Neuronal plasticity and cellular immunity: shared molecular mechanisms

Sex and the MHC

Major histocompatibility complex class Ib molecules may play a surprising role in pheromone detection in mammals.

In vitro expression of major histocompatibility class I and class II antigens by conditionally immortalized murine neural stem cells

The expression of major histocompatibility complex (MHC) antigens on the surface of cells is intimately linked to in vivo graft survival. It has been previously shown that the conditionally immortalized temperature-sensitive Maudsley hippocampal clone 36 (MHP36) neural stem cells show good long-term graft survival and do not elicit an acute immunological response following transplantation. Here we report that MHP36 cells express both MHC class I and class II antigens when grown in culture under proliferative conditions (33 degrees C), whereas cells with a differentiated morphology in the non-proliferative (37-39 degrees C) condition express low to undetectable levels of either MHC molecules. However, morphologically undifferentiated cells persisting under non-proliferating conditions continued to express both MHC antigens. The downregulation of MHC antigens upon differentiation following cell transplantation could therefore contribute to the graft survival of MHP36 cells.

Effects of interferon-gamma on neuronal infections

IFN-gamma is released in the brain, not only during acute infectious diseases or immunological reactions, but also for extended periods of time after clearance of infectious virus and during viral latency. In this review, we focus on the role of IFN-gamma in the interaction between a neuron and a pathogen, that is, the role in implementation of microbial destruction, stasis or persistence, its potential neuroprotective or toxic effects, and how this cytokine may affect neuronal function and the behavior of an individual.

Induction of MHC class II antigens on cells of the inner ear

Growing evidence supports the concept that immune reactions occur in the cochlea, where they can function either in protection or as a source of inflammation. Since immunity is generally initiated by antigen presentation of foreign substances to T cells, antigen-presenting cells expressing major histocompatibility complex (MHC) class II molecules are required. Under resting conditions, cochlear cells usually express no MHC class II. However, we show that exposure to -interferon in vitro induces an increase in MHC class II expression in neonatal cochlear cells of mice. In addition, MHC class II immunoreactivity was observed in the inner ear of adult mice after induction of sterile labyrinthitis in vivo. It is concluded that the induction of MHC class II molecules by inflammation may render cochlear cells competent to initiate and participate in immune reactions and may therefore contribute to both immunoprotective and immunopathological responses of the inner ear.

Induced neuronal expression of class I major histocompatibility complex mRNA in acute and chronic inflammation models

Studies have demonstrated neuronal expression of class I major histocompatibility complex (MHC) mRNA and protein in normal and developing brain and in response to injury or viral infection. We report neuronal expression of class I MHC mRNA in hypothalamic paraventricular nucleus (PVN) neurons in rats following systemic infection with Trypanosoma brucei brucei parasites (chronic) and in response to intravenous 1 mg/kg lipopolysaccharide administration (acute peripheral) and in striatal neurons following intrastriatal 5 microg lipopolysaccharide injection (acute central). These results demonstrate that neurons can be a source of immune signaling molecules and establish class I MHC as part of the neuronal component of immune responses.

The newt ortholog of CD59 is implicated in proximodistal identity during amphibian limb regeneration

The proximodistal identity of a newt limb regeneration blastema is respecified by exposure to retinoic acid, but its molecular basis is unclear. We identified from a differential screen the cDNA for Prod 1, a gene whose expression in normal and regenerating limbs is regulated by proximodistal location and retinoic acid: Prod 1 is the newt ortholog of CD59. Prod 1/CD59 was found to be located at the cell surface with a GPI anchor which is cleaved by PIPLC. A proximal newt limb blastema engulfs a distal blastema after juxtaposition in culture, and engulfment is specifically blocked by PIPLC, and by affinity-purified antibodies to two distinct Prod 1/CD59 peptides. Prod 1 is therefore a cell surface protein implicated in the local cell-cell interactions mediating positional identity.

Inflammation in neurodegenerative disease--a double-edged sword

Inflammation is a defense reaction against diverse insults, designed to remove noxious agents and to inhibit their detrimental effects. It consists of a dazzling array of molecular and cellular mechanisms and an intricate network of controls to keep them in check. In neurodegenerative diseases, inflammation may be triggered by the accumulation of proteins with abnormal conformations or by signals emanating from injured neurons. Given the multiple functions of many inflammatory factors, it has been difficult to pinpoint their roles in specific (patho)physiological situations. Studies of genetically modified mice and of molecular pathways in activated glia are beginning to shed light on this issue. Altered expression of different inflammatory factors can either promote or counteract neurodegenerative processes. Since many inflammatory responses are beneficial, directing and instructing the inflammatory machinery may be a better therapeutic objective than suppressing it.

Signals from the X: signal transduction and X-linked mental retardation

The dramatic increase in genomic information is allowing the rapid identification of genes that are altered in mental retardation (MR). It is necessary to place their resulting gene products in their cellular context to understand how they may have contributed to a patient's cognitive deficits. This review will consider signaling molecules that have been implicated in X-linked MR and the known pathways by which these proteins covey information will be delineated. The proteins discussed include four distinct classes: transmembrane receptors, guanine nucleotide related proteins, kinases, and translational regulators.