Cell-mediated immune responses in mice infected with Fonsecaea pedrosoi

Immune Sensing and Potential Immunotherapeutic Approaches to Control Chromoblastomycosis

Chromoblastomycosis (CBM) is a neglected, chronic, and progressive subcutaneous mycosis caused by different species of fungi from the Herpotrichiellaceae family. CBM disease is usually associated with agricultural activities, and its infection is characterized by verrucous, erythematous papules, and atrophic lesions on the upper and lower limbs, leading to social stigma and impacts on patients' welfare. The economic aspect of disease treatment is another relevant issue. There is no specific treatment for CBM, and different anti-fungal drug associations are used to treat the patients. However, the long period of the disease and the high cost of the treatment lead to treatment interruption and, consequently, relapse of the disease. In previous years, great progress had been made in the comprehension of the CBM pathophysiology. In this review, we discuss the differences in the cell wall composition of conidia, hyphae, and muriform cells, with a particular focus on the activation of the host immune response. We also highlight the importance of studies about the host skin immunology in CBM. Finally, we explore different immunotherapeutic studies, highlighting the importance of these approaches for future treatment strategies for CBM.

Chromoblastomycosis

Chromoblastomycosis (CBM), also known as chromomycosis, is one of the most prevalent implantation fungal infections, being the most common of the gamut of mycoses caused by melanized or brown-pigmented fungi. CBM is mainly a tropical or subtropical disease that may affect individuals with certain risk factors around the world. The following characteristics are associated with this disease: (i) traumatic inoculation by implantation from an environmental source, leading to an initial cutaneous lesion at the inoculation site; (ii) chronic and progressive cutaneous and subcutaneous tissular involvement associated with fibrotic and granulomatous reactions associated with microabscesses and often with tissue proliferation; (iii) a nonprotective T helper type 2 (Th2) immune response with ineffective humoral involvement; and (iv) the presence of muriform (sclerotic) cells embedded in the affected tissue. CBM lesions are clinically polymorphic and are commonly misdiagnosed as various other infectious and noninfectious diseases. In its more severe clinical forms, CBM may cause an incapacity for labor due to fibrotic sequelae and also due to a series of clinical complications, and if not recognized at an early stage, this disease can be refractory to antifungal therapy.

Black yeasts and their filamentous relatives: principles of pathogenesis and host defense

Among the melanized fungi, the so-called "black yeasts" and their filamentous relatives are particularly significant as agents of severe phaeohyphomycosis, chromoblastomycosis, and mycetoma in humans and animals. The pathogenicity and virulence of these fungi may differ significantly between closely related species. The factors which probably are of significance for pathogenicity include the presence of melanin and carotene, formation of thick cell walls and meristematic growth, presence of yeast-like phases, thermo- and perhaps also osmotolerance, adhesion, hydrophobicity, assimilation of aromatic hydrocarbons, and production of siderophores. Host defense has been shown to rely mainly on the ingestion and elimination of fungal cells by cells of the innate immune system, especially neutrophils and macrophages. However, there is increasing evidence supporting a role of T-cell-mediated immune responses, with increased interleukin-10 (IL-10) and low levels of gamma interferon (IFN-γ) being deleterious during the infection. There are no standardized therapies for treatment. It is therefore important to obtain in vitro susceptibilities of individual patients' fungal isolates in order to provide useful information for selection of appropriate treatment protocols. This article discusses the pathogenesis and host defense factors for these fungi and their severity, chronicity, and subsequent impact on treatment and prevention of diseases in human or animal hosts.

Revisiting the clinical and histopathological aspects of patients with chromoblastomycosis from the Brazilian Amazon region

BACKGROUND AND AIMS

Chromoblastomycosis is a chronic fungal infection caused by species of the family Dematiaceae. Fonsecaea pedrosoi is the most common etiological agent. The objective of this study was to describe the epidemiological and mycological profile of patients with chromoblastomycosis from the Amazon region of Brazil and to correlate the clinical forms with the histopathological findings and severity criteria.

