Matrix remodelling and fibroblast phenotype in early lesions of human cutaneous leishmaniasis

The immunomicrotope of Leishmania control and persistence

Leishmania is an intracellular protozoan transmitted by sand fly vectors; it causes cutaneous, mucocutaneous, or visceral disease. Its growth and survival are impeded by type 1 T helper cell responses, which entail interferon (IFN)-γ-mediated macrophage activation. Leishmania partially escapes this host defense by triggering immune cell and cytokine responses that favor parasite replication rather than killing. Novel methods for in situ analyses have revealed that the pathways of immune control and microbial evasion are strongly influenced by the tissue context, the micro milieu factors, and the metabolism at the site of infection, which we collectively term the 'immunomicrotope'. Understanding the components and the impact of the immunomicrotope will enable the development of novel strategies for the treatment of chronic leishmaniasis.

Dual Role of Insulin-Like Growth Factor (IGF)-I in American Tegumentary Leishmaniasis

Background

Cytokines and growth factors involved in the tissue inflammatory process influence the outcome of Leishmania infection. Insulin-like growth factor (IGF-I) constitutively present in the skin may participate in the inflammatory process and parasite-host interaction. Previous work has shown that preincubation of Leishmania (Leishmania) amazonensis with recombinant IGF-I induces accelerated lesion development. However, in human cutaneous leishmaniasis (CL) pathogenesis, it is more relevant to the persistent inflammatory process than progressive parasite proliferation. In this context, we aimed to investigate whether IGF-I was present in the CL lesions and if this factor may influence the lesions' development acting on parasite growth and/or on the inflammatory/healing process. Methodology. Fifty-one CL patients' skin lesion samples from endemic area of L. (Viannia) braziliensis infection were submitted to histopathological analysis and searched for Leishmania and IGF-I expression by immunohistochemistry.

Results

In human CL lesions, IGF-I was observed preferentially in the late lesion (more than 90 days), and the percentage of positive area for IGF-I was positively correlated with duration of illness (r = 0.42, P < 0.05). IGF-I was highly expressed in the inflammatory infiltrate of CL lesions from patients evolving with good response to therapy (2.8% ± 2.1%; median = 2.1%; n = 18) than poor responders (1.3% ± 1.1%; median: 1.05%; n = 6; P < 0.05).

Conclusions

It is the first time that IGF-I was detected in lesions of infectious cutaneous disease, specifically in American tegumentary leishmaniasis. IGF-I was related to chronicity and good response to treatment. We may relate this finding to the efficient anti-inflammatory response and the known action of IGF-I in wound repair. The present data highlight the importance of searching nonspecific factors besides adaptive immune elements in the study of leishmaniasis' pathogenesis.

T cells specific to leishmania and other nonrelated microbial antigens can migrate to human leishmaniasis skin lesions

Immunopathological studies have contributed to the characterization of in situ inflammatory infiltrates in cutaneous leishmaniasis (CL). However, little is known about the T-cell antigen reactivity of these lesions. Our objective was to analyze the responsiveness of lymphocytes from CL lesions to leishmanial and nonrelated antigens in terms of proliferation and the production of cytokines. Mononuclear cells were extracted from lesions, and blood from CL patients infected with Leishmania (Viannia) braziliensis. Activated cells accounted for 35-45% of lesions T-cell subsets. Elevated levels of C1.7/CD244(+)CD8(+) T cells suggest in situ cytotoxic effector function. Lymphocytes isolated from the leishmaniasis lesions proliferated and produced IFN-gamma in response to leishmanial antigens as well as to irrelevant antigens such as Toxoplasma gondii (Tg). Patients presenting with larger lesions had the highest lymphocyte proliferation indexes. A high frequency of Tg-specific cells was detected in the lesions by limiting dilution assay, similar to the frequency of Leishmania-specific cells. Importantly, Tg-reactive cells were not found in lesions of patients without a history of toxoplasmosis. The proportion of Leishmania-reactive CD4(+) and CD8(+) T cells in the lesions was quite variable. Overall, these data suggest that T cells reactive to nonrelevant antigens can migrate to leishmanial lesions and possibly influence the pathogenesis of the disease.

Flow cytometric analysis of cellular infiltrate from American tegumentary leishmaniasis lesions

BACKGROUND

CD4+ and CD8+ T lymphocytes play different roles in the outcome of leishmaniasis. However, T-cell distribution in lesions shows significant variability in in situ immunocytochemical studies.

OBJECTIVES

In this report flow cytometry was used to determine the predominant T-cell subsets in leishmaniasis lesions, and their relationship with Leishmania-responsive circulating T cells.

PATIENTS AND METHODS

Mononuclear cells from lesions or peripheral blood (PBMC) of 34 cutaneous (CL), four mucosal (ML) and four disseminated leishmaniasis were phenotypically characterized by flow cytometry. Leishmania-responsive T cells were obtained after in vitro stimulation of PBMC with leishmanial antigens.

RESULTS/CONCLUSIONS

Variable amounts of gammadelta lymphocytes were present in all lesions, with no association with duration of illness. The highest percentages of interleukin-2R- and interferon-gammaR-positive cells were observed in ML lesions and could render these T cells more susceptible to the effects of these cytokines. The distribution of intralesional T-lymphocyte subsets was quite variable (CD4+ > CD8+ = 18 cases, CD8+ > CD4+ = 12 cases and CD4+ congruent with CD8+ = 4 cases) without any association with clinical parameters, and could explain the controversy regarding proportions of these T-cell subsets in leishmaniasis lesions. Low percentages of Leishmania-reactive CD8+ T cells were observed in blood while an enrichment of CD8+ cells was shown in the inflammatory infiltrate, suggesting that local immunoregulatory factors could favour the recruitment and/or proliferation of local CD8+ lymphocytes. Increased percentages of CD8+ cells observed in older lesions are consistent with the hypothesis that they can mediate healing, although their involvement in tissue damage cannot be ruled out. It is possible that these mechanisms can influence the clinical outcome or even the response to therapy.

