Candida albicans hyphal form enhances tumor necrosis factor mRNA levels and protein secretion in murine ANA-1 macrophages

Candida albicans Yeast, Pseudohyphal, and Hyphal Morphogenesis Differentially Affects Immune Recognition

Candida albicans is a human opportunist pathogen that can grow as yeast, pseudohyphae, or true hyphae in vitro and in vivo, depending on environmental conditions. Reversible cellular morphogenesis is an important virulence factor that facilitates invasion of host tissues, escape from phagocytes, and dissemination in the blood stream. The innate immune system is the first line of defense against C. albicans infections and is influenced by recognition of wall components that vary in composition in different morphological forms. However, the relationship between cellular morphogenesis and immune recognition of this fungus is not fully understood. We therefore studied various vegetative cell types of C. albicans, singly and in combination, to assess the consequences of cellular morphogenesis on selected immune cytokine outputs from human monocytes. Hyphae stimulated proportionally lower levels of certain cytokines from monocytes per unit of cell surface area than yeast cells, but did not suppress cytokine response when copresented with yeast cells. Pseudohyphal cells induced intermediate cytokine responses. Yeast monomorphic mutants had elevated cytokine responses under conditions that otherwise supported filamentous growth and mutants of yeast and hyphal cells that were defective in cell wall mannosylation or lacking certain hypha-specific cell wall proteins could variably unmask or deplete the surface of immunostimulatory ligands. These observations underline the critical importance of C. albicans morphology and morphology-associated changes in the cell wall composition that affect both immune recognition and pathogenesis.

Adaptive response of microglial cells to in vitro infection by Candida albicans isolates with different genomic backgrounds

It has been recently demonstrated that Candida albicans isolates with distinct genomic backgrounds (namely, b and c genotypes) express different susceptibility to antifungal activity by human monocytes in vitro. We show here that, although comparable in their ability to undergo dimorphic transition and in susceptibility to phagocytosis by microglial cells, the b and c isolates show striking differences in terms of intracellular survival. Only the c genotype resists indeed to intracellular killing and eventually replicates inside microglial cells, that in turn respond to fungal infection, preferentially towards the c genotype, with nuclear factor-kappaB (NF-kappaB) activation and increased Mip1alpha production. These data indicate that C. albicans-microglial cell interaction is strictly dependent upon fungal genotype, strengthening the potential significance of genotyping as prognostic parameter in clinical infections by C. albicans.

Candida albicans stress mannoprotein, SMP200, enhances tumour necrosis factor secretion in the murine macrophage cell line ANA-1

Tumour necrosis factor (TNF) secretory activity has been studied in the murine macrophage cell line ANA-1 following in vitro exposure to Candida albicans 200 kDa stress mannoprotein (SMP200). Treatment of ANA-1 murine macrophages with 200 kDa stress mannoprotein results in increased TNF secretion. The phenomenon is (i) dose- and time-dependent, (ii) abrogated by 200 kDa stress mannoprotein preincubation with a specific monoclonal antibody, and (iii) dependent on intact murine macrophage Ca2+/calmodulin-dependent protein kinase function.

Production of IL-6 and TNF-alpha by the macrophage-like cell line RAW 264.7 after treatment with a cell wall extract of Candida albicans

Treatment of the cell wall of Candida albicans with ethylenediamine yields an extract that is antigenic for both the humoral and cell-mediated arms of the immune system. This extract has been shown in previous studies by this laboratory and others to possess potent immunomodulatory activity. We report results here that show that treatment of the macrophage-like cell line RAW 264.7 with the ethylenediamine cell wall (EDA-CW) extract results in an increase in the production of both interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha). Our results also show that the EDA-CW extract possess potent costimulatory activity when combined with interferon-gamma (IFN-gamma). We have found, on the other hand, that EDA-CW extract-treated cells fail to produce elevated levels of IL-1 either alone or in combination with IFN-gamma as a costimulus. Our analysis also shows that the activation of TNF-alpha production by the EDA-CW extract appears to be at the level of transcription, since Northern blot analysis shows that the increase in the level of TNF-alpha mRNA is essentially identical to the rise in TNF-alpha activity released. We suggest that a component of the immunomodulatory activity of the EDA-CW extract is via the activation of macrophage function.

