Pattern recognition receptors in fungal immunity.

Over the last decade, invasive fungal infections have emerged as a growing threat to human health worldwide and novel treatment strategies are urgently needed. In this context, investigations into host-pathogen interactions represent an important and promising field of research. Antigen presenting cells such as macrophages and dendritic cells are strategically located at the frontline of defence against potential invaders. Importantly, these cells express germline encoded pattern recognition receptors (PRRs), which sense conserved entities from pathogens and orchestrate innate immune responses. Herein, we review the latest findings regarding the biology and functions of the different classes of PRRs involved in pathogenic fungal recognition. We also discuss recent literature on PRR collaboration/crosstalk and the mechanisms involved in inhibiting/regulating PRR signalling. Finally, we discuss how the accumulated knowledge on PRR biology, especially Dectin-1, has been used for the design of new immunotherapies against fungal infections.

"Monoallelic germline methylation and sequence variant in the promoter of the RB1 gene: a possible constitutive epimutation in hereditary retinoblastoma".

BACKGROUND: Retinoblastoma is a malignant tumor of the retina in children <5 years of age and occurs after two mutations in the RB1 gene. The first mutation (M1) is germinal and confers predisposition to the hereditary type, which is transmitted as an autosomal dominant highly penetrant trait, so 90 % of carriers develop retinoblastoma; however, 10 % of carriers either do not develop the tumor or develop it unilaterally. Most mutations are point mutations. Inactivation of the RB1 gene is usually caused by mutations affecting the coding region. Silencing by methylation of the RB1 promoter has been observed in retinoblastoma tumors as a second mutation (M2) and is classified as somatic epimutation. Germline methylation of the RB1 gene promoter was studied in a particular pedigree of six generations from the paternal side, with incomplete penetrance and bias towards healthy male carriers and those affected with unilateral retinoblastoma. RESULTS: The methylation status of the 27 CpGs dinucleotides that constitute the core of the RB1 gene promoter, analyzed by cloning and genomic sequencing after DNA sodium bisulfite conversion, demonstrated a monoallelic methylation pattern which coincides with a c. [-187T > G; -188T > G] sequence variant that is found in peripheral blood lymphocytes and tumor DNA. Unexpectedly, it was the mother who transmitted this variant to two more generations. Microsatellite markers of D chromosome showed a biparental contribution of both D13 chromosomes to the retinoblastoma phenotype, conferring double heterozygosity in the affected cases. CONCLUSIONS: The monoallelic genetic-epigenetic finding, the sequence variant, and methylation suggest a constitutive epimutation and probably a genetic-epigenetic hereditary predisposition for retinoblastoma in this family.

[A simplified system for generation of germ-free zebrafish embryos and its application in Listeria monocytogenes infection].

Objective: Under conventional cultivation conditions zebrafish harbors numerous microbes from the environment, leading to activation of its innate immune systems and interfering the results of relevant studies. We aimed to establish a germ-free zebrafish embryo model suitable for studies of host immune responses to infections. Methods: A germ-free cultivation process including simple disinfection of the fertilized eggs and growth in a positive-pressured thermostatic isolator. Sterility testing of germ-free zebrafish embryos and water samples was done according to the national standards. The transcriptional level of TLRs, the mark genes indicating activation of the innate immune system, was detected by qPCR. Listeria monocytogenes was used as an infection model. Results: The cultivation system and disinfection process could ensure germ-free status as shown by absence of microbes in zebrafish embryos and egg water. TLRs were barely detectable in zebrafish raised in the germ-free system, but highly induced in conventionally raised zebrafish or in germ-free zebrafish immersion-infected with pathogenic Listeria monocytogenes. The germ-free fish was sensitive to infection by L. monocytogene EGDe at a 100-CFU dose with 100% mortality in one week, while its isogenic mutants Δmpl and ΔplcB exhibited reduced death (70% and 40%, respectively). Macrophages were recruited around the intestine in EGDe immersion infected fish, but not in Δmpl and ΔplcB infected fish. Conclusion: Zebrafish embryos produced by this simple process were free of microbes and could be used to study the innate immune responses and the pathogenesis of microbial pathogens.

The virulent Wolbachia strain wMelPop increases the frequency of apoptosis in the female germline cells of Drosophila melanogaster.

