Evidence for presence of kynurenine in lung and brain of neonate hamsters

Kynurenine Pathway in Respiratory Diseases

The kynurenine pathway is the primary route for tryptophan catabolism and has received increasing attention as its association with inflammation and the immune system has become more apparent. This review provides a broad overview of the kynurenine pathway in respiratory diseases, from the initial observations to the characterization of the different cell types involved in the synthesis of kynurenine metabolites and the underlying immunoregulatory mechanisms. With a focus on respiratory infections, the various attempts to characterize the kynurenine/tryptophan (K/T) ratio as an inflammatory marker are reviewed. Its implication in chronic lung inflammation and its exacerbation by respiratory pathogens is also discussed. The emergence of preclinical interventional studies targeting the kynurenine pathway opens the way for the future development of new therapies.

T cell regulatory plasmacytoid dendritic cells expressing indoleamine 2,3 dioxygenase

Mature dendritic cells (DCs) are potent stimulators of T cells that recognize antigens presented by the DCs. In this chapter we describe mature DCs that suppress T cell responses to antigens they present due to expression of the intracellular enzyme indoleamine 2,3 dioxygenase (IDO). IDO-competent DCs are a subset of plasmacytoid DCs that can be induced to express IDO under certain inflammatory conditions in humans and mice. Though rare, IDO-expressing DCs acquire potent T cell suppressor activity that may predominate over the T cell stimulatory functions of all other antigen-presenting cells in physiologic environments due in part, to cooperation with regulatory T cells. Thus, IDO-expressing DCs are critical regulators of adaptive immunity that contribute to a wide range of inflammatory disease processes. As such, manipulating IDO expression in DCs using IDO inhibitors or IDO inducers offers considerable opportunities to improve immunotherapies in a range of clinically-significant disease syndromes.

The ependyma: a protective barrier between brain and cerebrospinal fluid

This review summarizes the current scientific literature concerning the ependymal lining of the cerebral ventricles of the brain with an emphasis on selective barrier function and protective roles for the common ependymal cell. Topics covered include the development, morphology, protein and enzyme expression including reactive changes, and pathology. Some cells lining the neural tube are committed at an early stage to becoming ependymal cells. They serve a secretory function and perhaps act as a cellular/axonal guidance system, particularly during fetal development. In the mature mammalian brain ependymal cells possess the structural and enzymatic characteristics necessary for scavenging and detoxifying a wide variety of substances in the CSF, thus forming a metabolic barrier at the brain-CSF interface.

In vitro effects of bladder mucosa and an enkephalinase inhibitor on tachykinin induced contractility of the dog bladder

Tachykinin-induced contractility of smooth muscle strips from dog bladders was studied in vitro, and the presence of substance P-like immunoreactivity and neurokinin A and neurokinin B-like immunoreactivity was examined in bladder sections. Nerve fibers with substance P-like immunoreactivity were present in the mucosa, submucosa and smooth muscle. Fibers were also found in nerves, intramural ganglia, and around blood vessels. Neurokinin A-like immunoreactivity had similar distribution, and no neurokinin B-like immunoreactivity was observed. Removal of the mucosa significantly enhanced the sensitivity and the maximum responses to the tachykinins. After removing the mucosa, the sensitivity to these tachykinins increased 0.4 to 0.5 log units (p less than 0.02). The responses to carbachol were not altered by mucosa removal. The leftward shifts of the concentration-response curves for neurokinin A were of similar magnitude after removal of the mucosa, and after pretreatment with phosphoramidon (10 microM), an enkephalinase inhibitor, in the presence of mucosa. However, phosphoramidon did not alter the sensitivity of the bladder strips to neurokinin B, and slightly changed the sensitivity to substance P (0.2 log units). Additional shifts of the substance P and neurokinin A curves to the left were observed in the presence of phosphoramidon when the mucosa was removed (0.6 and 0.5 log units, p less than 0.005). The order of potency for the tachykinins (neurokinin A greater than substance P) was not altered by mucosa removal, addition of phosphoramidon, or both. Neurokinin A was degraded by enkephalinase located in the bladder mucosa and addition of phosphoramidon or mucosa removal resulted in an inhibition or loss of enkephalinase activity. It is concluded that the responses to neurokinin A, which acts on NK-2 type of receptors, prevail on the dog bladder.

Asbestos-induced fibrosis in rats: increase in lung mast cells and autacoid contents

Adult male Wistar rats were treated with one tracheal instillation of 5 or 10 mg chrysotile B asbestos fibers in 0.5 ml saline, or 0.5 ml saline only (controls). Rats were killed at 1, 3, and 6 months postinstillation. Serotonin and histamine were quantitated in lung tissue homogenate using high-performance liquid chromatography with electrochemical and fluorometric detection, respectively. Serotonin was also quantitated in the cytoplasm of grouped (NEB) and individual (NEC) neuroendocrine cells and in mast cells using formaldehyde vapor-induced fluorescence and microspectrofluorometry, and density indices of NEBs, NECs, and mast cells were determined. Tissue edema, fibrotic lesions, and medial hypertrophy of pulmonary arterioles were assessed morphometrically. Test rats had higher pulmonary serotonin and histamine levels than controls at 1, 3, and 6 months. They also had higher cellular serotonin in NEBs at 1 month, but not in NECs, and tended to have higher serotonin levels in mast cells at 6 months. Mast cell numbers were higher among tests at 1 and 3 months, whereas NEBs and NECs were unchanged by asbestos. There was no difference between tests and controls in the amount of tissue edema at any time. However, all test rats had distinct lung lesions characterized by peribronchiolar fibrosis and bronchiolitis obliterans. No such lesions were present among control rats. Typically, mast cells were located immediately beneath the epithelial basal lamina of the bronchiolar fibrotic projections and at their stalks, whereas no mast cells were noted beneath normal epithelium, indicating a role of mast cells in asbestos-induced peribronchiolar fibrosis. Moreover, arteriolar medial hypertrophy at all three ages in conjunction with the increased levels of serotonin was an index of putative chronic pulmonary hypertension. Our results suggest that asbestos-induced rises in serotonin and histamine are due primarily to increased numbers of mast cells.