Keratinocytes drive the epithelial hyperplasia key to sea lice resistance in coho salmon.

BACKGROUND: Salmonid species have followed markedly divergent evolutionary trajectories in their interactions with sea lice. While sea lice parasitism poses significant economic, environmental, and animal welfare challenges for Atlantic salmon (Salmo salar) aquaculture, coho salmon (Oncorhynchus kisutch) exhibit near-complete resistance to sea lice, achieved through a potent epithelial hyperplasia response leading to rapid louse detachment. The molecular mechanisms underlying these divergent responses to sea lice are unknown. RESULTS: We characterized the cellular and molecular responses of Atlantic salmon and coho salmon to sea lice using single-nuclei RNA sequencing. Juvenile fish were exposed to copepodid sea lice (Lepeophtheirus salmonis), and lice-attached pelvic fin and skin samples were collected 12 h, 24 h, 36 h, 48 h, and 60 h after exposure, along with control samples. Comparative analysis of control and treatment samples revealed an immune and wound-healing response that was common to both species, but attenuated in Atlantic salmon, potentially reflecting greater sea louse immunomodulation. Our results revealed unique but complementary roles of three layers of keratinocytes in the epithelial hyperplasia response leading to rapid sea lice rejection in coho salmon. Our results suggest that basal keratinocytes direct the expansion and mobility of intermediate and, especially, superficial keratinocytes, which eventually encapsulate the parasite. CONCLUSIONS: Our results highlight the key role of keratinocytes in coho salmon's sea lice resistance and the diverged biological response of the two salmonid host species when interacting with this parasite. This study has identified key pathways and candidate genes that could be manipulated using various biotechnological solutions to improve Atlantic salmon sea lice resistance.

Deletion of Interleukin-4 Receptor Alpha-Responsive Keratinocytes in BALB/c Mice Does Not Alter Susceptibility to Cutaneous Leishmaniasis.

The skin microenvironment at the site of infection plays a role in the early events that determine protective T helper 1/type 1 immune responses during cutaneous leishmaniasis (CL) infection. During CL in nonhealing BALB/c mice, early interleukin-4 (IL-4) can instruct dendritic cells for protective Th1 immunity. Additionally, keratinocytes, which are the principal cell type in the skin epidermis, have been shown to secrete IL-4 early after Leishmania major infection. Here, we investigated whether IL-4/IL-13 signaling via the common IL-4 receptor alpha chain (IL-4Rα) on keratinocytes contributes to susceptibility during experimental CL. To address this, keratinocyte-specific IL-4Rα-deficient (KRT14cre IL-4Rα-/lox) mice on a BALB/c genetic background were generated by gene targeting and site-specific recombination (Cre/loxP) under the control of the keratinocyte-specific krt14 locus. Following high-dose infection with L. major IL-81 and LV39 promastigotes subcutaneously in the footpad, footpad swelling, parasite burden, IFN-γ/IL-4/IL-13 cytokine production, and type 1 and type 2 antibody responses were similar between KRT14cre IL-4Rα-/lox and littermate control IL-4Rα-/lox BALB/c mice. An intradermal infection with low-dose L. major IL-81 and LV39 promastigotes in the ear showed results in infected KRT14cre IL-4Rα-/lox BALB/c mice similar to those of littermate control IL-4Rα-/lox BALB/c mice, with the exception of a significant decrease observed in parasite burden only at the site of LV39 infection in the ear. Collectively, our results show that autocrine and paracrine signaling of IL-4/IL-13 through the IL-4Rα chain on keratinocytes does not influence the establishment of a nonhealing Th2 immune response in BALB/c mice during L. major infection.

Cutaneous histoplasmosis with prominent parasitization of epidermal keratinocytes: report of a case.