METHODS

Sixty-five patients were submitted to mycological (direct, culture, and microculture) and histopathological (hematoxylin-eosin staining) examination. Severity of the disease was classified according to the criteria proposed by Carrión in 1950.

RESULTS

Most patients were males (93.8%) and laborers (89.2%). There was a predominance of verrucous lesions (55.4%), which were mainly found on the lower limbs (81.5%). Two major types of tissue reaction were observed: a granulomatous reaction characterized by the formation of suppurative granulomas rich in fungal cells, which were almost always seen in verrucous lesions, and a reaction characterized by the formation of tuberculoid granulomas with few parasites, which were mainly found in well-delimited erythematous plaque-like and cicatricial lesions (p = 0.0001). A peculiar type of organized mycotic granuloma was observed in 20 subjects. Suppurative granulomas were more frequently detected in severe lesions (p = 0.0189) and in lesions with a duration of >10 years (p = 0.0408).

CONCLUSIONS

These results suggest that verrucous lesions present a less competent inflammatory tissue response than patients who develop a well-formed tuberculoid reaction. The latter is associated with a more effective immune response as observed in the limited clinical forms of chromoblastomycosis.

Local phagocytic responses after murine infection with different forms of Fonsecaea pedrosoi and sclerotic bodies originating from an inoculum of conidiogenous cells

Fonsecaea pedrosoi is an important causative agent of chromoblastomycosis (CBM) especially in humid areas of the world; however, little is known about the infective forms of this agent that cause CBM. The aim of this study was to investigate the murine tissue response to inoculation with different forms of F. pedrosoi and the morphological changes of the fungal cells in vivo. BALB/c mice were inoculated intraperitoneally with hyphae, conidia or conidiogenous cells and conidia (CCC) at a single site. In addition, the abdomen and footpads were infected subcutaneously with CCC. Fungal forms were inoculated at a final concentration of 1 × 10(6) cells. Hyphae and ungerminated conidia inocula could not be transformed into parasitic forms. In tissue, a great number of conidiogenous cells underwent transformation into sclerotic bodies, which were more resistant to phagocytes in vivo than conidia and hyphae. Clinical and mycological cure of animals infected with CCC was observed from the fourth to the sixth week of infection, while conidia and hyphae infections were faster and generally lasted 2 to 3 weeks. A high number of destructed conidia was observed intracellularly in macrophages. The migration of neutrophils to the inflammatory site seems important for microbicidal activity, particularly against hyphae. Our observations suggest that inocula with conidiogenous cells are associated with in vivo transformation into sclerotic bodies and that local immune response involved with host resistance to experimental F. pedrosoi-infection is primarily mediated by neutrophils as observed in histological sections.

Prolonged infection by Fonsecaea pedrosoi after antigenic co-stimulation at different sites in experimental murine chromoblastomycosis

In the present study, we examined prolonged infection after antigenic co-stimulation by inoculation of the fungus Fonsecaea pedrosoi at two different sites in three mouse strains (BALB/c, Swiss, and C57BL/6). Using this murine model of infection, we showed that antigen induction of infection at more than one site led to a local suppression of active lesions, which increased the time course of experimental chromoblastomycosis (CBM). Footpad infection with a simultaneous infection of the peritoneum or a mucosal site appeared to cause prolonged infection and frequent fungal disseminations. Using knockout (KO) mice, we observed that antigenic co-stimulation caused progressive illness in CD8-KO animals and an effective immune response in the absence of IL-10. In Xid mice, co-stimulation provoked chronic infection (not prolonged), suggesting that B1 B cells play an important role in the control of fungal infection. The tissue response to infection was similar in all co-stimulated mouse groups, as anatomopathologic sections revealed multifocal lesions (granuloma-like). In general, these mice had acute responses at primary antigenic sites with an intense migration of polymorphonuclear leukocytes (PMNs), whereas the distant infection sites (footpad) showed signs of chronic infection. The migration of PMNs to the secondary site (footpad) increased in the later periods of infection, especially after the disappearance of the primary antigenic focus. PMN migration was associated with lesion-dormancy breakage and fungal elimination. Our findings suggest that the host inflammatory/suppression mechanisms induced by antigenic co-stimulation to systemically fight the same pathogen act coordinately through responses that differ at the sites of infection between acute and chronic integrated healing processes that are more prolonged than an acute infection at a single site. However, the long persistence of fungal cells in the host may be linked to microbial adaptation to a parasitic infection as observed in co-stimulated Xid mice.

