1 male mice were topically treated once with several doses. Immunohistochemical staining for CD207 and TUNEL staining were performed. LC migration to lymph nodes and the effect on the expression of costimulatory molecules on cultured dendritic cells (DC) were also evaluated.

RESULTS

E₂ decreased the number of CD207+ LC in a dose-dependent manner. One hour after treatment, 1 and 10 µg/mL E₂ significantly reduced the LC number by 21% and 26%, respectively, after two hours, the reduction was 23% and 41%, respectively. After 48 hours, LC recovered, and after 96 hours of treatment, the CD207+/MHCII+ DC numbers were increased in regional lymph nodes. However, CD86 and CD40 molecules were expressed at lower levels than in positive control. The TUNEL assay did not show apoptotic cells. Furthermore, in cultured DC, E₂ promoted a decrease in CD40 and CD86 expression and an increase in CD273, CD274, MHCII, and CCR7.

CONCLUSIONS

The topical administration of E₂ induced a transitory local diminution of LC population and a tolerogenic phenotype. This decrease in epidermal LC suggests that E₂ may affect skin immune responses, inducing an inhibitory response, which should be considered when prescribing topical E₂ medications.

Immunohistochemical characterization of epidermal dendritic-like cells in giant mudskipper, Periophthalmodon schlosseri

Giant Mudskipper, Periophthalmodon schlosseri (Pallas, 1770), is euryhaline, amphibious, and air-breathing fish. These fishes live in close association to mangrove forests and often spend over 90% of time out of water, in adjacent mudflats. They have developed morphological and physiological adaptations to satisfy their unique lifestyles. The skin is the primary interface between the body and the environment, and has a central role in host defence. The initiation of immune responses to antigens in the vertebrate skin has often been attributed to epidermal Langerhans'cells (LC) that are dendritic cells (DC), antigen-presenting cells (APC) which reside in the epidermis. Dendritic cells have been characterized morphologically and functionally in the teleost fish tissues such as rainbow trout, salmonids, medaka, African catfish and zebrafish. However, there is no evidence of the presence of DCs and their role in mudskippers immunity. The aim of this preliminary study was to characterize, through use of specific antibodies: Toll-like receptor 2, S100, serotonin (5-HT), and Vesicular acetylcholine transporter VAChT, a specific DC-like subpopulation in Pn. schlosseri's epidermis.

Microbiota and mucosal immunity in amphibians

We know that animals live in a world dominated by bacteria. In the last 20 years, we have learned that microbes are essential regulators of mucosal immunity. Bacteria, archeas, and viruses influence different aspects of mucosal development and function. Yet, the literature mainly covers findings obtained in mammals. In this review, we focus on two major themes that emerge from the comparative analysis of mammals and amphibians. These themes concern: (i) the structure and functions of lymphoid organs and immune cells in amphibians, with a focus on the gut mucosal immune system; and (ii) the characteristics of the amphibian microbiota and its influence on mucosal immunity. Lastly, we propose to use Xenopus tadpoles as an alternative small-animal model to improve the fundamental knowledge on immunological functions of gut microbiota.

Scar-free wound healing and regeneration in amphibians: immunological influences on regenerative success

Salamanders and frogs are distinct orders of Amphibians with very different immune systems during adult life, exhibiting varying potential for scar free repair and regeneration. While salamanders can regenerate a range of body parts throughout all stages of life, regeneration is restricted to early stages of frog development. Comparison of these two closely related amphibian orders provides insights into the immunological influences on wound repair, and the different strategies that have evolved either to limit infection or to facilitate efficient regeneration. After injury, cells of the immune system are responsible for the removal of damaged cells and providing a cohort of important growth factors and signaling molecules. Immune cells not only regulate new vessel growth important for supplying essential nutrients to damaged tissue but, modulate the extracellular matrix environment by regulating fibroblasts and the scarring response. The profile of immune cell infiltration and their interaction with local tissue immune cells directly influences many aspects of the wound healing outcomes and can facilitate or prevent regeneration. Evidence is emerging that the transition from wound healing to regeneration is reliant on immune cell engagement and that the success of regeneration in amphibians may depend on complex interactions between stem cell progenitors and immune cell subsets. The potential immunological barriers to mammalian regeneration are discussed with implications for the successful delivery of stem cell therapeutic strategies in patients.

