Modulation of HLA-G expression in human neural cells after neurotropic viral infections.

HLA-G is a nonclassical human major histocompatibility complex class I molecule. It may promote tolerance, leading to acceptance of the semiallogeneic fetus and tumor immune escape. We show here that two viruses-herpes simplex virus type 1 (HSV-1), a neuronotropic virus inducing acute infection and neuron latency; and rabies virus (RABV), a neuronotropic virus triggering acute neuron infection-upregulate the neuronal expression of several HLA-G isoforms, including HLA-G1 and HLA-G5, the two main biologically active isoforms. RABV induces mostly HLA-G1, and HSV-1 induces mostly HLA-G3 and HLA-G5. HLA-G expression is upregulated in infected cells and neighboring uninfected cells. Soluble mediators, such as beta interferon (IFN-beta) and IFN-gamma, upregulate HLA-G expression in uninfected cells. The membrane-bound HLA-G1 isoform was detected on the surface of cultured RABV-infected neurons but not on the surface of HSV-1-infected cells. Thus, neuronotropic viruses that escape the host immune response totally (RABV) or partially (HSV-1) regulate HLA-G expression on human neuronal cells differentially. HLA-G may therefore be involved in the escape of certain viruses from the immune response in the nervous system.

Evidence of a role for Munc18-2 and microtubules in mast cell granule exocytosis.

Compound exocytosis of inflammatory mediators from mast cells requires SNARE and a series of accessory proteins. However, the molecular steps that regulate secretory granule movement and membrane fusion as well as the role of the cytoskeleton are still poorly understood. Here, we report on our investigation of the role of syntaxin-binding Munc18 isoforms and the microtubule network in this process. We found that mast cells express Munc18-2, which interacts with target SNAREs syntaxin 2 or 3, as well as Munc18-3, which interacts with syntaxin 4. Munc18-2 was localised to secretory granules, whereas Munc18-3 was found on the plasma membrane. Increased expression of Munc18-2 and derived peptides containing an interfering effector loop inhibited IgE-triggered exocytosis, while increased expression of Munc18-3 showed no effect. Munc18-2 localisation on granules is polarised; however, upon stimulation Munc18-2 redistributed into forming lamellipodia and persisted on granules that were aligned along microtubules, but was excluded from F-actin ruffles. Disruption of the microtubule network with nocodazole provoked Munc18-2 redistribution and affected mediator release. These findings suggest a role for Munc18-2 and the microtubule network in the regulation of secretory granule dynamics in mast cells.

SNAREs and associated regulators in the control of exocytosis in the RBL-2H3 mast cell line.

Mast cells participate in inflammation and allergies by releasing biologically active mediators stored in numerous cytoplasmic granules. Degranulation is tightly controlled and requires activation of cell surface receptors, such as the high affinity IgE receptor (FcepsilonRI). Here, we discuss some of the key components of the molecular machinery that regulates the final steps of fusion between the granular and plasma membrane based on results obtained with the rat mast cell line RBL-2H3. We emphasize the role of soluble N-ethylmaleimide attachment protein receptors (SNAREs) proteins such as syntaxin 4 that can promote membrane fusion through formation of a stable complex with SNAP-23. We also highlight the role of a Ser/Thr kinase found to be associated with Rab3D, a negative regulator of degranulation. Associated kinase activity, which diminishes after stimulation as a consequence of intracellular calcium increases, specifically phosphorylates syntaxin 4 thereby affecting its capacity to bind to its t-SNARE partner SNAP-23. Our results suggest a new way of how Rab3 GTPases may intersect with the function of SNAREs thought to be universal mediators of membrane fusion.

Immunoregulatory properties of mast cell-derived exosomes.

Transmission of information from mast cells to neighboring or distant cells must be established continuously in order to ensure homeostasis or to initiate immune and inflammatory responses. Owing to their strategic location in peripheral tissues and their prompt response to various stimuli, mast cells can be considered as the cell prototype to fulfill such a sentinel function. There are several ways for mast cells to communicate with other cells including cell-cell interactions via membrane-associated receptors, cytokines and other soluble mediators, and a newly described messenger which consists of membrane vesicles called exosomes carrying a number of immunoregulatory molecules.

Immunoreactive Calcitonin Gene-Related Peptide, Vasoactive Intestinal Polypeptide, and Somatostatin in Developing Chicken Spinal Cord Motoneurons.

The distribution of calcitonin gene-related peptide (CGRP)-, vasoactive intestinal polypeptide (VIP)-, and somatostatin (SOM)-like immunoreactivities (-LI) in neurons of the spinal cord of developing chickens was characterized by use of the indirect immunofluorescence technique, and the findings related to a possible role for these peptides in the development of muscles and motor endplates. CGRP-LI in presumptive motoneurons of the ventral horn was first observed at embryonic day 6. During the following days the number of CGRP-immunoreactive (IR) cells increased reaching high numbers between days 12 and 18 of incubation, and thereafter decreasing in numbers until hatching. SOM-LI was first observed on embryonic day 7, while VIP-LI appeared on days 12 - 13. The number of SOM- and VIP-IR cells was considerably lower than that observed for CGRP-LI, but they also exhibited an initial increase followed by a decrease towards hatching. Intrathecal administration of colchicine increased the number of CGRP-IR motoneurons at days 7 and 30 after hatching and of VIP-IR ones at day 7, while at day 30 no expression of VIP-LI was found. Colchicine treatment did not cause any significant change in the number of SOM-IR motoneurons after hatching. The effect of VIP, SOM, and CGRP on cAMP accumulation in primary cultures of chick muscle cells was determined after labelling of the cells by (2-3H) adenine and by radioimmunoassay. All three peptides stimulated the accumulation of cAMP. However, the development of the pharmacological response of each of the peptides followed a different time course during in vitro differentiation of the primary cultures. The response of CGRP was the latest to develop and did not significantly decrease after the maximal response had been reached around day 3. The data are discussed in terms of 'trophic' effects of these neuropeptides upon muscle and spinal cord differentiation and synaptogenesis.