Disseminated histoplasmosis most commonly occurs in immunosuppressed individuals and involves the skin in approximately 6% of patients. Cutaneous histoplasmosis with an intraepithelial-predominant distribution has not been described. A 47-year-old man was admitted to our institution with fever and vancomycin-resistant enterococcal bacteremia. He had been diagnosed with T-cell prolymphocytic leukemia 4 years earlier and had undergone matched-unrelated-donor stem cell transplant 2 years earlier; on admission, he had relapsed disease. His medical history was significant for disseminated histoplasmosis 6 months before admission, controlled with multiple antifungal regimens. During this final hospitalization, the patient developed multiple 2-5 mm erythematous papules, a hemorrhagic crust across the chest, shoulders, forearms, dorsal aspect of the fingers, abdomen and thighs. Skin biopsy revealed clusters of oval yeast forms mostly confined to the cytoplasm of keratinocytes and within the stratum corneum; scattered organisms were present in the underlying superficial dermis without any significant associated inflammatory infiltrate. Special stains and immunohistochemical studies confirmed these to be Histoplasma organisms. We highlight this previously unrecognized pattern of cutaneous histoplasmosis to ensure its prompt recognition and appropriate antifungal therapy.

Development and application of three-dimensional skin equivalents for the investigation of percutaneous worm invasion.

Investigation of percutaneous helminth infection is generally based on animal models or excised skin. As desirable replacement of animal experiments, tissue-engineered skin equivalents have recently been applied in microbial and viral in vitro infection models. In the present study, the applicability of tissue-engineered skin equivalents for the investigation of percutaneous helminth invasion was evaluated. Epidermal and a full-thickness skin equivalents that suit the requirements for helminth invasion studies were developed. Quantitative invasion assays were performed with the skin-invading larvae of the helminths Strongyloides ratti and Schistosoma mansoni. Both skin equivalents provided a physical barrier to larval invasion of the nematode S. ratti, while these larvae could invade and permeate a cell-free collagen scaffold and ex vivo epidermis. In contrast, the epidermal and full-thickness skin equivalents exhibited a human host-specific susceptibility to larvae of trematode S. mansoni, which could well penetrate. Invasion of S. mansoni in cell-free collagen scaffold was lowest for all experimental conditions. Thus, reconstructed epidermis and full-thickness skin equivalents confirmed a high degree of accordance to native tissue. Additionally, not only tailless schistosomula but also cercariae could permeate the skin equivalents, and thus, delayed tail loss hypothesis was supported. The present study indicates that the limitations in predictive infection test systems for human-pathogenic invading helminths can be overcome by tissue-engineered in vitro skin equivalents allowing a substitution of the human skin for analysis of the interaction between parasites and their hosts' tissues. This novel tissue-engineered technology accomplishes the endeavor to save animal lives.

In vitro growth, cytopathic effects and clearance of monolayers by clinical isolates of Balamuthia mandrillaris in human skin cell cultures.

Balamuthia mandrillaris is a free-living ameba (FLA) that has been isolated or its DNA identified in soil, dust and water. It causes a fatal central nervous system infection in humans and animals. Although it is environmental as Acanthamoeba and Naegleria fowleri, the two other free-living amebae that also cause CNS infections in humans and other animals, Balamuthia does not feed on bacteria as the other FLA. In the laboratory, it can be grown on a variety of mammalian cell cultures. In this study we examined the ability of three different Balamuthia isolates to grow on several different human skin cell cultures including the WT/A keratinocyte cell cultures. A corneal isolate of Acanthamoeba castellanii was used for comparison.

Antimicrobial activity of NK cells to Trypanosoma cruzi infected human primary Keratinocytes.

