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Biomedical subjects

H U Simon

Publications and source records attributed to H U Simon.

At least 19 recordsLinked to original sources
PubMed1999

Skin homing (cutaneous lymphocyte-associated antigen-positive) CD8+ T cells respond to superantigen and contribute to eosinophilia and IgE production in atopic dermatitis.

In allergic inflammations of the skin, activation of CD4+ T cells was demonstrated to play an important role; however, a minor role for CD8+ T cells is implied. In the present study, we compared cutaneous lymphocyte-associated Ag (CLA)-expressing CD4+ and CD8+ subsets, which were isolated from peripheral blood and lesional skin biopsies in atopic dermatitis (AD) patients. We demonstrated that CD8+CLA+ T cells proliferate in response to superantigen and are as potent as CD4+CLA+ T cells in IgE induction and support of eosinophil survival. In atopic skin inflammation, the existence of high numbers of CD4+ and CD8+ T cells was demonstrated by immunohistochemistry and by culturing T cells from skin biopsies. In peripheral blood, both CD4+ and CD8+ subsets of CLA+CD45RO+ T cells were in an activated state in AD. The in vivo-activated CLA+ T cells of both subsets spontaneously released an IL-5- and IL-13-dominated Th2 type cytokine pattern. This was confirmed by intracytoplasmic cytokine staining immediately after isolation of the cells from peripheral blood. In consequence, both CD4+ and CD8+, CLA+ memory/effector T cells induced IgE production by B cells mainly by IL-13, and enhanced eosinophil survival in vitro by delaying eosinophil apoptosis, mainly by IL-5. These results indicate that in addition to the CD4+ subset, the CD8+CLA+ memory/effector T cells are capable of responding to superantigenic stimulation and play an important role in the pathogenesis of AD.

Adult↗
PubMed1998

Role for Bcl-xL in delayed eosinophil apoptosis mediated by granulocyte-macrophage colony-stimulating factor and interleukin-5.

Eosinophils are potent inflammatory cells involved in allergic reactions. Inhibition of apoptosis of purified eosinophils by certain cytokines has been previously shown to be an important mechanism causing tissue eosinophilia. To elucidate the role of Bcl-2 family members in the inhibition of eosinophil apoptosis, we examined the expression of the known anti-apoptotic genes Bcl-2, Bcl-xL, and A1, as well as Bax and Bcl-xS, which promote apoptosis in other systems. We show herein that freshly isolated human eosinophils express significant amounts of Bcl-xL and Bax, but only little or no Bcl-2, Bcl-xS, or A1. As assessed by reverse transcription-polymerase chain reaction, immunoblotting, flow cytometry, and immunocytochemistry, we show that spontaneous eosinophil apoptosis is associated with a decrease in Bcl-xL mRNA and protein levels. In contrast, stimulation of the cells with granulocyte-macrophage colony-stimulating factor (GM-CSF) or interleukin-5 (IL-5) results in maintenance or upregulation of Bcl-xL mRNA and protein levels. Moreover, Bcl-2 protein is not induced by GM-CSF or IL-5 in purified eosinophils. Bcl-2 protein is also not expressed in tissue eosinophils as assessed by immunohistochemistry using two different eosinophilic tissue models. Furthermore, Bcl-xL antisense but not scrambled phosphorothioate oligodeoxynucleotides can partially block the cytokine-mediated rescue of apoptotic death in these cells. These data suggest that Bcl-xL acts as an anti-apoptotic molecule in eosinophils.

Apoptosis↗
PubMed1998

Role for tyrosine phosphorylation and Lyn tyrosine kinase in fas receptor-mediated apoptosis in eosinophils.