Changes in the inflammatory response to injury and its resolution during the loss of regenerative capacity in developing Xenopus limbs

Tissue and organ regeneration, unlike development, involves an injury that in postembryonic animals triggers inflammation followed by resolution. How inflammation affects epimorphic regeneration is largely uninvestigated. Here we examine inflammation and its resolution in Xenopus laevis hindlimb regeneration, which declines during larval development. During the first 5 days postamputation, both regeneration-competent stage 53 and regeneration-deficient stage 57 hindlimbs showed very rapid accumulation of leukocytes and cells expressing interleukin-1β and matrix metalloproteinase 9. Expression of genes for factors mediating inflammatory resolution appeared more persistent at stages 55 and 57 than at stage 53, suggesting changes in this process during development. FoxP3, a marker for regulatory T cells, was upregulated by amputation in limbs at all three stages but only persisted at stage 57, when it was also detected before amputation. Expression of genes for cellular reprogramming, such as SALL4, was upregulated in limbs at all 3 stages, but markers of limb patterning, such as Shh, were expressed later and less actively after amputation in regeneration-deficient limbs. Topical application of specific proinflammatory agents to freshly amputated limbs increased interleukin-1β expression locally. With aqueous solutions of the proinflammatory metal beryllium sulfate, this effect persisted through 7 days postamputation and was accompanied by inhibition of regeneration. In BeSO₄-treated limbs expression of markers for both inflammation and resolution, including FoxP3, was prolonged, while genes for cellular reprogramming were relatively unaffected and those for limb patterning failed to be expressed normally. These data imply that in Xenopus hindlimbs postamputation inflammation and its resolution change during development, with little effect on cellular dedifferentiation or reprogramming, but potentially interfering with the expression of genes required for blastema patterning. The results suggest that developmental changes in the larval anuran immune system may be involved in the ontogenetic loss of epimorphic regeneration in this system.

The developing Xenopus limb as a model for studies on the balance between inflammation and regeneration

The roles of inflammation and immune cell reactivity triggered by amputation have only recently begun to be addressed in investigations of epimorphic regeneration, although studies of tissue repair in mammals clearly show the importance of the immune system in determining the quality of the repair process. Here, we first review inflammation-related work in non-mammalian systems of epimorphic regeneration which suggests that regeneration of an amputated appendage requires continuous modulation of the local immune response, from the first hours after amputation through the period of blastema patterning. We then present data on the effects of anti-inflammatory and proinflammatory agents on regeneration of larval Xenopus hindlimbs. Treatment with the glucocorticoid beclomethasone immediately after amputation inhibits regeneration in regeneration-complete stage 53 limbs. Other anti-inflammatory agents, including the inhibitors of cyclooxygenase-2 (COX-2) activity celecoxib and diclofenac, applied similarly to larvae amputated at stage 55, when the capacity for limb regeneration is normally being lost, restore regenerative capacity. This suggests that although injury-related events sensitive to glucocorticoids are necessary for regeneration, resolution of the inflammatory response may also be required to allow the complete regenerative response and normal blastema patterning. Conversely, if resolution of inflammation is prevented by local treatment of amputated limbs with beryllium, a strong immunoadjuvant, regeneration is inhibited, and gene expression data suggest that this inhibition results from a failure of normal blastema patterning. Both positive and negative effects of immune- or inflammation-related activities occur during anuran limb regeneration and this underscores the importance of considering immune cells in studies of epimorphic regeneration.