Fungal x host interactions in Chromoblastomycosis: what we have learned from animal models and what is yet to be solved

Animal studies with chromoblastomycosis were initiated together with the first descriptions of the disease. In this editorial commentary, animal models are briefly reviewed, and the available data based on new immunology tools are discussed.

Detection of delayed hypersensitivity to Fonsecaea pedrosoi metabolic antigen (chromomycin)

An experimental study was conducted between January 2002 and April 2003 for the detection of delayed hypersensitivity to Fonsecaea pedrosoi metabolic antigen (chromomycin) in skin tests. A total of 194 subjects were attended by spontaneous demand at the Infectious and Parasitic Diseases outpatient clinic of the Federal University of Maranhão-UFMA and at the Department of Microbiology, Federal University of Minas Gerais-UFMG and classified into three groups: patients with chromoblastomycosis caused by F. pedrosoi (n=20), healthy subjects (n=86) and patients with other diseases (n=88). For the skin test, 0.1 ml of the antigen was applied to the anterior side of the right forearm and 0.1 ml Smith medium was applied to the anterior side of the left forearm as control. The results were analyzed 48 h after inoculation of the antigen and an induration >/= 5 mm was considered to indicate a positive test. A cellular immune response to chromomycin was detected in 18 (90.0%) of the 20 patients with chromoblastomycosis caused by F. pedrosoi, and one of the patients with a negative test had reactional leprosy. Eighty-five (98.8%) of the 86 healthy subjects presented a negative reaction and only one reacted positively to the antigen. The skin test was negative in all 88 (100%) patients with other diseases, such as dermatophytosis, paracoccidioidomycosis, pulmonary aspergilloma, candidiasis, pityriasis versicolor, tuberculosis, leprosy, tegumentary leishmaniasis and syphilis, and one case of chromoblastomycosis caused by Rhinocladiella aquaspersa. Chromomycin was effective in detecting delayed hypersensitivity in patients with chromoblastomycosis caused by F. pedrosoi, with a sensitivity and specificity of 90.0% and 98.8%, respectively. These results suggest that this antigen can be used in the auxiliary diagnosis of the disease and also in epidemiological studies for determination of the prevalence of chromoblastomycosis infection in endemic areas.

Absence of CD4+ T cells impairs host defence of mice infected with Fonsecaea pedrosoi

Chromoblastomycosis is a human chronic, often debilitating, suppurative, granulomatus mycosis of the skin and subcutaneous tissues beginning after inoculation trauma. It occurs worldwide, but is more frequently observed in tropical countries such as Brazil. Some studies have focused on fungus-host interaction, showing a predominantly cell-mediated immune response, with the activation of macrophages involved in fungus phagocytosis. Immunization with live conidia produced a high influx of CD4 T cells into the draining lymph node. The sensitized T cells proliferate in vitro when restimulated with specific antigen and preferentially produce IFN- gamma. To better characterize the role played by T cells on the chromoblastomycosis infection we used mice deficient for CD4 and CD8. Data determined by CFU counts associated with decreased DTH and IFN-gamma production of infected mice clearly demonstrated that, during experimental F. pedrosoi infection, absence of CD4(+) cells induces a more severe disease.