Fas ligand/Fas receptor molecular interactions have been implicated as having an important function for the regulation of eosinophil apoptosis. The purpose of the present study was to investigate biochemical events triggered by the engagement of the Fas receptor in freshly isolated human and mouse eosinophils. Activation of the Fas receptor on eosinophils with the agonistic anti-Fas monoclonal antibody (MoAb) resulted in increased tyrosine phosphorylation of several intracellular proteins. The tyrosine kinase inhibitors lavendustin A and genistein inhibited Fas receptor-induced cell death in both human and mouse eosinophils in vitro and prevented, at least partially, Fas receptor-mediated resolution of eosinophilic inflammation in a mouse in vivo model of lung eosinophilia. In addition, in freshly purified human eosinophils, lavendustin A prevented anti-Fas MoAb-induced proteolytic cleavage of lamin B, suggesting that tyrosine kinases may amplify the proteolytic signaling cascade within interleukin-1beta converting enzyme (ICE) family proteases. Moreover, the tyrosine kinase Lyn was identified as being involved in Fas receptor-mediated cell death. Collectively, these results demonstrate that tyrosine phosphorylation is an important step in the generation of the Fas receptor-linked transmembrane death signal in eosinophils and that Lyn participates in this pathway.

Animals↗
PubMed1998

Disruption of fas receptor signaling by nitric oxide in eosinophils.

It has been suggested that Fas ligand-Fas receptor interactions are involved in the regulation of eosinophil apoptosis and that dysfunctions in this system could contribute to the accumulation of these cells in allergic and asthmatic diseases. Here, we demonstrate that nitric oxide (NO) specifically prevents Fas receptor-mediated apoptosis in freshly isolated human eosinophils. In contrast, rapid acceleration of eosinophil apoptosis by activation of the Fas receptor occurs in the presence of eosinophil hematopoietins. Analysis of the intracellular mechanisms revealed that NO disrupts Fas receptor-mediated signaling events at the level of, or proximal to, Jun kinase (JNK), but distal to sphingomyelinase (SMase) activation and ceramide generation. In addition, activation of SMase occurs downstream of an interleukin 1 converting enzyme-like (ICE-like) protease(s) that is not blocked by NO. However, NO prevents activation of a protease that targets lamin B1. These findings suggest a role for an additional NO-sensitive apoptotic signaling pathway that amplifies the proteolytic cascade initialized by activation of the Fas receptor. Therefore, NO concentrations within allergic inflammatory sites may be important in determining whether an eosinophil survives or undergoes apoptosis upon Fas ligand stimulation.

Apoptosis↗
PubMed1998

Early-onset and adult periodontitis associated with abnormal cytokine production by activated T lymphocytes.

There is growing evidence for an important role of the immune system in the pathogenesis of periodontitis. To further characterize the possible immunoregulatory dysfunction of peripheral blood mononuclear cells (PBMC) in periodontitis patients, we investigated functional aspects of PBMC from patients with early-onset periodontitis (EOP) and adult periodontitis (AP). Compared to controls, we observed decreased proliferative responses of PBMC from patients with EOP following stimulation with a mitogenic stimulus (phytohemagglutinin). To investigate whether this abnormality reflects a modulation in cytokine production, we measured the in vitro production of interleukin (IL)-3, IL-5, granulocyte macrophage colony-stimulating factor (GM-CSF), and interferon-gamma (IFN-gamma) by activated PBMC. PBMC in EOP patients expressed significantly decreased levels of IFN-gamma protein in response to mitogenic stimulation. Reduced IFN-gamma secretion was associated with decreased IFN-gamma and IL-2 mRNA expression in these cells, as well as decreased HLA-DR surface expression on monocytes. On the other hand, we observed significantly higher levels of IL-5 and GM-CSF in the same system using PBMC from AP patients. These were comparable to the levels observed for patients with allergic asthma. These data imply that EOP is associated with decreased Th1-like cytokine expression, and that the PBMC response from patients with AP is predominantly Th2/Th0 in nature.

Adolescent↗
PubMed1997

[Significance of delayed eosinophilic apoptosis in chronic allergic inflammations].

Eosinophils are potent inflammatory cells involved in allergic reactions. Recent studies suggest that delayed eosinophil apoptosis is a pathogenic event for the accumulation of these cells in chronic eosinophilic inflammation. Therefore, it is important to study the mechanisms which regulate eosinophil apoptosis. Such knowledge may help to identify useful targets for the development of new drugs. Here we review recent progress in our understanding of the processes regulating eosinophil apoptosis.

Apoptosis↗
PubMed1997

Defective TCR stimulation in anergized type 2 T helper cells correlates with abrogated p56(lck) and ZAP-70 tyrosine kinase activities.