Antimicrobial peptides from amphibians

Increased prevalence of multi-drug resistance in pathogens has encouraged researchers to focus on finding novel forms of anti-infective agents. Antimicrobial peptides (AMPs) found in animal secretions are components of host innate immune response and have survived eons of pathogen evolution. Thus, they are likely to be active against pathogens and even those that are resistant to conventional drugs. Many peptides have been isolated and shown to be effective against multi-drug resistant pathogens. More than 500 AMPs have been identified from amphibians. The abundance of AMPs in frog skin is remarkable and constitutes a rich source for design of novel pharmaceutical molecules. Expression and post-translational modifications, discovery, activities and probable therapeutic application prospects of amphibian AMPs will be discussed in this article.

External antigen uptake by Langerhans cells with reorganization of epidermal tight junction barriers

Outermost barriers are critical for terrestrial animals to avoid desiccation and to protect their bodies from foreign insults. Mammalian skin consists of two sets of barriers: stratum corneum (SC) and tight junctions (TJs). How acquisition of external antigens (Ags) by epidermal Langerhans cells (LCs) occur despite these barriers has remained unknown. We show that activation-induced LCs elongate their dendrites to penetrate keratinocyte (KC) TJs and survey the extra-TJ environment located outside of the TJ barrier, just beneath the SC. Penetrated dendrites uptake Ags from the tip where Ags colocalize with langerin/Birbeck granules. TJs at KC–KC contacts allow penetration of LC dendrites by dynamically forming new claudin-dependent bicellular- and tricellulin-dependent tricellular TJs at LC–KC contacts, thereby maintaining TJ integrity during Ag uptake. Thus, covertly under keratinized SC barriers, LCs and KCs demonstrate remarkable cooperation that enables LCs to gain access to external Ags that have violated the SC barrier while concomitantly retaining TJ barriers to protect intra-TJ environment.

Cells of cutaneous immunity in Xenopus: studies during larval development and limb regeneration

The anuran Xenopus laevis is an experimental model for vertebrate development, immunology, and regenerative biology. Using histochemistry and immunohistochemistry (IHC) we examined embryonic, larval, and postmetamorphic Xenopus skin for the presence of dendritic cells (DCs), Langerhans cells (LCs), and dendritic epidermal T cells (DETCs), all components of cutaneous immunity that have been implicated in skin repair and regeneration. Cells expressing three markers for dendritic and Langerhans cells (formalin-resistant ATPase activity, major histocompatibility complex [MHC] class II antigens, and vimentin) and having morphology like that of these cells first appeared during late embryonic stages, becoming abundant by prometamorphosis. Cells positive for these markers were also numerous in the wound epithelia of regenerating hindlimbs at both early and late larval stages. Cells tentatively identified as DETCs were found, beginning at early larval stages, using IHC with antibodies against heterologous CD3epsilon chain and T-cell receptor delta. Further characterization and work with the putative DCs, LCs, and DETCs demonstrated here will allow not only greater understanding of the amphibian immune system, but also further elucidation of regenerative growth and scarring.

Major histocompatibility class II expression in the normal canine cornea and in canine chronic superficial keratitis

OBJECTIVE

To compare the expression of major histocompatibility complex (MHC) class II antigen in the corneas of normal dogs and dogs affected with chronic superficial keratitis (CSK).

METHODS

MHC class II expression was determined in frozen sections of normal canine cornea and cornea from lesions of CSK by immunohistochemistry using a monoclonal antibody directed against the canine MHC class II molecule. Langerhans cell phenotype was determined morphologically and by histochemical determination of ATPase activity. To determine the influence of gamma interferon on expression of MHC class II molecules by corneal cells, corneal explants were cultured with the cytokine and MHC class II expression determined as above.

RESULTS

Numerous MHC class II-expressing cells were demonstrated within the stroma and epithelium of the normal corneal limbus and conjunctival epithelium while very little MHC class II expression was detected in the central region of normal canine cornea. In limbal and conjunctival epithelium, cells expressing MHC class II antigen showed ATPase activity, suggesting that they were Langerhans cells. Corneas from dogs with CSK showed MHC class II expression associated with stromal cells, some of which exhibited a dendritic morphology while most were lymphocytic. Corneal epithelial cells within the lesion also aberrantly expressed MHC class II. Corneal explants expressed MHC class II to varying degrees after differing periods of incubation with the cytokine gamma interferon.

