The inhibitory effect of dexamethasone on lymphocyte adhesion molecule expression and intercellular aggregation is not mediated by lipocortin 1

Glucocorticoids exert their anti-inflammatory activity through multiple pathways which include the inhibition of cell adhesion events. The glucocorticoid-induced protein lipocortin 1 (LC1) has reported anti-inflammatory properties and has been proposed as a putative mediator of the anti-inflammatory effects of glucocorticoids. The role of LC1 in mediating the glucocorticoid inhibition of lymphocyte adhesion and cell adhesion molecule (CAM) expression was investigated in vitro using a microaggregation assay, flow cytometry and confocal microscopy. Lymphocytes stimulated for 96 h with plastic-bound OKT3 antibody showed significant increases in LFA-1 and CD2 expression. Dexamethasone (DEX; 10−6m) inhibited this increase but the neutralizing anti-LC1 MoAb 1A (5 μg/ml) failed to reverse the DEX effect; neither was purified human LC1 (50 × 10−9m) able to inhibit CAM expression. The biological activity of the LC1 was confirmed by its ability to suppress monocyte phagocytosis and respiratory burst in response to bovine serum albumin (BSA)–anti-BSA complexes. OKT3 stimulation of cultured mononuclear cells resulted in intercellular aggregation, scored microscopically using a visual index. This aggregation was completely reversed by 10−6m DEX but unaffected by LC1 (50 × 10−9m). Significant intracellular expression of lymphocyte LC1 was observed using the anti-LC1 MoAb 1B in saponin-permeabilized cells. Distribution of LC1 had a diffuse, cytoplasmic pattern. LC1 expression was reduced following 3 h treatment with 10−6m DEX. These findings indicate that the DEX effects on lymphocyte adhesion and CAM expression are not mediated by LC1. Thus the reported in vivo effects of LC1 on leucocyte adhesion and transmigration probably occur through functional/conformation changes of surface CAM, rather than by alteration in expression

Lipocortin inhibition of extracellular and intracellular phospholipases A2 is substrate concentration dependent

Hydrolysis of Escherichia coli membrane phospholipids by pancreatic phospholipase A2 was inhibited by lipocortin from human monocytes in a substrate dependent manner. Inhibition was completely overcome at substrate concentrations above 250 μM. Lipocortin also inhibited partially purified preparations of two intracellular phospholipases A2, isolated from rat liver mitochondria and rat platelets when these enzymes were assayed at low micromolar concentrations of phosphatidylethanolamine. Inhibition gradually decreased with increasing substrate concentrations both for pancreatic and platelet phospholipase A2 and became completely abolished above 15 and 50 μM phosphatidylethanolamine, respectively

Involvement of interleukin-1, prostaglandins and mast cells in rectal distension-induced colonic water secretion in rats

In vivo rectal distension (RD) induces a neurally mediated colonic net water hypersecretion in rats. Interleukin-1β (IL-1β) also induces neural colonic water hypersecretion involving the release of prostaglandins (PGs) and a mast cell degranulation in rats. This study investigated in vivo the role of IL-1, PGs and mast cells in RD-induced colonic hypersecretion.Proximal colonic net water flux was determined using [14C]polyethylene glycol (PEG) 4000 (mol. wt, 4000) in anaesthetized rats. On strips taken from the distal colon: (i) a histological analysis was performed to determine the number of mucosal mast cells (MMC); and (ii) histamine levels were measured by radioimmunoassay after stimulation with compound 48/80.RD induced a net colonic water secretion that was blocked by i.c.v. administration of IL-1ra (an IL-1 receptor antagonist) and indomethacin, and by systemic treatment with doxantrazole and indomethacin. RD decreased the number of resident mast cells and the release of histamine from the distal colonic strips. Moreover, using SDS-PAGE immunoblotting the expression of IL-1β was detected in the brain.These results suggest that, in rats, RD induces colonic net water hypersecretion by the activation of a neuro-immunological reflex pathway, involving brain IL-1β, PG release and peripheral mast cell degranulation