BACKGROUND: Wolbachia are bacterial endosymbionts of many arthropod species in which they manipulate reproductive functions. The distribution of these bacteria in the Drosophila ovarian cells at different stages of oogenesis has been amply described. The pathways along which Wolbachia influences Drosophila oogenesis have been, so far, little studied. It is known that Wolbachia are abundant in the somatic stem cell niche of the Drosophila germarium. A checkpoint, where programmed cell death, or apoptosis, can occur, is located in region 2a/2b of the germarium, which comprises niche cells. Here we address the question whether or not the presence of Wolbachia in germarium cells can affect the frequency of cyst apoptosis in the checkpoint. RESULTS: Our current fluorescent microscopic observations showed that the wMel and wMelPop strains had different effects on female germline cells of D. melanogaster. The Wolbachia strain wMel did not affect the frequency of apoptosis in cells of the germarium. The presence of the Wolbachia strain wMelPop in the D. melanogasterw1118 ovaries increased the number of germaria where cells underwent apoptosis in the checkpoint. Based on the appearance in the electron microscope, there was no difference in morphological features of apoptotic cystocytes between Wolbachia-infected and uninfected flies. Bacteria with normal ultrastructure and large numbers of degenerating bacteria were found in the dying cyst cells. CONCLUSIONS: Our current study demonstrated that the Wolbachia strain wMelPop affects the egg chamber formation in the D. melanogaster ovaries. This led to an increase in the number of germaria containing apoptotic cells. It is suggested that Wolbachia can adversely interfere either with the cystocyte differentiation into the oocyte or with the division of somatic stem cells giving rise to follicle cells and, as a consequence, to improper ratio of germline cells to follicle cells and, ultimately, to apoptosis of cysts. There was no similar adverse effect in D. melanogaster Canton S infected with the Wolbachia strain wMel. This was taken to mean that the observed increase in frequency of apoptosis was not the general effect of Wolbachia on germline cells of D. melanogaster, it was rather induced by the virulent Wolbachia strain wMelPop.

Retroviruses as probes for mammalian development: allocation of cells to the somatic and germ cell lineages.

Preimplantation mouse embryos were infected with a recombinant retrovirus, which serves as a genetic marker for the progeny of an infected blastomere. Quantitative analysis of proviruses carried in mosaic animals indicated that the molarity of individual proviral bands was equal in almost all tissues. The cells that give rise to the embryo proper must therefore intermingle extensively before final tissue allocation to ensure equal contribution of founder cells to all somatic tissues. The distribution of molarities of individual proviruses suggested that somatic lineages are derived from at most eight founder cells. About half of the proviruses were present in the germ line and the somatic tissues of mosaic animals, while the remaining proviruses were found either in the germ line or in the somatic tissues, but not in both. Our results suggest that at least three cells form the germ line and are set aside prior to somatic tissue allocation.

General features of persistent virus infections.

Persistent virus infections are discussed from the virus point of view in terms of the bodily sites in which the infection persists. Glands and body surfaces are thought to be significant because they give the virus protection at the topographical level from immune forces, and because they are appropriate sites for the shedding of virus to the exterior. Germ cells are relevant sites because infection can thus be transmitted vertically from generation to generation in the host. The central nervous system, however, is generally a 'dead end' from which there is no shedding to the exterior. Persistance in blood may be relevant when continued arthropod transmission becomes possible. Most persistent viruses infect lymphoreticular tissues, and this is interpreted by suggesting that it results in an impaired immune response to the infecting virus, which in turn favours persistence. It is suggested that the biological function of virus transformation and the integration of viral into host cell DNA is that it enables the infection to persist in the host and undergo reactivation. Papovaviruses, adenoviruses and oncornaviruses are considered from this point of view.

[About the infection of Drosophila female germ line cells by sigma virus (author's transl)]. / A propos de l'infection de la lignée germinale femelle de la drosophile par le virus sigma

The results which have been presented by Bregliano (1973) and Bregliano et Fleuriet (1975) in this "Annales" are discussed. The author's conclusion is that there are two distinct mechanisms for contamination of the cysts of non-stabilized females (in stabilized females, all cells, including oogonial cells, are infected in carrier state by sigma). Hypotheses are discussed.

Germ line integration and Mendelian transmission of the exogenous Moloney leukemia virus.

Mice were infected with the exogenous Moloney leukemia virus (M-MuLV) at two different stages of development. Either newborn mice (which can be considered as essentially fully differentiated animals) or preimplantation mouse embryos (at the 4-8 cell stage) were infected with M-MuLV. In both cases, animals that had developed an M-MuLV-induced leukemia were obtained. Two lines of evidence indicate that infection of preimplantation embryos, in contrast to infection of newborns, can lead to integration of the virus into the germ line. 1. Viremic males of the first backcross generation (N-1 generation) transmitted the virus to 50% of their offspring (N-2 generation) when mated with uninfected females. Likewise, a 50% transmission was observed from viremic N-2 and N-3 males to the next generations. 2. Molecular hybridization experiments revealed that viremic N-1 and N-2 animals carried one copy of M-MuLV per diploid mouse genome equivalent in all "non-target" organs tested. Together, both experiments indicate that the exogenous M-MuLV can be converted to an endogenous virus after infection of preimplantation embryos. The available evidence suggests that M-MuLV integrated into the germ line at one out of two possible integration sites. Thus, viremic backcross animals are heterozygous for a single Mendelian locus carrying the M-MuLV gene. During leukemogenesis an amplification of the M-MuLV from one copy to a maximum of four copies per diploid mouse genome equivalent takes place in the tumor tissues.