Glucocorticoids can down-regulate many inflammatory and immune responses and constitute a powerful therapeutic tool in a number of diseases. However, they have a somewhat paradoxical effect on neutrophils, in that they prolong their survival. Because leukotriene B4 (LTB4) can also extend neutrophil survival, we proposed that glucocorticoids could prevent neutrophil apoptosis by up-regulating their expression of the high-affinity LTB4 receptor (BLT1). Here we show that, indeed, dexamethasone (DEX) up-regulates the steady-state levels of BLT1 mRNA in human neutrophils. The effect was time and concentration dependent, being maximal at 4 h and at 10–100 nM DEX. The effect was also dependent on transcriptional activity, whereas BLT1 mRNA stability was not affected. DEX-induced up-regulation of BLT1 expression was prevented by pretreatment with the LTB4 antagonist LY255283. Moreover, LTB4 itself up-regulated the expression of BLT1 mRNA. BLT1 protein expression on neutrophils exposed to DEX for 24 h was also up-regulated 2- to 3-fold, and DEX-treated as well as LTB4-treated cells showed enhanced responsiveness to LTB4 in terms of intracellular Ca2+ mobilization and chemotaxis. Whereas DEX and LTB4 alone decreased neutrophil apoptosis by ∼50%, neutrophils treated with both LTB4 and DEX showed >90% survival at 24 h. Moreover, BLT1 antagonists prevented the increased neutrophil survival induced by DEX as well as by LTB4. Taken together, our results suggest that DEX-induced up-regulation of BLT1 expression in neutrophils may be one mechanism through which glucocorticoids can prolong neutrophil survival, namely by enhancing cell responses to the antiapoptotic effect of LTB4.

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Th17 cells have been implicated in a number of inflammatory and autoimmune diseases. The phospholipid mediator platelet-activating factor (PAF) is found in increased concentrations in inflammatory lesions and has been shown to induce IL-6 production. We investigated whether PAF could affect the development of Th17 cells. Picomolar concentrations of PAF induced IL-23, IL-6, and IL-1β expression in monocyte-derived Langerhans cells (LCs) and in keratinocytes. Moreover, when LC were pretreated with PAF and then cocultured with anti-CD3- and anti-CD28-activated T cells, the latter developed a Th17 phenotype, with a significant increase in the expression of the transcriptional regulator RORγt and enhanced expression of IL-17, IL-21, and IL-22. PAF-induced Th17 development was prevented by the PAF receptor antagonist WEB2086 and by neutralizing antibodies to IL-23 and IL-6R. This may constitute a previously unknown stimulus for the development and persistence of inflammatory processes that could be amenable to pharmacologic intervention.

Phosphorylation on tyrosine residues is recognized as an important mechanism for connecting extracellular stimuli to cellular events and defines a variety of physiologic responses downstream of G protein-coupled receptor (GPCR) activation. To date, few protein tyrosine phosphatases (PTPs) have been shown to associate with GPCRs, and little is known about their role in GPCR signaling. To discover potential cysteinyl-leukotriene receptor (CysLT 1 R)-interacting proteins, we identified protein tyrosine phosphatase « (PTP«) in a yeast two-hybrid assay. Since both proteins are closely linked to asthma, we further investigated their association. Using a human embryonic kidney cell line 293 (HEK-293) cell line stably transfected with the receptor (HEK-LT1), as well as human primary monocytes, we found that PTP« colocalized with CysLT 1 R in both resting and leukotriene D4 (LTD 4 )stimulated cells. Cotransfection of HEK-LT1 with PTP« had no effect on CysLT 1 R expression or LTD 4 -induced internalization, but it inhibited LTD 4 -induced CXC chemokine 8 (CXCL8) promoter transactivation, protein expression, and secretion. Moreover, reduced phosphorylation of extracellular signal regulated kinase 1/2 (ERK1/2), but not of p38 or c-Jun-Nterminal kinase 1 or 2 mitogen-activated protein kinases (MAPKs), was observed upon LTD 4 stimulation of HEK-LT1 coexpressing cytosolic (cyt-) PTP«, but not receptor (R) PTP«. The increased interaction of cyt-PTP« and ERK1/2 after LTD 4 stimulation was shown by coimmunoprecipitation. In addition, enhanced ERK1/2 phosphorylation and CXCL8 secretion were found in LTD 4 -stimulated human monocytes transfected with PTP«-specific siRNAs, adding support to a regulatory/inhibitory role of PTP« in CysLT 1 R signaling. Given that the prevalence of severe asthma is increasing, the identification of PTP« as a new potential therapeutic target may be of interest.

Both therapies for Graves' disease (GD), radioactive iodine (RAI) and antithyroid drugs (ATD), were reported to have specific immune effects. We aimed at investigating the effects of RAI therapy on cellular subsets involved in immune regulation. We conducted a thirty day follow-up prospective cohort study of adult patients. Patients eligible for RAI therapy at our centre were approached. Twenty seven patients with GD were recruited, among whom 11 were treated with ATD. Twenty-two healthy subjects (HS) were also studied. Over time, frequency of regulatory T cells (Treg) and of invariant natural killer T cells (iNKT), along with Treg cell-mediated suppression and underlying mechanisms, were monitored in the peripheral blood. Variance in frequency of Treg and iNKT after RAI therapy was higher in GD patients than in HS over time (p < 0.0001). Reduced Treg suppressive function was observed after RAI therapy in GD patients (p = 0.002). ATD medication prior to RAI dampened these outcomes: less variation of Treg frequency (p = 0.0394), a trend toward less impaired Treg function, and prevention of reduced levels of suppressive cytokines (p < 0.05). Shortly after RAI therapy, alterations in immunoregulatory cells in patients with GD were observed and partially prevented by an ATD pretreatment. Worsening of autoimmunity after RAI was explained in previous studies by enhanced immune activity. This study adds new highlights on immune regulation deficiencies after therapeutic interventions in thyroid autoimmunity.