Infection with the protozoan parasite Trypanosoma cruzi is causative for Chagas disease, which is a highly neglected tropical disease prevalent in Latin America. Humans are primary infected through vectorial transmission by blood-sucking triatomine bugs. The parasite enters the human host through mucous membranes or small skin lesions. Since keratinocytes are the predominant cell type in the epidermis, they play a critical role in detecting disruptions in homeostasis and aiding in pathogen elimination by the immune system in the human skin as alternative antigen-presenting cells. Interestingly, keratinocytes also act as a reservoir for T. cruzi, as the skin has been identified as a major site of persistent infection in mice with chronic Chagas disease. Moreover, there are reports of the emergence of T. cruzi amastigote nests in the skin of immunocompromised individuals who are experiencing reactivation of Chagas disease. This observation implies that the skin may serve as a site for persistent parasite presence during chronic human infection too and underscores the significance of investigating the interactions between T. cruzi and skin cells. Consequently, the primary objective of this study was to establish and characterize the infection kinetics in human primary epidermal keratinocytes (hPEK). Our investigation focused on surface molecules that either facilitated or hindered the activation of natural killer (NK) cells, which play a crucial role in controlling the infection. To simulate the in vivo situation in humans, an autologous co-culture model was developed to examine the interactions between T. cruzi infected keratinocytes and NK cells. We evaluated the degranulation, cytokine production, and cytotoxicity of NK cells in response to the infected keratinocytes. We observed a strong activation of NK cells by infected keratinocytes, despite minimal alterations in the expression of activating or inhibitory ligands on NK cell receptors. However, stimulation with recombinant interferon-gamma (IFN-γ), a cytokine known to be present in significant quantities during chronic T. cruzi infections in the host, resulted in a substantial upregulation of these ligands on primary keratinocytes. Overall, our findings suggest the crucial role of NK cells in controlling acute T. cruzi infection in the upper layer of the skin and shed light on keratinocytes as potential initial targets of infection.

Visceral leishmaniasis revealed by a squamous cell carcinoma in an HIV-1 infected patient.

We present a case of visceral leishmaniasis confirmed after the histological investigation of an ulcerate lesion of the scalp in an HIV-1-infected patient receiving highly active antiretroviral therapy (HAART). Histological examination of the skin lesion revealed a squamous cell carcinoma superinfected by amastigotes of Leishmania infantum from the bloodstream. Because HIV-1-infected individuals can harbour parasitic infections in normal and neoplastic tissue, it is necessary to examine carefully any skin lesions, particularly those with uncommon aspects or a worsening course, to exclude superinfections by unsuspected pathogens.

The Impact of Neutrophil Recruitment to the Skin on the Pathology Induced by Leishmania Infection.

Leishmania (L.) are obligate intracellular protozoan parasites that cause the leishmaniases, a spectrum of neglected infectious vector-borne diseases with a broad range of clinical manifestations ranging from local cutaneous, to visceral forms of the diseases. The parasites are deposited in the mammalian skin during the blood meal of an infected female phlebotomine sand fly. The skin is a complex organ acting as the first line of physical and immune defense against pathogens. Insults to skin integrity, such as that occurring during insect feeding, induces the local secretion of pro-inflammatory molecules generating the rapid recruitment of neutrophils. At the site of infection, skin keratinocytes play a first role in host defense contributing to the recruitment of inflammatory cells to the infected dermis, of which neutrophils are the first recruited cells. Although neutrophils efficiently kill various pathogens including Leishmania, several Leishmania species have developed mechanisms to survive in these cells. In addition, through their rapid release of cytokines, neutrophils modulate the skin microenvironment at the site of infection, a process shaping the subsequent development of the adaptive immune response. Neutrophils may also be recruited later on in unhealing forms of cutaneous leishmaniasis and to the spleen and liver in visceral forms of the disease. Here, we will review the mechanisms involved in neutrophil recruitment to the skin following Leishmania infection focusing on the role of keratinocytes in this process. We will also discuss the distinct involvement of neutrophils in the outcome of leishmaniasis.

Molecular characterization of Neospora caninum MAG1, a dense granule protein secreted into the parasitophorous vacuole, and associated with the cyst wall and the cyst matrix.

