Membrane Dynamics and Organization of the Phagocyte NADPH Oxidase in PLB-985 Cells

Neutrophils are the first cells recruited at the site of infections, where they phagocytose the pathogens. Inside the phagosome, pathogens are killed by proteolytic enzymes that are delivered to the phagosome following granule fusion, and by reactive oxygen species (ROS) produced by the NADPH oxidase. The NADPH oxidase complex comprises membrane proteins (NOX2 and p22^phox), cytoplasmic subunits (p67^phox, p47^phox, and p40^phox) and the small GTPase Rac. These subunits assemble at the phagosomal membrane upon phagocytosis. In resting neutrophils the catalytic subunit NOX2 is mainly present at the plasma membrane and in the specific granules. We show here that NOX2 is also present in early and recycling endosomes in human neutrophils and in the neutrophil-like cell line PLB-985 expressing GFP-NOX2. In the latter cells, an increase in NOX2 at the phagosomal membrane was detected by live-imaging after phagosome closure, probably due to fusion of endosomes with the phagosome. Using super-resolution microscopy in PLB-985 WT cells, we observed that NOX2 forms discrete clusters in the plasma membrane. The number of clusters increased during frustrated phagocytosis. In PLB-985NCF1ΔGT cells that lack p47^phox and do not assemble a functional NADPH oxidase, the number of clusters remained stable during phagocytosis. Our data suggest a role for p47^phox and possibly ROS production in NOX2 recruitment at the phagosome.

Fluorescence correlation spectroscopy to study diffusion and reaction of bacteriophages inside biofilms

In the natural environment, most of the phages that target bacteria are thought to exist in biofilm ecosystems. The purpose of this study was to gain a clearer understanding of the reactivity of these viral particles when they come into contact with bacteria embedded in biofilms. Experimentally, we quantified lactococcal c2 phage diffusion and reaction through model biofilms using in situ fluorescence correlation spectroscopy with two-photon excitation. Correlation curves for fluorescently labeled c2 phage in nonreacting Stenotrophomonas maltophilia biofilms indicated that extracellular polymeric substances did not provide significant resistance to phage penetration and diffusion, even though penetration and diffusion were sometimes restricted because of the noncontractile tail of the viral particle. Fluctuations in the fluorescence intensity of the labeled phage were detected throughout the thickness of biofilms formed by c2-sensitive and c2-resistant strains of Lactococcus lactis but could never be correlated with time, revealing that the phage was immobile. This finding confirmed that recognition binding receptors for the viral particles were present on the resistant bacterial cell wall. Taken together, our results suggest that biofilms may act as "active" phage reservoirs that can entrap and amplify viral particles and protect them from harsh environments.

[Determination, by in situ hybridization on interphasic nucleus, a cytogenetic DNA index; application to breast cancer; comparison of this DNA index to DNA indexes determined by imaging and flow cytometry]

In oncology, flow cytometry (FCM) and image cytometry (ICM) are commonly used to detect DNA aneuploid cell populations in solid tumors. Agreement between these two approaches is good. The use of both techniques in association minimizes the rate of FCM and ICM false negatives and gives better DNA pattern characterization, particularly for detection of any tumoral component in the FCM DNA diploid peak. Nevertheless, discrepancies exist between the FCM and the ICM DNA index values: the ICM DNA index is often greater than the FCM DNA index. The aim of the present study was to establish a cytogenetic DNA index by determining the chromosomal ploidy using a molecular cytogenetic approach and to compare it to the FCM and ICM DNA indexes. We present here the fluorescence in situ hybridization (FISH) technique we have adapted to the study of breast cancer in order to count the number of copies of the 22 + X human chromosomes in interphasic nuclei. This was achieved using a panel of 21 indirect FITC labeled probes which recognize specific chromosomic DNA sequences. Preliminary results obtained from DNA diploid and DNA aneuploid tumors are discussed.