Diagnostic microarray: an array of possibilities for parasitology.

Parasites affect a majority of the world's population. Despite this fact, dreams of developing vaccines remain far off. Scientists have long studied gene expression as a hallmark of gene activities reflecting current cell conditions. Analyzing differentially expressed genes is a major initiative, and most labs recoil at the amount of time and high costs required obtaining results. By employing microarrays, researchers can decrease their reliance upon time consuming techniques; consequently, microarray is beginning to dominate other molecular diagnostic technologies. Moreover, the ability of microarrays to monitor simultaneous gene expression of thousands of genes and to produce broad arrays of data has the potential to shift the resources of the scientists from data gathering to analyzing data that are already available. As microarray technology improves and its cost decreases, the role of ability to "see" the molecular biology pathways involved in parasite host relationships will place this technology at the forefront of parasite research.

Self-tolerance in the immune privileged CNS: lessons from the entorhinal cortex lesion model.

Upon peripheral immunization with myelin epitopes, susceptible rats and mice develop T cell-mediated demyelination similar to that observed in the human autoimmune disease multiple sclerosis (MS). In the same animals, brain injury does not induce autoimmune encephalomyelitis despite massive release of myelin antigens and early expansion of myelin specific T cells in local lymph nodes, indicating that the self-specific T cell clones are kept under control. Using entorhinal cortex lesion (ECL) to induce axonal degeneration in the hippocampus, we identified possible mechanisms of immune tolerance after brain trauma. Following ECL, astrocytes upregulate the death ligand CD95L, allowing apoptotic elimination of infiltrating activated T cells. Myelin-phagocytosing microglia express MHC-II and the costimulatory molecule CD86, but lack CD80, which is found only on activated antigen presenting cells (APCs). Restimulation of invading T cells by such immature APCs (e.g. CD80 negative microglia) may lead to T cell anergy and/or differentiation of regulatory/Th3-like cells due to insufficient costimulation and presence of high levels of TGF-beta and IL-10 in the CNS. Thus, T cell -apoptosis, -anergy, and -suppression apparently maintain immune tolerance after initial expansion of myelin-specific T lymphocytes following brain injury. This view is supported by a previous metastatistical analysis which rejected the hypothesis that brain trauma is causative of MS (Goddin et al., 1999). However, concomitant trauma-independent proinflammatory signals, e.g., those evoked by clinically quiescent infections, may trigger maturation of APCs, thus shifting a delicate balance from immune tolerance and protective immune responses to destructive autoimmunity.

Turnover of rat brain perivascular cells.

Brain perivascular spaces harbor a population of cells which exhibit high phagocytic capacity. Therefore, these cells can be labeled by intraventricular injection of tracers. Such perivascular cells at the interface between blood and brain are believed to belong to the monocyte/macrophage lineage and to be involved in antigen presentation. Currently, it is unclear whether these cells undergo a continuous turnover by entering and leaving the bloodstream. Using bone-marrow-chimeric animals, migration of donor macrophages into brain perivascular spaces has been reported. On the other hand, following intracerebral injection of india ink into nontransplanted animals, ink-labeled perivascular cells were still found 2 years after injection, suggesting a high stability of this cell pool. Thus, the turnover of perivascular cells observed in chimeras might be a result of bone marrow transplantation rather than a physiological occurrence. To address this issue, we monitored de novo invasion of macrophages into perivascular spaces of apparently healthy adult rats by applying techniques other than bone marrow transplantation, (i) consecutive injections of different tracers and (ii) ex vivo isolation of macrophages from the blood, cell labeling, and reinjection into the same animal to avoid MHC mismatch. Both approaches revealed vivid de novo invasion of macrophages into perivascular spaces, but not into brain parenchyma, rendering untenable the concept of perivascular cells forming a stable population of macrophages in the brain. Thus, brain perivascular spaces are under permanent immune surveillance of blood borne macrophages in normal adult rats.