Interactions of F1 fractions from different strains of Paracoccidioides brasiliensis with human complement and with human neutrophils

Anti-Immune Strategies of Pathogenic Fungi

Pathogenic fungi have developed many strategies to evade the host immune system. Multiple escape mechanisms appear to function together to inhibit attack by the various stages of both the adaptive and the innate immune response. Thus, after entering the host, such pathogens fight to overcome the immune system to allow their survival, colonization and spread to different sites of infection. Consequently, the establishment of a successful infectious process is closely related to the ability of the pathogen to modulate attack by the immune system. Most strategies employed to subvert or exploit the immune system are shared among different species of fungi. In this review, we summarize the main strategies employed for immune evasion by some of the major pathogenic fungi.

The paracoccidioides cell wall: past and present layers toward understanding interaction with the host

The cell wall of pathogenic fungi plays import roles in the interaction with the host, so that its composition and structure may determine the course of infection. Here we present an overview of the current and past knowledge on the cell wall constituents of Paracoccidioides brasiliensis and P. lutzii. These are temperature-dependent dimorphic fungi that cause paracoccidioidomycosis, a systemic granulomatous, and debilitating disease. Focus is given on cell wall carbohydrate and protein contents, their immune-stimulatory features, adhesion properties, drug target characteristics, and morphological phase specificity. We offer a journey toward the future understanding of the dynamic nature of the cell wall and of the changes that may occur when the fungus infects the human host.

Diversity in Paracoccidioides brasiliensis. The PbGP43 gene as a genetic marker

Paracoccidioides brasiliensis is a temperature-dependent dimorphic fungus and the agent of paracoccidioidomycosis (PCM), which is prevalent in rural workers of Latin American countries. Until a decade ago, most of the studies involving P. brasiliensis used clinical isolates, since environmental samples from soil are difficult to obtain. More recently, P. brasiliensis has been isolated from infected wild and domestic animals, especially from the nine-banded armadillo Dasypus novemcinctus in Brazil. Over the years, diversity within the species has been observed at several phenotypic levels. The present review will discuss the reports focusing on genetic polymorphism, which culminated with the detection of P. brasiliensis phylogenetic species as a result of a multilocus study. Polymorphism in the PbGP43 gene is detailed. This gene encodes fungal glycoprotein gp43, a dominant P. brasiliensis antigen largely studied in the last two decades for its importance in diagnosis, immune protection, and adhesive properties to extracellular matrix-associated proteins. Fungal traits associated with genetic groups are discussed.

Complement and fungal pathogens: an update

Fungal infections are a serious complication in immunocompromised patients such as human immunodeficiency virus-infected individuals, patients with organ transplantations or with haematological neoplasia. The lethality of opportunistic fungal infection is high despite a growing arsenal of antimycotic drugs, implying the urgent need for supportive immunological therapies to strengthen the current inefficient antimicrobial defences of the immunocompromised host. Therefore, increasing effort has been directed to investigating the interplay between fungi and the host immunity and thus to find starting points for additional therapeutic approaches. In this article, we review the actual state of the art concerning the role of complement in the pathogenesis of fungal infections. Important aspects include the activation of the complement system by the fungal pathogen, the efficiency of the complement-associated antimicrobial functions and the arsenal of immune evasion strategies applied by the fungi. The twin functions of complement as an interactive player of the innate immunity and at the same time as a modulator of the adaptive immunity make this defence weapon a particularly interesting therapeutic candidate to mobilise a more effective immune response and to strengthen in one fell swoop a broad spectrum of different immune reactions. However, we also mention the 'Yin-Yang' nature of the complement system in fungal infections, as growing evidence assigns to complement a contributory part in the pathogenesis of fungus-induced allergic manifestations.

Investigation of the role of complement and complement receptors in the modulation of B cell activation by a Paracoccidioides brasiliensis cell wall fraction

F1 fraction from Paracoccidioides brasiliensis is a potent activator of the complement system. Considering that complement receptors CR1 and CR2 are involved in the regulation of B cell response, we evaluated the in vitro effect of the F1 in the activation of B lymphocytes, as well as the participation of complement receptors in this process. Murine splenocytes were cultured in order to evaluate the expression of CD40, CD45RB and CD69 on B lymphocyte, and IgG and IgM were quantified in the culture supernatant. F1 participated in the activation of B cells, showing a positive modulation effect on all markers analyzed. An increase in the production of IgG was detected in the supernatants when the opsonized F1 fraction was present. Complement receptor blockade with monoclonal antibodies led to a partial reduction in immunoglobulin secretion, suggesting that these receptors, especially CR2, play a role in modulating the function of B lymphocyte stimulated with the opsonized F1 fraction. These results may contribute for a better understanding of the B cell activation and differentiation processes in response to the F1 fraction from P. brasiliensis.