SUMMARY: In Neospora caninum and Toxoplasma gondii, the parasitophorous vacuole (PV) is synthesized at the time of infection. During tachyzoite-to-bradyzoite stage conversion, the PV is later transformed into a tissue cyst that allows parasites to survive in their host for extended periods of time. We report on the characterization of NcMAG1, the N. caninum orthologue of T. gondii MAG1 (matrix antigen 1; TgMAG1). The 456 amino acid predicted NcMAG1 protein is 54% identical to TgMAG1. By immunoblotting, a rabbit antiserum raised against recombinant NcMAG1 detected a major product of approximately 67 kDa in extracts of N. caninum tachyzoite-infected Vero cells, which was stained more prominently in extracts of infected Vero cells treated to induce in vitro bradyzoite conversion. Immunofluorescence and TEM localized the protein mainly within the cyst wall and the cyst matrix. In both tachyzoites and bradyzoites, NcMAG1 was associated with the parasite dense granules. Comparison between NcMAG1 and TgMAG1 amino acid sequences revealed that the C-terminal conserved regions exhibit 66% identity, while the N-terminal variable regions exhibit only 32% identity. Antibodies against NcMAG1-conserved region cross-reacted with the orthologuous protein in T. gondii but those against the variable region did not. This indicates that the variable region possesses unique antigenic characteristics.

[Leishmaniasis and rheumatoid nodulosis in a patient with HIV infection]. / Leishmaniasis y nodulosis reumatoide en paciente con infección por el virus de la inmunodeficiencia humana.

We describe the case of a 44-year-old homosexual man diagnosed with HIV infection and visceral leishmaniasis. He presented nodules on the dorsum of the hands. Histological study of one of the nodules revealed necrobiotic palisading granulomas with abundant Leishmania amastigotes within the histiocytes and in the adjacent extracellular space. Tissue and peripheral blood cultures were positive for Leishmania infantum, zymodeme MON-24. A biopsy of healthy skin did not reveal the presence of Leishmania. A diagnosis of rheumatoid nodulosis with Leishmania was made and treatment was started with intravenous liposomal amphotericin, leading to slight improvement. We believe that the presence of the parasite within the nodules was the result of its dissemination during visceral leishmaniasis in an immunocompromised patient with HIV infection, and that the Leishmania did not have an etiological role in the appearance of the nodules. We present the first case of the association between Leishmania and rheumatoid nodulosis.

Differential Activation of Human Keratinocytes by Leishmania Species Causing Localized or Disseminated Disease.

All Leishmania species parasites are introduced into mammalian skin through a sand fly bite, but different species cause distinct clinical outcomes. Mouse studies suggest that early responses are critical determinants of subsequent adaptive immunity in leishmaniasis, yet few studies address the role of keratinocytes, the most abundant cell in the epidermis. We hypothesized that Leishmania infection causes keratinocytes to produce immunomodulatory factors that influence the outcome of infection. Incubation of primary or immortalized human keratinocytes with Leishmania infantum or Leishmania major, which cause visceral or cutaneous leishmaniasis, respectively, elicited dramatically different responses. Keratinocytes incubated with L. infantum significantly increased expression of proinflammatory genes for IL-6, IL-8, tumor necrosis factor, and IL-1B, whereas keratinocytes exposed to several L. major isolates did not. Furthermore, keratinocyte-monocyte co-incubation studies across a 4 µM semipermeable membrane suggested that L. infantum-exposed keratinocytes release soluble factors that enhance monocyte control of intracellular L. infantum replication (P < 0.01). L. major-exposed keratinocytes had no comparable effect. These data suggest that L. infantum and L. major differentially activate keratinocytes to release factors that limit infection in monocytes. We propose that keratinocytes initiate or withhold a proinflammatory response at the site of infection, generating a microenvironment uniquely tailored to each Leishmania species that may affect the course of disease.

Topical amphotericin B in ultradeformable liposomes: Formulation, skin penetration study, antifungal and antileishmanial activity in vitro.