The wound repair response controls outcome to cutaneous leishmaniasis

Chronic microbial infections are associated with fibrotic and inflammatory reactions known as granulomas showing similarities to wound-healing and tissue repair processes. We have previously mapped three leishmaniasis susceptibility loci, designated lmr1, -2, and -3, which exert their effect independently of T cell immune responses. Here, we show that the wound repair response is critically important for the rapid cure in murine cutaneous leishmaniasis caused by Leishmania major. Mice congenic for leishmaniasis resistance loci, which cured their lesions more rapidly than their susceptible parents, also expressed differentially genes involved in tissue repair, laid down more ordered collagen fibers, and healed punch biopsy wounds more rapidly. Fibroblast monolayers from these mice repaired in vitro wounds faster, and this process was accelerated by supernatants from infected macrophages. Because these effects are independent of T cell-mediated immunity, we conclude that the rate of wound healing is likely to be an important component of innate immunity involved in resistance to cutaneous leishmaniasis.

Leishmania-host-cell interaction: complexities and alternative views

Leishmania are protozoan parasites that infect various mammalian species, including humans. It is generally thought that random attachment of the flagellated promastigotes to mononuclear phagocytes initiates their uptake via circumferential pseudopods. Intracellularly, the promastigotes become located in phagolysosomes in which they transform to and survive as 'aflagellated' amastigotes that hide their shortened flagellum within the flagellar pocket. Unrestricted replication of these amastigotes is assumed to cause the eventual burst of the host cell, thereby releasing the infectious parasites. Here, Mike Rittig and Christian Bogdan review a large body of literature containing potentially important but poorly appreciated findings, which together with recent results, argue for Leishmania-host-cell interactions that are much more complex than generally thought.

Fibroblasts as host cells in latent leishmaniosis

Intracellular parasites are known to persist lifelong in mammalian hosts after the clinical cure of the disease, but the mechanisms of persistence are poorly understood. Here, we show by confocal laser microscopy that in the draining lymph nodes of mice that had healed a cutaneous infection with Leishmania major, 40% of the persisting parasites were associated with fibroblasts forming the reticular meshwork of the lymph nodes. In vitro, both promastigotes and amastigotes of L. major infected primary skin or lymph node fibroblasts. Compared with macrophages, cytokine-activated fibroblasts had a reduced ability to express type 2 nitric oxide synthase and to kill intracellular L. major. These data identify fibroblasts as an important host cell for Leishmania during the chronic phase of infection and suggest that they might serve as safe targets for the parasites in clinically latent disease.

Interferon-gamma, an anti-fibrogenic cytokine which binds to heparan sulfate

Interferon-gamma is a T cell secreted cytokine. It has a great number of biological activities, among which is the down regulation of collagen molecules. IFN-gamma acts through cell surface receptors, but also binds to heparan sulfate proteoglycans. In vivo, it is postulated that the heparan sulfate/IFN-gamma interaction can modulate the activity and availability of the cytokine.

Cell-matrix patterns in the cutaneous lesion of chromomycosis

Chromomycosis is a chronic fungal infection characterized by dermal fibrosis with persisting fungi in situ, generally leading to a verrucous skin lesion. The absence of good clinical results under specific treatment suggests irreversibility of the fibrotic lesion. Frozen and paraffin-embedded skin biopsies of eleven patients with chromomycosis due to Phialophora pedrosoi were studied by immunohistochemistry and electron microscopy. Distinct cell-matrix patterns were found in different tissue localizations: neutrophilic abscesses with oedema and necrotic keratinocytes in the epidermis; dense connective matrix around inflammatory infiltrates, mainly composed of macrophages and giant cells, and organized granuloma in the dermis. Active fibroblasts and mast cells were constantly observed. The inability of fibrotic tissue to be remodelled seems correlated to the nature and the organization of the matrix components but, the factors triggering the initial fibrogenic events remain to be characterized.

Cell populations in the lesion of human cutaneous leishmaniasis: a light microscopical, immunohistochemical and ultrastructural study

To characterize the in situ cellular immune response in localized cutaneous leishmaniasis (LCL), the authors studied frozen skin biopsies from 50 patients with LCL due to Leishmania braziliensis guyanensis. A panel of 31 monoclonal antibodies was used, which defined the number and distribution of inflammatory cell subsets. Skin inflammatory infiltrates were composed of T cells (with a local CD4/CD8 ratio of 1.05 +/- 0.7 vs 1.48 +/- 0.3 in peripheral blood), macrophages and a smaller number of B cells, natural killer cells and granulocytes. Most of the T cells expressed activation markers (interleukin-2 and transferrin receptors, HLA-DR+) and an increase in T-cell-receptor gamma delta expression was noted. Analysis of the CD4+ subpopulations with newly available reagents showed that helper T cells (CD4+CD45RO+) exceeded the suppressor/inducer subset (CD4+CD45RA+) by 1.4:1. There were no differences between local immune variables from patients with primary infection (45 patients) and those with recurrence (5). In 7 patients, biopsies were analysed before and 1 month after specific treatment, and did not show significant differences except for a small increase of dermal CD1a+ (Langerhans) cells/mm2. The observed pattern of cellular skin infiltration suggests an immune-mediated tissue injury including T-cell-mediated cytotoxicity and delayed hypersensitivity reactions in addition to direct parasitic action.