Dynamics of macrophage cell populations during murine pulmonary tuberculosis

The influx of macrophages into the lungs is the major component of the granulomatous response to infection with Mycobacterium tuberculosis. In this investigation we used flow cytometric analysis to define macrophage populations entering the airways and lung tissues of infected mice. We demonstrate that by the judicious use of cell surface markers, especially CD11b and CD11c, several cell populations can be distinguished, allowing cell sorting and morphological definition. Primary populations of CD11b(-)/CD11c(+/high) were defined as alveolar macrophages, CD11b(high)/CD11c(+/high) as dendritic cells, and CD11b(+/mid)/CD11c(+/mid) as small macrophages or monocytes, and changes in the activation phenotype of these populations were followed over the early course of the infection. In further studies, these cell populations were compared with cells harvested during the chronic stage of the disease. During the chronic stage of infection, Ag-presenting class II molecules and activation markers were poorly expressed on dendritic, small macrophage, and monocyte cell populations, which may have important implications for the breakdown of the lesions during reactivation disease. This analytical approach may facilitate the further characterization of macrophage populations entering into the lung tissues and their relative contributions to host resistance to tuberculosis infection.     

Comparison of MultiMap and TSP/CONCORDE for constructing radiation hybrid maps

Radiation hybrid (RH) map construction allows investigators to locate both type I and type II markers on a given genome map. The process is composed of two steps. The first consists of determining the pattern distribution of a set of markers within the different cell lines of an RH panel. This is mainly done by polymerase chain reaction (PCR) amplification and gel electrophoresis, and results in a series of numbers indicating the presence or the absence of each marker in each cell line. The second step consists of a comparison of these numbers, using various algorithms, to group and then order markers. Because different algorithms may provide (slightly) different orders, we have compared the merits of the MultiMap and TSP/CONCORDE packages using a data set of information currently under analysis for construction of the canine genome RH map.     

H2AX regulates meiotic telomere clustering

The histone H2A variant H2AX is phosphorylated in response to DNA double-strand breaks originating from diverse origins, including dysfunctional telomeres. Here, we show that normal mitotic telomere maintenance does not require H2AX. Moreover, H2AX is dispensable for the chromosome fusions arising from either critically shortened or deprotected telomeres. However, H2AX has an essential role in controlling the proper topological distribution of telomeres during meiotic prophase I. Our results suggest that H2AX is a downstream effector of the ataxia telangiectasia-mutated kinase in controlling telomere movement during meiosis.     

Human serum albumin and its structural variants mediate cholesterol efflux from cultured endothelial cells

In the present study, we used the human EA.hy926 endothelial cell line as the model system to investigate the effect of human serum albumin (HSA) and its structural variants on cholesterol efflux. Initial studies showed that HSA promoted cholesterol efflux in a dose- and time-dependent manner, reaching a plateau at 10 mg/ml at 90 min. As a control, gelatin displayed no significant effect on efflux, while HSA was significantly more efficient than ovalbumin and bovine serum albumin (BSA) in promoting cholesterol efflux. Equal molar concentrations of HSA and apolipoprotein A-I (apoA-I) showed that apoA-I had considerably higher efficiency in efflux. However, the prevailing high plasma concentrations of HSA may compensate for its lower efflux rate compared to apoA-I. To characterize the mechanism of HSA-mediated cholesterol efflux, we studied the effects of cAMP and temperature on efflux using both EA.hy926 endothelial cells and murine RAW 264.7 macrophages. We found that HSA-mediated efflux occurred via a cAMP-independent and relatively temperature-insensitive pathway. We next examined the nature of HSA-cholesterol interaction by comparing the effects of various HSA mutants to wild-type HSA on cholesterol efflux. We found specific interactions between subdomains 2A and 3A and cholesterol, as indicated by the changes in the efflux rate of various HSA mutants. In conclusion, our study provides evidence for the role of HSA in cholesterol efflux, and shows that the substitution of specific amino acid residues in subdomains of 2A and 3A may be important structural determinants in its ability to bind to cholesterol and participate in cholesterol efflux.     