Aiming to improve the topical delivery of AmB to treat cutaneous fungal infections and leishmaniasis, ultradeformable liposomes containing amphotericin B (AmB-UDL) were prepared, and structural and functional characterized. The effect of different edge activators, phospholipid and AmB concentration, and phospholipid to edge activator ratio on liposomal deformability, as well as on AmB liposomal content, was tested. Liposomes having Tween 80 as edge activator resulted of maximal deformability and AmB/phospholipid ratio. These consisted of AmB-UDL of 107±8nm diameter, 0.078-polydispersity index and -3±0.2mV Z potential, exhibiting monomeric AmB encapsulated in the bilayer at a 75% encapsulation efficiency. After its cytotoxicity on keratinocytes (HaCaT cells) and macrophages (J774 cells) was determined, the in vitro antifungal activity of AmB-UDL was assayed. It was found that fungal strains (albicans and non-albicans Candida ATCC strains and clinical isolates of C. albicans) were more sensitive to AmB-UDL than mammal cells. Minimum inhibitory concentration values for AmB-UDL were 5-24 and 24-50 times lower than IC50 for J774 and HaCaT cells, respectively. AmB-UDL at 1.25µg/ml also displayed 100 and 75% anti- Leishmania braziliensis promastigote and amastigote activity, respectively. Finally, upon 1h of non-occlusive incubation, the total accumulation of AmB in human skin was 40 times higher when applied as AmB-UDL than as AmBisome. AmB-UDL provided a profound AmB penetration toward deep epithelial layers, achieved without classical permeation enhancers. Because of that, topical treatments of cutaneous fungal infection and leishmaniasis with AmB-UDL may be regarded of potential of clinical significance.

Exogenous nitric oxide triggers Neospora caninum tachyzoite-to-bradyzoite stage conversion in murine epidermal keratinocyte cell cultures.

Neospora caninum, like Toxoplasma gondii, undergoes stage conversion in chronically infected animals, and forms tissue cysts which contain the slowly proliferating bradyzoite stage. These tissue cysts are delineated by a cyst wall, protect the parasite from physiological and immunological reactions on part of the host, and bradyzoites remain viable within an infected host for many years. However, unlike T. gondii, N. caninum bradyzoites have been difficult to obtain using in vitro culture techniques, and current protocols, based on those developed for T. gondii, have been shown to be not very efficient in promoting tachyzoite-to-bradyzoite stage conversion. We report here an alternative in vitro culture method to obtain stage conversion of N. caninum from the proliferative to the cystic stage by using the Nc-Liverpool isolate, murine epidermal keratinocytes as host cells, and continuous treatment of infected cultures with 70 microM sodium nitroprusside for up to 8 days. This treatment significantly reduced parasite proliferation as assessed by Neospora-specific quantitative real-time PCR. The expression of bradyzoite markers was analysed by immunofluorescence following 4 and 8 days of in vitro culture using antibodies directed against bradyzoite antigen 1, the mAbCC2, and the lectin Dolichos biflorus agglutinin. Expression of the tachyzoite-specific immunodominant antigen NcSAG1 and the tachyzoite antigen NcMIC1 was also assessed. Transmission electron microscopy revealed that the majority of parasitophorous vacuoles were in the process of forming a distinct cyst wall through accumulation of granular material at the periphery of the vacuole, and parasites exhibited the typical features of bradyzoites. These findings demonstrate the usefulness of this culture technique as a promising way to study tachyzoite-to-bradyzoite stage conversion in N. caninum in vitro.

Modulation of cytokine expression in human keratinocytes and fibroblasts by extracts of scabies mites.

Sarcoptes scabiei lives in the stratum corneum of its mammalian host. Keratinocytes and fibroblasts are among the first cells to encounter the burrowing mite and its products. The aim of this study was to determine if molecules in an extract of S. scabiei modulate the expression of cytokines by keratinocytes and fibroblasts. Human keratinocytes and fibroblasts were exposed to an extract of S. scabiei var. canis in the absence or presence of Escherichia coli lipopolysaccharide. Cytokine expression was measured by an enzyme-linked immunosorbent assay. Components in the S. scabiei extract induced marked increases in secretion of interleukin-6 (IL-6) and vascular endothelial growth factor (VEGF) and slight increases in production of granulocyte-colony-stimulating factor (G-CSF) by keratinocytes. The scabies extract down-regulated keratinocyte secretion of IL-1 receptor antagonist, but did not influence the production of IL-1alpha or IL-1beta. In comparison, components in the scabies extract induced marked increases in the elaboration of IL-6, IL-8, G-CSF, and VEGF by fibroblasts. Neither cell type produced eotaxin, stem cell factor, or tumor necrosis factor-alpha under any of the conditions tested. This study demonstrates that components in an extract of the mite S. scabiei are able to influence cytokine expression by human keratinocytes and fibroblasts.

