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  Mymol


  Director : DROMER Françoise (dromer@pasteur.fr)


  abstract

 

A better understanding of the interactions between the hosts and pathogenic fungi should improve the prognosis of systemic fungal infections. We thus focus our projects on Cryptococcus neoformans and Candida albicans pathogenicity by studying the host (epidemiology, cellular and animal models of infection) and the fungus (virulence factors, variability) sides.



  report

cale

Report:

Cryptococcus neoformans

Cryptococcosis is a life-threatening infection that occurs in up to 30% of patients with AIDS in tropical area in Africa and South East Asia. The most common clinical feature is a meningoencephalitis associated with a severe prognosis (³ 20% mortality) which explains the need for new prophylactic and therapeutic approaches. One of the characteristics of C. neoformans is the presence of a capsule made of polysaccharides, mainly glucuronoxylomannan (GXM). We are studying the pathophysiology of the infection and the virulence factors, among which the capsule has been shown to be the most important.

C. neoformans capsule (G. Janbon, F. Provost)

Among the evidence demonstrating a major role for the capsule in the virulence of the yeast, are the avirulence of acapsular strains and the various deleterious effects on the immune response assigned to GXM. Immunofluorescence studies with monoclonal antibodies specific for various epitopes of the GXM allowed us to demonstrate that the capsule structure is highly variable from cell to cell within a given yeast cell population. Our working hypothesis is that the variability of the capsule structure plays a role in the virulence of the yeast. The mechanisms and molecular determinants involved in the antigenic variability have been studied and uncovered for numerous procaryote and eucaryote microorganisms, but no study has been performed for pathogenic fungi. We have cloned genes (CAS) coding for proteins involved in the biosynthetic pathway leading to the cryptococcal capsule and are studying the mechanisms responsible for the capsule structure variability.

Interaction between blood-brain barrier (BBB) and C. neoformans (F. Dromer, O. Lortholary, I. Kansau, M. Lepors, L. Improvisi)

Our objective is to understand the cellular and molecular determinants that lead to the constitution of the meningoencephalitis. For this purpose, we are using two approaches. The first approach is based on the histological study of the brain structures involved in the interaction between C. neoformans and the BBB following fungemia (murine model of cryptococcosis); the second is meant at determining the parameters altering the interactions between two important cells on the host side, the endothelial cells (Human Umbilical Vein Endothelial Cells, HUVEC) and the monocytes (U937 cells) , and C. neoformans. The influence of the capsule presence (CAP64) and of the capsule structure (CAS genes) on adherence, phagocytosis and MAPK pathway is studied using isogenic pairs of strains (CAS/cas-D and CAP/cap-D).

Humoral response to C. neoformans proteins (F. Dromer, G. Janbon, S. Jacquelin)

We have demonstrated that the humoral response to proteic antigens of C. neoformans correlates with the outcome of the infection in a model of disseminated cryptococcosis in outbred mice. We have identified one of the protein associated with a humoral response in mice surviving a lethal challenge and cloned the corresponding gene. The next step will be to determine if the presence of specific antibodies in the serum from patients with cryptococcosis is predictive of the outcome and to evaluate the potential usefulness of the protein in immunotherapy. This project involves our group as well as those of Y. Germani (IP Bangui) and JL Guesdon (Ingénierie des Anticorps) (PTR).

Human cryptococcosis (F. Dromer, O. Lortholary, O. Launay, L. Improvisi, O. Ronin)

A multicentric prospective study on the pathophysiology of C. neoformans infection (Crypto A/D study) was designed in April 1997 to collect clinical data, isolates and sequential biological fluids from patients diagnosed with cryptococcosis in France (> 200 patients enrolled). We are currently analyzing the systemic (plasma) and local (CSF, BAL, urine) immune response in terms of pro- and antiinflammatory cytokines profiles according to the HIV status, the infecting serotype and the extend of the dissemination. We have shown that the CSF inflammatory response was diminished in HIV-infected patients with cryptococcal meningitis compared to what is observed in patients with other immune defects. An observational study on the management of secondary prophylaxis for cryptococcosis in HIV-infected patients under highly active antiretroviral therapy (HAART) has also been recently implemented (O. Lortholary).

Candida albicans

C. albicans is a commensal of the digestive tract responsible for a wide range of infections in immunocompetent and immunodeficient patients. Patients with prolonged neutropenia following chemotherapy or bone marrow transplantation, organ transplant recipients are at risk for candidemia. C. albicans is also responsible of nosocomial infections in surgery units, intensive care units. Apart from our participation in the Fungal Infections Network for the experimental models of candidiasis, our projects include the study of :

Biosynthesis of b-1,2 oligomannosides in C. albicans (G. Janbon, C. Mille)

Contact between C. albicans and the environment through the fungal cell wall involves interactions with various molecules, i.e. glucans (b-1,3 et b-1,6 glucose), mannans (a-1,2 et a-1,3 mannose) and mannoproteins. In addition, b-1,2 oligomannosides (associated with mannoproteins or a phospholipomannan, PLM) are found and several studies have shown that these b-1,2 oligomannosides are involved in the virulence of C. albicans. The biosynthetic pathway leading to glucans or mannoproteins have been at least partially described, whereas that leading to the b-1,2 oligomannosides are unknown. In collaboration with D. Poulain (Lille), we are identifying the genes responsible for the synthesis of the b-1,2 oligomannosides in order to facilitate the study of their influence in the pathophysiology of candidiasis.

Biofilm formation in C. albicans and Candida glabrata (G. Janbon, F. Dromer, I. Iraqui)

Biofilms are tridimentional structures composed of microorganisms that developed of various surfaces. Candida biofilms could colonize intravascular cathethers or prosthetic devices and be responsible for recurrence despite antifungal therapy. Our objective in collaboration with the groups of C. d'Enfert (Microbiologie and Environnement) and JM Ghigo (génétique des biolfilms) is to determine molecular events that lead to the development of biofilms.

National Reference Center for Mycoses and Antfungal Agents

The fields of our mission covers : the epidemiological survey of systemic fungal infections especially cryptococcosis and histoplasmosis, the monitoring of antifungal susceptibility patterns of pathogenic yeasts and filamentous fungi, the identification of rare species, the interpretation of serological tests for the diagnosis of exotic mycoses, the advice for the management of patients with mycoses (diagnosis, treatment); and evaluation of new tests or new antifungal drugs in vitro or in animal models of fungal infections.

Photos :

Photo 1 : visualization of the capsule of C. neoformans by India ink staining.

Photo 2 : Internalization of a fluorescein-labelled yeast (C. neoformans) by the monocytic cell line U937 (confocal microscopy)



  publications

puce Publications of the unit on Pasteur's references database


  personnel

  Office staff Researchers Scientific trainees Other personnel
  MARTIN Edith , emartin@pasteur.fr

DROMER, Françoise, dromer@pasteur.fr

JANBON, Guilhem, janbon@pasteur.fr

LORTHOLARY, Olivier, olortho@pasteur.fr

CHABASSE, Christine

GONTIER, Catherine

KANSAU, Imad

LEPORS, Marina

MILLE, Céline

IMPROVISI, Luce

LAUNAY, Odile

JACQUELIN, Sébastien

PROVOST, Frédérique

RONIN, Olivier


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