Molecular analysis and pathogenicity of the Cladophialophora carrionii complex, with the description of a novel species

Cladophialophora carrionii is one of the four major etiologic agents of human chromoblastomycosis in semi-arid climates. This species was studied using sequence data of the internal transcribed spacer region of rDNA, the partial beta-tubulin gene and an intron in the translation elongation factor 1-alpha gene, in addition to morphology. With all genes a clear bipartition was observed, which corresponded with minute differences in conidiophore morphology. A new species, C. yegresii, was introduced, which appeared to be, in contrast to C. carrionii, associated with living cactus plants. All strains from humans, and a few isolates from dead cactus debris, belonged to C. carrionii, for which a lectotype was designated. Artificial inoculation of cactus plants grown from seeds in the greenhouse showed that both fungi are able to persist in cactus tissue. When reaching the spines they produce cells that morphologically resemble the muriform cells known as the "invasive form" in chromoblastomycosis. The tested clinical strain of C. carrionii proved to be more virulent in cactus than the environmental strain of C. yegresii that originated from the same species of cactus, Stenocereus griseus. The muriform cell expressed in cactus spines can be regarded as the extremotolerant survival phase, and is likely to play an essential role in the natural life cycle of these organisms.

Cellular immune response of patients with chromoblastomycosis undergoing antifungal therapy

One of the most characteristic features of the chromoblastomycosis is its unresponsiveness to treatment. In order to analyzed whether during therapy could be observed a change of cellular immune response pattern, we evaluated the production of IL-10, TNF-alpha and IFN-gamma, as well as proliferation of peripheral blood mononuclear cell (PBMC) from patients in different periods of chemotherapy treatment. Our results showed that after 6 months of treatment cells from patients proliferated to fungal antigens and produced a significant level of IFN-gamma. However, after 1 year of treatment a low proliferation of T cells and production of IFN-gamma accompanied by an increase of IL-10 were observed when compared with 6 months of treatment.

Delayed-type hypersensitivity response to crude and fractionated antigens from Fonsecaea pedrosoi CMMI 1 grown in different culture media

Chromoblastomycosis is a subcutaneous fungal disease caused by dematiaceous fungi, especially by Fonsecaea pedrosoi, regarded as its major causative agent in Brazil. In recent years there has been a decline in the use of skin testing for delayed-type hypersensitivity (DTH) in epidemiological surveys of fungal infections, mainly because of the unpredictability of positive reactions and lack of specificity of the antigens used. The aim of the present study was to assess delayed-type skin tests in guinea pigs experimentally infected with F. pedrosoi using exoantigens prepared from two culture filtrates. Sixteen adult male guinea pigs were inoculated intratesticularly with fungal cells and submitted to sensitivity assays 4 weeks after inoculation. They received an intradermal injection with crude and fractionated antigens from Alviano's and Smith's cultures, and were assessed 24 and 48 h thereafter. Except for one animal, all of them had positive indurations after 48 h. There were no statistical differences between the measurements at 24 and 48 h for each exoantigen used, neither among the induration measurements at 48 h when different preparations were compared. Our results suggest that a delayed-type skin test using antigens produced in synthetic media may be useful for the assessment of primary exposure to chromoblastomycosis.

Inhibition of Nitric Oxide Production by Macrophages in Chromoblastomycosis: A Role for Fonsecaea pedrosoi Melanin

Chromoblastomycosis is a chronic and progressive deep mycosis that is usually found in tropical and subtropical areas. Fonsecaea pedrosoi is considered its most frequent etiologic agent and causes a typical granulomatous inflammatory response, whose degree reflects the immune status of the host. Since macrophages play a fundamental role in the control of the infection, this study aimed at investigating the production of oxygen reactive specimens, the phagocytic capacity and the production of nitric oxide (NO) by macrophages employing in vitro assays and an in vivo model of chromoblastomycosis. Our results demonstrated that, during the infection, peritoneal macrophages show an increased phagocytic capacity and H2O2 production, but also a reduced ability to produce NO. Moreover, F. pedrosoi stimulated H2O2 production in vitro but not the synthesis of NO. The incubation of IFNgamma and LPS-stimulated macrophages with melanin, obtained from the fungus, inhibited NO production. Examination of the liver and spleen of infected animals, at day 30 or 60 following inoculation, showed a progressive increase in the number and size of granulomas, indicating that macrophages are properly mobilized and activated. Our data suggest that the inability of the host to clear F. pedrosoi, leading to a chronic disease, is due, at least in part, to the inhibition of NO synthesis by macrophages by fungus-produced melanin.