Penetration of Schistosoma mansoni cercariae into a living skin equivalent.

We evaluated the use of a living skin equivalent (LSE) as a suitable membrane for Schistosoma mansoni cercarial penetration. LSE is a living artificial skin composed of a dermal layer containing human dermal fibroblasts embedded in a collagen lattice and an epidermal layer consisting of differentiated human keratinocytes. The keratinocytes differentiate into a stratum corneumlike layer, whereas the dermal-epidermal junction forms a layer similar, but not identical to, the basement membrane. We exposed LSE to 50 cercariae for 0, 3, 6, 20, and 30 hr at 37 C, and the percentage of penetration was evaluated by counting cercariae remaining on the LSE surface. No cercarial penetration was observed in the first 15 min of exposure; however, penetration was detected at all other times. Maximum penetration rates were observed at 20 hr (80%). In other experiments LSE was pretreated topically with 0 or 4 micrograms/cm2 linoleic acid, then exposed to between 800 and 1,000 cercariae for 18-20 hr at 37 C. LSE pretreated with linoleate had significantly higher penetration rates than untreated membranes (81% +/- 2.51% vs. 65.9% +/- 6.97%, P = 0.03). Increasing linoleate concentrations from 10 to 40 micrograms/cm2 gradually decreased the ability of cercariae to penetrate the membrane. Some LSE membranes also were processed for light microscopy, and we present photomicrographs showing schistosomulae within the epidermal and dermal layers of the LSE. We conclude that despite the time it takes for cercariae to penetrate LSE, these membranes may allow investigators to examine, in vitro, host-parasite interactions at the level of the skin.

Cytopathogenicity of clinical and environmental Acanthamoeba isolates for two mammalian cell lines.

The cytopathic effect (CPE) of southern African, British, and an Asian strain of Acanthamoeba was assessed using a system developed around 2 different mammalian cell (MC) lines. The time taken by the amebae to destroy cell cultures completely was shown to be dependent largely on the size of the amebic inoculum and the cell type. This highlights the need to assess carefully the behavior of cell lines prior to using them for cytopathic testing. Assays performed with conditioned medium collected from both MCs and amebic cells indicated that mechanical destruction may have been primarily responsible for the CPE. Furthermore, not all strains of Acanthamoeba lose cytopathogenicity after being passaged in axenic culture for extended periods. The use of MC cultures was shown to be an accurate, rapid, and repeatable means of assaying the CPE of strains of Acanthamoeba.

Production of IL-1 alpha and IL-1 beta by human skin equivalents parasitized by Sarcoptes scabiei.

Human skin equivalents (HSEs) were used as a model to investigate interleukin (IL)-1 alpha and IL-1 beta secretions by keratinocytes stimulated by Sarcoptes scabiei (SS). SS mites burrowed into the stratum corneum when placed on the surface of cultured HSEs. Mites lived for 14 days. Mites and mite products induced cells in the HSEs to secrete IL-1 alpha and IL-1 beta within 16 hr. Scabies mites induced production of greater amounts of IL-1 alpha than IL-1 beta. Hepatocyte growth factor in the culture medium at 3 and 30 ng/ml upregulated the secretions of both IL-1 alpha and IL-1 beta by mite-infested skin equivalents, whereas 10 ng/ml of IL-6 upregulated production of only IL-1 beta. Therefore, these cytokines were important immunomodulating factors influencing keratinocyte secretion of IL-1 alpha and IL-1 beta in vitro. The results of this study provide the first evidence that keratinocytes (possibly fibroblasts) in the skin produce these cytokines in response to scabies mites or other ectoparasitic arthropods. Because IL-1 alpha and IL-1 beta are potent inducers of inflammation and keratinocytes are among the first effector cells to encounter scabies mites and their products, these cells may be key initiators of the inflammatory/immune reaction to scabies.