Dynamic production of tumour necrosis factor-alpha (TNF-alpha) messenger RNA, intracellular and extracellular TNF-alpha by murine macrophages and possible association with protein tyrosine phosphorylation of STAT1 alpha and ERK2 as an early signal

Tumour necrosis factor-alpha (TNF-alpha), an important mediator in both immune and inflammation responses, is one of the major cytokines released by activated macrophages. The present study shows that, during macrophage activation, protein tyrosine phosphorylation of STAT1 alpha and ERK2 occurred as an immediate early signal, whereas maximum TNF-alpha mRNA transcription appeared at 3 hr, precursor TNF-alpha formation at 3 to 4 hr, and TNF-alpha release at 5 to 6 hr after stimulation of an RPMI-1640-based induction medium containing lipopolysaccharide (100 ng/ml), interferon-gamma (100 U/ml), and 0.5% bovine serum albumin. Herbimycin A, a tyrosine kinase inhibitor, suppresses protein tyrosine phosphorylation of STAT1 alpha and ERK2 and also blocks TNF-alpha production by resident peritoneal macrophages from BALB/c mice, suggesting a possible association between protein tyrosine phosphorylation of STAT1 alpha and ERK2 and macrophage activation resulting in TNF-alpha production.

Activation of murine resident peritoneal macrophages by a cell wall extract of Candida albicans

Ethylenediamine extraction of the cell walls of Candida albicans yields an extract which possesses antigenic activity, and like other whole cell and cell wall preparations of Candida, has been shown previously to possess immunomodulatory activity. We report here results which show that non-elicited, resident peritoneal macrophages treated with the ethylenediamine cell wall extract exhibit morphological characteristics of activated macrophages. Treated cells also manifest an increased respiratory burst response and secrete elevated levels of IL-6. The treatment with the extract appears to provide a co-priming signal to the resting macrophages, since co-stimulation with interferon-gamma results in an increased level of IL-6 and IL-1. Our results also show that extract-treated cells manifest increased responsiveness to a lipopolysaccharide as measured by the production of tumour necrosis factor-alpha. These results provide an additional basis for our understanding of the immunomodulatory activity of components of the Candida cell wall.

Influence of the Bcg locus on macrophage response to the dimorphic fungus Candida albicans

The Bcg/Ity/Lsh gene (candidate Nramp) controls natural resistance to several parasites, such as Mycobacterium bovis, Leishmania donovani, and Salmonella typhimurium. Using two macrophage (M phi) cell lines (B10R and B10S) derived from mouse strains congenic at Bcg, we found that M phi s from resistant mice (B10R M phi s) act more effectively against the two morphogenetic forms of the dimorphic fungus Candida albicans compared with M phi s from susceptible mice (B10S M phi s). Moreover, when assessed for tumor necrosis factor secretion in response to the hyphal form of C. albicans, B10R M phi s are significantly more effective at expressing this secretory function than are B10S M phi s, closely resembling the trend of response to lipopolysaccharide. Overall, these results provide insight into the influence of the Bcg locus on the M phi response to C. albicans.

Comparative studies on functional and secretory properties of macrophage cell lines derived from different anatomical sites

In the present study, we compared four macrophage (M phi) cell lines from different anatomical origins for functional and secretory activities against the two morphogenetic forms of the fungus Candida albicans. We show that all the cell lines actively phagocytize the yeast and exert antimicrobial activity against both forms of Candida, although M phi of microglial origin are the most effective. When assessed for secretory properties, microglial M phi exhibit a peculiar pattern with respect to other M phi populations under either basal or stimulated conditions. In particular, only microglial M phi fail to respond to the hyphal form of the fungus (H-Candida), which instead acts as a potent tumor necrosis factor inducer in the other M phi cell lines. When exposed to H-Candida, microglial M phi are indistinguishable from other M phi in their ability to modulate specific surface adhesion molecules. In addition to strengthening the knowledge on functional heterogeneity among M phi, our data provide evidence on the peculiar behavior of microglial M phi. To what extent M phi heterogeneity may be related to tissue homeostasis is discussed.