The role of complement in invasive fungal infections. Die Rolle des Komplements bei invasiven Pilzinfektionen

New therapeutic approaches enable organ transplantations and guarantee longer survival for AIDS patients or patients with haematological neoplasia. The price for these medical advances is immunosuppression and thus enhanced susceptibility to opportunistic fungal infections. As a consequence invasive fungal infections are on the march in modern medicine. Therapeutic limitations and difficulties strongly demand for a deeper understanding of the interaction between the various fungi and the hosts' innate and adaptive immune defence system. This understanding is the essential prerequisite for a potential therapeutic approach, which may support specifically the insufficient antifungal attack of the host. In the present article, we therefore review the current knowledge of the role of the complement system as a central part of innate immunity and as a fine tuner of adaptive immunity in the pathogenesis of invasive fungal infections, such as aspergillosis, candidosis, cryptococcosis, paracoccidioidomycosis, blastomycosis and histoplasmosis.

Leukotrienes are involved in leukocyte recruitment induced by live Histoplasma capsulatum or by the beta-glucan present in their cell wall

1. The inflammatory cell influx towards the peritoneal cavity in mice inoculated i.p. with live or dead Histoplasma capsulatum or with its subcellular preparations was studied. We also evaluated the effects of dexamethasone (Dexa) or MK886, an inhibitor of leukotriene (LT) biosynthesis, on the recruitment of leukocytes. 2. Live yeast form of fungus (LYH) induced an increase in neutrophils (NE) which was highest 4 to 24 h after inoculation. Mononuclear cell (MN) migration beginning at 24 h with a gradual increase over 48 and 168 h, and an eosinophil (EO) recruitment occurs between 24 and 48 h. 3. NE and EO recruitment induced by dead mycelial form of fungus (DMH) was greater than that observed for dead yeast form of fungus (DYH). A similar leukocyte migration pattern was seen after i.p. injection of the alkali-insoluble fraction (F1) from DYH (F1Y) and F1 from DMH (F1M) this being more active than former. The difference in concentration of beta-glucan in DYH and DMH could explain the different inflammatory capacity exhibited by the two forms of H. capsulatum. 4. LT seems to be the principal mediator of leukocyte migration in response to LYH, DYH or DMH or to beta-glucan. However, other mediators appear to contribute to NE and EO migration since the treatment with Dexa was more effective in inhibiting cell migration than MK886. Complement dependent leukocyte migration may participate in this recruitment. Treatment with MK886 completely abolished MN cell migration, indicating its dependence on the presence of LT.

Correlation of alternative pathway (AP) lytic activity and AP-dependent neutrophil phagocytosis with factor B levels and consumption in serum

This work investigated the correlation between serum levels of factor B, AP-lytic activity, ratio of factor B activation by zymosan, and AP-dependent neutrophil phagocytosis in samples of normal human serum (NHS). In addition, since the antithyroid drug propylthiouracil (PTU) induces increased levels of AP lytic activity in rats, groups of these animals were treated with this drug in order to increase AP titers and to evaluate those parameters also in this condition. The results showed no correlation between factor B concentration and AP lytic activity in 18 samples of NHS or between factor B concentration and proportion of consumption by zymosan. Interestingly, this consumption was also not correlated with phagocytosis as measured by the chemiluminescence (CL) response of neutrophils to the opsonized particles. The two biological properties of phagocytosis and lytic activity, dependent of AP, were not correlated to each other in the NHS samples. In the samples of rat serum with increased AP lytic levels a different result was observed. A positive correlation between CL response and lytic activity occurred in serum of animals receiving a low PTU dose, but not in serum of animals receiving a high dose, where CL responses were lower than those of controls. The results are compared to literature data and discussed in terms of individual differences in resistance or susceptibility to infections and or diseases involving the complement system.