CONCLUSIONS

While the normal central cornea has little MHC class II expression, aberrant expression occurs in CSK, associated with secretion of gamma interferon by infiltrating CD4-expressing lymphocytes. Although this change is likely to be a secondary feature of the CSK lesion, increased MHC class II expression may play a part in perpetuating the corneal inflammation seen in the disease.

Production of rabbit antisera against recombinant MHC class II beta chain and identification of immunoreactive cells in Atlantic salmon (Salmo salar)

In the present work, rabbit antisera recognising the Atlantic salmon (Salmo salar) MHC class II beta chain polypeptide were produced and used in immunoblotting, immunohistochemistry and immunogold electron microscopy. A construct encoding the beta1 and beta2 domains fused to the E. coli protein thioredoxin was used to express the recombinant MHC class II beta chain. Immunoblotting revealed a band of approximately 30kDa in total protein samples from head kidney, spleen, gills, thymus and blood leukocytes, while being absent in muscle. The distribution of MHC class II positive cells was immunohistochemically demonstrated in Atlantic salmon epithelial and haemopoietic tissues. Ultrastructural demonstration of immunoreactive organelles in mid-kidney cells was performed by immunogold electron microscopy. The results indicate expression in lymphocytes, macrophages, epithelial cells and endritic-like cells. This is the first study to address morphological MHC class II expression in a fish species.

Langerhans cell-like dendritic cells in the cornea, tongue and oesophagus of the chicken (Gallus gallus)

Langerhans cells are dendritic leucocytes which reside mainly within stratified squamous epithelia of skin and mucosa. Their visualization requires the use of ATPase histochemistry, electron microscopy for identifying the unique trilaminar cytoplasmic organelles (the Langerhans cell granules or Birbeck granules), and the expression of major histocompatibility complex class II molecules. Following uptake of antigen, Langerhans cells migrate via the afferent lymphatics to the lymph nodes and undergo differentiation from an antigen-processing cell to an antigen-presenting cell. Using the same approach as that employed in previous studies for the identification of chicken epidermal Langerhans cells, we show here the presence of ATPase-positive and major histocompatibility complex class II-positive Langerhans cell-like dendritic cells at the mucosal surface of the eye, tongue and oesophagus of the chicken. Ultrastructurally, these cells qualified as Langerhans cells except that they lack Langerhans cell granules. Thus, as in mammalian skin and mucosa, chicken mucosa contains mucosal dendritic cells with morphological and phenotypical features for the engagement of incoming antigens within epithelium and lamina propria.

Non-specific esterase-positive dendritic cells in epithelia of the frog Rana pipiens

Langerhans cells are antigen-presenting cells located in epithelia and have a dendritic outline, a convoluted nucleus surrounded by an electron lucent cytoplasm with sparse organelles and occasionally containing the characteristic Birbeck granule; their membrane contains class II molecules of the major histocompatibility complex and a strong membrane reactivity for both ATPase and non-specific esterase. Despite increasing knowledge about mammalian Langerhans cells, only a few studies have examined the possible occurrence of Langerhans-like cells in lower vertebrates. Our group has previously demonstrated the presence of dendritic cells in different epithelial membranes co-expressing a strong membrane ATPase reactivity and class II molecules of the major histocompatibility complex in the frog Rana pipiens. Adding another criterion in the characterization of Langerhans-like cells in amphibians, we now report evidence for the expression of membrane non-specific esterase reactivity in dendritic cells located in the epidermis, nictitant membrane and cornea with topographical and light and electron microscopical characteristics identical to those previously described for dendritic cells positive for ATPase and major histocompatibility complex class II in Rana pipiens. We postulate that, taking all this data together, these dendritic intraepithelial cells constitute the amphibian counterpart of mammalian Langerhans cells.