Development of IgE-mediated allergic conditions is dependent on the secretion of a Th2 cytokine pattern, including IL-4, IL-5, and IL-13. The induction of anergy would be one mechanism to abrogate cytokine secretion by Th2 cells, which may be pivotal to the allergic response. We demonstrate here that incubation of cloned human CD4+ phospholipase A2 (PLA)-specific Th2 cells with antigenic peptide, in the absence of professional APC, results in a state of nonresponsiveness. The anergic T cells failed to proliferate or secrete IL-4 in response to optimal stimulation with PLA and autologous, professional APC. Secretion of IL-5 and IL-13, however, was only partially inhibited. The anergic state of the Th2 cells was not associated with CD3 or CD28 down-regulation. However, anergy did appear to be closely related to alterations in signaling pathways, mediated through the TCR, of the cells. In contrast to untreated Th2 cells, anergized Th2 cells failed to respond to anti-CD3 mAb with either increased tyrosine kinase activity or increased levels of tyrosine phosphorylation of p56(lck) or ZAP70. A strong and sustained intracellular calcium flux, observed in untreated Th2 cells in response to anti-CD3 mAb, was absent in anergic Th2 cells. Furthermore, the induction of anergy seems to represent an active process, associated with increased levels of basal tyrosine kinase activity, cytokine production, and CD25 up-regulation in anergic Th2 cells. Together, our results indicate that anergy in Th2 cells is associated with defective transmembrane signaling through the TCR.

Antigen Presentation↗
PubMed1997

Direct demonstration of delayed eosinophil apoptosis as a mechanism causing tissue eosinophilia.

Nasal polyps, which often occur in association with allergic rhinitis and asthma, are characterized by a marked infiltration of eosinophils. Using a method for detecting eosinophils with DNA strand breaks, we found direct evidence for inhibition of eosinophil apoptosis in this model of tissue eosinophilia. By using Southern blot analysis linked to reverse transcription-PCR, we detected a mRNA signal specific for IL-5 in all nasal polyps. The identification of IL-5 as a major eosinophil survival factor was confirmed by ELISA measurements using tissue homogenates. Moreover, immunohistochemical analysis of the nasal polyp tissues demonstrated that IL-5 was localized in lymphocytes, mast cells, and eosinophils. Treatment of the eosinophil-infiltrated tissue with neutralizing anti-IL-5 mAb induced eosinophil apoptosis and decreased tissue eosinophilia. Therefore, IL-5 may represent an important cytokine responsible for the delay of the death process in eosinophils in nasal polyps. In addition, a previously suggested IL-4-dependent specific recruitment of eosinophils into the inflamed tissue could be excluded by our studies. Taken together, these findings suggest a novel mechanism by which eosinophils specifically accumulate in pathologic human tissues.

Apoptosis↗
PubMed1997

Anti-apoptotic signals of granulocyte-macrophage colony-stimulating factor are transduced via Jak2 tyrosine kinase in eosinophils.

Cytokine-mediated inhibition of eosinophil apoptosis is a mechanism causing tissue eosinophilia. Previously published work suggested that activation of the Lyn-Ras-Raf-1-MAP kinase pathway is obligatory for prevention of eosinophil apoptosis by eosinophil hematopoietins. We demonstrate herein that activation of freshly isolated human blood eosinophils by granulocyte-macrophage colony-stimulating factor (GM-CSF) is associated with increased tyrosine phosphorylation of Jak2. The tyrosine kinase blocker, tyrphostin B42, prevented activation of Jak2 but not Lyn, suggesting that Jak2 is the specific target for tyrphostin B42 in eosinophils. In addition, since Lyn remained unaffected by tyrphostin B42, it is unlikely that Jak2 is required for Lyn activation in this model. To test whether tyrosine phosphorylation of Jak2 is linked to GM-CSF-mediated prolonged eosinophil survival, we determined the effect of tyrphostin B42 on eosinophil viability and apoptosis. Prevention of Jak2 activation by tyrphostin B42 was associated with the inability of GM-CSF to prevent eosinophil apoptosis. These data suggest that disruption of not only the Lyn-Ras-Raf-1-MAP kinase but also the Jak-STAT pathway blocks the ability of eosinophil survival factors to prevent apoptosis in eosinophils.

Apoptosis↗