Slow-reacting substances and leukotrienes

Leukotriene D4-induced signal transduction

In a human epithelial cell line LTD4 induces a calcium signal that is dependent on both intracellular mobilization and influx of calcium. This calcium signal is generated via the activation of dual G protein pathways. Whereas the intracellular mobilization of calcium is regulated by a pertussis toxin-insensitive G protein, the subsequent influx of calcium is regulated by a pertussis toxin-sensitive G protein. Furthermore, a LTD4-induced cellular elevation of cAMP also participates in the regulation of this calcium signal. The increase in cAMP is directly related to the LTD4-induced influx of calcium, perhaps by an activation of protein kinase A and a subsequent phosphorylation of a plasma membrane channel. This model of the LTD4-induced signaling pathway in epithelial cells is outlined in Figure 2.

Postburn suppression of murine lymphocyte and neutrophil functions is not reversed by prostaglandin blockade

Certain arachidonic acid metabolites, including prostaglandins (PGs) E1 and E2, have been shown to exert marked immunosuppressive effects on T-cell and macrophage functions. Cyclooxygenase blockade with indomethacin or ibuprofen may ameloriate these effects. In the current study we measured lymphocyte proliferation by thymidine incorporation, the presence of T-cell activation antigens with monoclonal antibodies and two-color flow cytometry, and neutrophil (PMN) oxidative burst using a fluorescent marker, in control mice and in burned mice treated with indomethacin for 10 days after injury. One-half of the cell cultures were treated with indomethacin in vitro to ensure its continued presence during stimulation. Separate groups of mice were fed a fish oil-based diet which leads to the production of PGE3 rather than PGE2, versus standard mouse chow, a soy-bean oil-based diet which leads to PGE2 production. Lymphocyte proliferation, expression of T-cell activation antigens, and PMN oxidative burst remained depressed in burned mice treated with indomethacin in vivo (plus in vitro) and in those which received the fish oil-based diet, compared to control. Blockade of PG synthesis after murine burn injury by cyclooxygenase inhibition or alterations in the diet failed to restore T-lymphocyte activation or proliferation or to improve PMN oxidative burst. These data suggest that PGE2 alone does not explain the immunosuppression noted after burn injury.

Alterations of the host defense mechanism in burned patients

The host defense mechanism against microbial infection is seriously suppressed following a major thermal injury. In this article the specific and nonspecific systems are dissected, demonstrating known sites of alteration, and laying out a rational groundwork for future intervention.

Clofazimine-mediated stimulation of prostaglandin synthesis and free radical production as novel mechanisms of drug-induced immunosuppression

The effects of clofazamine (3-(p-chloroanilino)-10-(p-chlorophenyl)-2, 10-dihydro-2-(isopropylimino)-phenazine) at concentrations of 0.625-20 micrograms/ml on the mitogen-induced transformation, luminol-enhanced chemiluminescence, arachidonic acid metabolism and sulphydryl content of human mononuclear leucocytes (MNL) were investigated in vitro. The drug at all concentrations tested decreased MNL sulphydryl content and inhibited mitogen-induced transformation. Clofazimine increased the spontaneous luminol-enhanced chemiluminescence and activated the arachidonic acid cascade in MNL. The anti-oxidants ascorbic acid and cysteine and the prostaglandin (PG) synthesis inhibitor indomethacin were used individually and in combination to identify the primary mediators of the anti-proliferative effects of clofazimine on MNL. Combinations of an anti-oxidant with a PG synthesis inhibitor completely protected MNL from clofazimine mediated inhibition of mitogen-induced transformation. These results show that the anti-proliferative activity of clofazimine is related to both the pro-oxidative and PG synthesis enhancing effects of the drug on MNL.