Atomic force microscopy and light scattering of small unilamellar actin-containing liposomes

Three-dimensional networks of filamentous actin (F-actin) encapsulated inside phosphatidylcholine liposomes are currently being used in an effort to model the cytoskeleton and plasma membrane of eukaryotic cells. In this article, unilamellar lipid vesicles consisting of egg yolk-derived phosphatidylcholine encapsulating monomeric actin (G-actin) were made via extrusion in low ionic strength buffer (G-buffer). Vesicle shape and structure in these dispersions was studied using a combination of fluid-tapping atomic force microscopy, and multiangle static light scattering. After subjecting the liposome dispersion to high ionic strength polymerization buffer (F-buffer) containing K(+) ions, atomic force microscopy imaging and light scattering of these liposomes indicated the formation of specialized structures, including an overall liposome structure transformation from spherical to torus, disk-shaped geometries and tubular assemblies. Several atomic force microscopy control measurements were made to ascertain that the specialized structures formed were not due to free G-actin and F-actin self-assembling on the sample surface, plain liposomes exposed to G- and F-buffer, or liposomes encapsulating G-actin. Liposomes encapsulating G-actin assumed mostly thin disk shapes and some large irregularly shaped aggregates. In contrast, liposomes encapsulating polymerized actin assumed mostly torus or disk shapes along with some high aspect ratio tubular structures.     

Dynamical and integrative cell signaling: challenges for the new biology

Years of careful experimental analysis have revealed that signaling molecules are organized into complex networks of biochemical reactions exquisitely regulated in time and space to provide a cell with high-fidelity information about an extremely noisy and volatile environment. A new view of signaling networks as systems consisting of multiple complex elements interacting in a multifarious fashion is emerging, a view that conflicts with the single-gene or protein-centric approach common in biological research. The postgenomic era has brought about a different, network-centric methodology of analysis, suddenly forcing researchers toward the opposite extreme of complexity, where the networks being explored are, to a certain extent, intractable and uninterpretable. Both the cartoons of simple pathways and the very large "hair-ball" diagrams of large intracellular networks are also representations of static worlds, superficially devoid of dynamics and chemistry. These representations are often viewed as being analogous to stably linked computer and neural networks rather than dynamically changing networks of chemical interactions, where the notions of concentration, compartmentalization, and diffusion may be the primary determinants of connectivity. Arguably, the systems biology approach, relying on computational modeling coupled with various experimental techniques and methodologies, will be an essential component of analysis of the behavior of signal transduction pathways. Combining the dynamical view of rapidly evolving responses and the structural view arising from high-throughput analyses of the interacting species will be the best approach toward efforts toward greater understanding of intracellular signaling processes.     

Low-level iron-dependent mutants of Listeria monocytogenes and their virulence in macrophages

Listeria monocytogenes is an opportunistic intracellular pathogen capable of growth that requires iron for growth within phagocytic cells and virulence expression. In the presence of an appropriate concentration tropolone, an iron-chelating agent, growth of L. monocytogenes is completely inhibited. However, this inhibition can be relieved by addition of dopamine, norepinephrine, or ferric citrate. By selection on streptonigrin medium supplemented with tropolone and norepinephrine, we have obtained two spontaneous mutants, Lm-8 and Lm-15, with the same iron dependence but lower iron dependence than the wild-type Lm-B38. The association between iron requirement and virulence of the two mutants and the wild type was studied in the J774 macrophage cell line. One hour after phagocytosis by the J774 macrophage cell line, the two mutants and the parental strain displayed no difference in the number of phagocytosed bacteria. Twenty-four hours after phagocytosis, the number of bacteria within the surviving macrophages was identical for the wild strain and the two clones. However, only 40% of macrophage cells infected with Lm-8 and 90% of those infected with Lm-15 were alive after 24 h in comparison with macrophage cells infected with the parental strain Lm-B38. These data demonstrate that there is no direct correlation between iron requirement and virulence of L. monocytogenes in the J774 macrophage cell line.