Cytokines and lymphocyte proliferation in patients with different clinical forms of chromoblastomycosis

Chromoblastomycosis is a chronic, often debilitating, suppurative, granulomatus mycosis of the skin and subcutaneous tissues beginning after inoculation trauma. It occurs world-wide, but is more frequently observed in tropical countries such as Brazil. The disease is usually insidious, and the lesions increase slowly but progressively, not responding to the usual treatments and quite often reappearing. The host defense mechanism in chromoblastomycosis has not been extensively investigated. Some studies have focused on fungus-host interaction, showing a predominantly cellular immune response, with the activation of macrophages involved in fungus phagocytosis. Although phagocytosis did occur, death of fungal cells was rarely observed. The ability of Fonsecaea pedrosoi to produce secreted or cell wall-associated melanin-like components, protects against destruction by host immune cells in vitro. Until now, the T cell immune response in chromoblastomycosis is undefined. In the present work, it was shown that, in patients with the severe form of the disease, predominant production of IL-10 cytokine, low levels of IFN-gamma and inefficient T cell proliferation were induced. In contrast, in patients with a mild form of the disease, predominant production of IFN-gamma cytokine, low levels of IL-10 and efficient T cell proliferation were observed.

Antigen distribution and antigen-presenting cells in skin biopsies of human chromoblastomycosis

BACKGROUND

Chromoblastomycosis is a chronic, suppurative, granulomatous mycosis usually confined to skin and subcutaneous tissues. The host defense mechanisms in chromoblastomycosis have not been extensively investigated. The purpose of the present study was to determine the distribution and pathways of the fungal antigen(s) and the possible role of the different immunocompetent cells in antigen processing in skin lesions.

METHODS

The distribution of Fonsecaea pedrosoi antigen(s) in human skin was studied in 18 biopsies from 14 patients with chromoblastomycosis. A purified polyclonal immune serum raised in rabbits against metabolic antigen(s) of F. pedrosoi was used to detect yeast antigen(s) by immunohistochemical procedures. Double immunolabeling was performed with yeast antigen(s) and Langerhans' cells [labeled with anti-S100 protein monoclonal antibody (MoAb)], yeast antigen(s) and factor XIIIa+ dermal dendrocytes (immunolabeled with anti-factor XIIIa polyclonal antibody), and yeast antigen(s) and macrophages (labeled with CD 68 monoclonal antibody).

RESULTS

The F. pedrosoi antigen(s) accumulated in the skin macrophages and, in a few instances, in factor XIIIa+ dendrocytes and Langerhans' cells.

CONCLUSIONS

The data obtained suggest that chiefly macrophages, also Langerhans' cells and factor XIIIa+ dermal dendrocytes, function as antigen-presenting cells in chromoblastomycosis.

The in vitro susceptibility of Fonsecaea pedrosoi to activated macrophages

Light and electron microscopy were used to analyze in vitro the interaction of Fonsecaea pedrosoi with in vivo activated-macrophages. Adherence of the fungi to the surface of activated macrophages triggers the respiratory burst as revealed by reduction of nitroblue tetrazolium. Transmission electron microscopy revealed NAD(PO)H-oxidase activity in the portions of the macrophage plasma of membrane that were in contact with the fungus as well as within phagocytic vacuoles. Activated macrophages failed to kill ingested fungi, but they showed a fungistatic activity delaying germ tube and hyphae formation.