Tumor necrosis factor as an autocrine and paracrine signal controlling the macrophage secretory response to Candida albicans

We have previously demonstrated that the hyphal form of Candida albicans (H-Candida), but not the yeast form (Y-Candida), acts as a macrophage-stimulating agent. The early response (1 to 3 h) of the macrophage cell line ANA-1 to H-Candida results in enhanced tumor necrosis factor (TNF) transcription and production. Here we show that when coincubation times are prolonged (3 to 24 h), Y-Candida also exhibits stimulatory properties. This phenomenon has been ascribed to the occurrence of the dimorphic transition, as demonstrated by microscopic evaluation of the cultures and by experiments in which both killed Y-Candida and the agerminative strain C. albicans PCA-2 failed to induce cytokine production. TNF produced in response to H-Candida acts as an autocrine and paracrine signal controlling the macrophage secretory response to C. albicans. In fact, addition of anti-TNF polyclonal antibodies to the coculture of ANA-1 macrophages and H-Candida results in a marked and time-dependent decrease of TNF transcript levels. Moreover, pretreatment of macrophages with recombinant TNF for 3 h enhances TNF and induces interleukin-1 production in response to both forms of Candida, while pretreatment for 18 h renders macrophages refractory to any stimuli. Interestingly, the kinetics of interleukin-1 transcription and secretion in response to H-Candida are delayed with respect to those of TNF. Overall, these data indicate that TNF, produced by macrophages in response to H-Candida, regulates its own production as well as that of other soluble factors, thus suggesting that this cytokine plays multiple roles in the immune mechanisms involved in Candida infection.

Preincubation of Candida albicans strains with amphotericin B reduces tumor necrosis factor alpha and interleukin-6 release by human monocytes

The release of tumor necrosis factor alpha (TNF-alpha) and interleukin-6 (IL-6) by human monocytes stimulated with whole heat-killed Candida albicans CA3 (a clinical isolate) and CA2 (a germ tube-negative mutant) either treated or not treated with amphotericin B was investigated. The optimal release of the cytokines was observed at 24 h of incubation of the yeasts with the monocytes for both TNF-alpha and IL-6. The levels ranged from 10,500 to 19,000 U/ml for TNF-alpha and from 350 to 460 pg/ml for IL-6. Germ tube-negative mutant CA2 induced the release of TNF-alpha at levels significantly (P < 0.05) lower than those induced by clinical isolate CA3, while no major differences were observed between the two strains with regard to their capacity to induce the release of IL-6. In all instances, preincubation of the yeasts with a sublethal concentration of amphotericin significantly reduced cytokine production. These results suggest that drug-induced alterations of fungal outer structures may affect the interactions between the yeasts and the monocytes, resulting in a reduced level of secretion of cytokines.

Fever produced by the fungus T. beigelii infused into the anterior hypothalamic preoptic area of the rat

Previously it was reported that a control saline solution infused into the anterior hypothalamic, preoptic area (AH/POA) can induce an intense fever from an unknown source. To avoid such fevers, cerebral dialysis has been proposed as an alternative procedure, although in nearly all experiments on the febrile response, a nonpyrogenic solution is injected, not dialyzed, directly into the AH/POA. The purpose of this study was to determine the: a) possible conditions whereby a control solution can cause an experimental fever; b) putative organisms which may comprise the source of a centrally induced fever; and c) procedures whereby such fevers can be avoided. In twelve adult male Sprague-Dawley rats, an intracerebral cannula for microinjections and a Minimitter temperature transmitter were implanted within the AH/POA and intraperitoneal cavity, respectively. Following recovery, the thermoreactivity of each site in the AH/POA was verified by a microinjection of norepinephrine which typically lowers body temperature (Tb) by 0.5-1.0 degrees C. Two artificial cerebrospinal fluid (CSF) test solutions were used: one exposed to the ambient conditions of the laboratory, and a second prepared under pathogen-free conditions, including filtration, to exclude biological contaminants. A rise in temperature of 0.8-1.0 degrees C within 1.0 h after microinjection, which increased to as high as 3.5 degrees C within 4 h, typically was produced by the contaminated artificial CSF solution. The filtered CSF did not evoke a consistent or reliable rise in Tb of the rats.(ABSTRACT TRUNCATED AT 250 WORDS)