Detection of Leishmania infantum kinetoplast minicircle DNA by Real Time PCR in hair of dogs with leishmaniosis.

It is known that hair can accumulate environmental toxics and excrete foreign chemical or biological substances. In this context, we hypothesized that foreign DNA could be found in the hair of an infected organism, and thus, be detected by Real Time PCR in the hair of Leishmania infantum naturally infected dogs. A population of 28 dogs living in Leishmania endemic areas was divided into two groups: A (13 Leishmania infected dogs) and B (15 healthy dogs). Blood, lymph node and ear hair samples from all of them were tested for the presence of parasite kinetoplast DNA (kDNA). For the same purpose, hair of several body areas and hair sections of two infected dogs were also analyzed. Epidermal keratinocytes from an infected animal were also analyzed for reactivity against Leishmania antigens by ELISA and for the presence of kDNA. Regarding to dogs from group A, parasite kDNA was detected in the 100% of lymph node samples. The sensitivity of Real Time PCR in ear hair was similar to that obtained in blood (9 positive out of 13 versus 8 positive out of 13, respectively). Moreover, the presence of L. infantum kDNA was also detected in the hair of all the analyzed body zones, in all hair sections and in epidermal keratinocytes. In infected dogs, parasite kDNA could be detected and quantified from just one single hair, whereas it was not detected in any of the samples of the healthy dogs. This work describes a new method for a reliable and non-invasive diagnosis of canine leishmaniosis using hair samples of infected animals. The data presented also provide some insights for the understanding of the physiology of keratinocytes and the role of hair as a specialized tissue in the kidnapping and removal of foreign DNA.

FasL and TRAIL induce epidermal apoptosis and skin ulceration upon exposure to Leishmania major.

Receptor-mediated apoptosis is proposed as an important regulator of keratinocyte homeostasis in human epidermis. We have previously reported that Fas/FasL interactions in epidermis are altered during cutaneous leishmaniasis (CL) and that keratinocyte death through apoptosis may play a pathogenic role for skin ulceration. To further investigate the alterations of apoptosis during CL, a keratinocyte cell line (HaCaT) and primary human epidermal keratinocytes were incubated with supernatants from Leishmania major-infected peripheral blood mononuclear cells. An apoptosis-specific microarray was used to assess mRNA expression in HaCaT cells exposed to supernatants derived from L. major-infected cultures. Fas and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) mRNA and protein expression were significantly up-regulated, and apoptosis was detected in both HaCaT and human epidermal keratinocyte cells. The keratinocyte apoptosis was partly inhibited through blocking of Fas or FasL and even more efficiently through TRAIL neutralization. Up-regulation of Fas on keratinocytes in epidermis and the presence of FasL-expressing macrophages and T cells in dermis were previously reported by us. In this study, keratinocytes expressing TRAIL, as well as the proapoptotic receptor TRAIL-R2, were detected in skin biopsies from CL cases. We propose that activation of Fas and TRAIL apoptosis pathways, in the presence of inflammatory mediators at the site of infection, leads to tissue destruction and ulceration during CL.

Delayed tail loss during the invasion of human skin by schistosome cercariae.

Schistosomiasis is initiated when cercarial larvae invade human skin. Contrary to long-held assumptions, most cercariae of Schistosoma mansoni do not shed their propulsive tails as they penetrate. Scanning electron microscopy studies and infection experiments with entire human skin and differentiated, stratum corneum-like, human keratinocyte cultures, have shown that most cercarial tails enter the skin along with their bodies. We propose that this behaviour is an adaptive trait linked with concomitant immunity.