Chromoblastomycosis. A morphological investigation of the host-parasite interaction

Chromoblastomycosis is a distinct cutaneous mycotic infection. Histologically it is characterized by the presence of fungus invariably in the yeast phase and by macrophages in large numbers. The morphology of fungus in both yeast and hyphal phases and its interaction with mononuclear phagocytes were examined using ultrastructural techniques. The major structural difference between the fungus in cutaneous tissue and that from a culture medium was a striking increase in cell wall thickness in the former. In the skin, the organisms were phagocytised by macrophages and enclosed in large membrane limited intracytoplasmic vacuoles. The thick, stratified, electron-dense fungal cell wall was observed in stages of alteration of varying severity. Most common was a granular modification of the outermost layers of the cell wall in contact with the vacuolar content. Fragmentation, splitting and rupture of this and deeper layers was also seen. Several ultrastructural features suggested that cell wall damage resulted from an active host cell digestion. The cell wall changes were in sharp contrast with the usual normal fungal cytoplasmic appearance. Only rare intracellular debris which we supposed to represent dead yeast cells were found. These findings suggested that the yeast responsible for chromoblastomycosis resisted fungicidal activities of cutaneous macrophages which possessed the ultrastructural features of stimulated phagocytes.

Experimental pulmonary paracoccidioidomycosis in mice: morphology and correlation of lesions with humoral and cellular immune response

The present paper describes a murine model for pulmonary paracoccidioidomycosis injecting 6 X 10(5) yeast forms of Paracoccidioides brasiliensis (Pb) by the direct intratracheal route. The sequential histopathology of lung and dissemination lesions together with humoral (immunodiffusion test) and cellular immune response (footpad test and macrophage inhibition factor assay - MIF assay) were investigated since the 1st to the 360th day after infection. All infected animal showed pulmonary Pbmycosis up to Day 30; onwards the lesions subsided being found only in one mouse at Day 360. Dissemination lesions were observed in paratracheal and cervical lymph nodes in 9 out of 68 infected animals. Histologically early lesions were rich in polymorphonuclear cells and evolved to a macrophage desquamative pneumonitis at Day 15 and to typical epithelioid granulomata from Day 30 up to Day 360. Specific precipitating antibodies were first detected 15 days after infection, peaked from Day 30 to 60 and were not observed at Day 360. Significant cell-mediated immunity to Pb was noted at Day 15 with the peak reaction at Day 60 and 90. The intratracheal route represents a highly effective way of infecting mouse with Pb. This experimental pulmonary Pbmycosis is a granulomatous inflammation which courses with specific humoral and cellular immune response. It may be a good tool for further investigation in the pathogenesis and natural history of the disease.

Evaluation of skin test for chromoblastomycosis using antigens prepared from culture filtrates of Fonsecaea pedrosoi, Phialophora verrucosa, Wangiella dermatitidis and Exophiala jeanselmei

Antigenic substances were prepared from culture filtrates of Fonsecaea pedrosoi, Phialophora verrucosa, Wangiella dermatitidis and Exophiala jeanselmei. These antigenic substances were evaluated for detecting cutaneous delayed hypersensitivity in rats experimentally-infected with F. pedrosoi, P. verrucosa. W. dermatitidis, E. jeanselmei, Cladosporium carrionii and Fonsecaea compactum and in patients with chromoblastomycosis caused by F. pedrosoi. The F. pedrosoi antigen elicited positive reactions in all of the animals infected with F. pedrosoi and in 5 of 6 patients. The P. verrucosa, W. dermatitidis and E. jeanselmei antigens elicited positive reactions in all of the animals infected with the homologous species. These antigens displayed cross-reactivity in some of the animals and patients, whereas more than half of them exhibited positive reactions only to the antigens prepared from the homologous species. These results suggest that a delayed-type skin test using the antigens prepared by the authors may be useful not only for the diagnosis of chromoblastomycosis but also for the identification of species of the causative agent.