Eosinophil apoptosis

Dibbert B. Daigle I. Braun D. Schranz C, Weber M. Blaser K. Zangemeister-Wittke U. Akbar AN. Simon HU Role for Bcl-xL in delayed eosinophil apoptosis mediated by granulocyte-macrophage colony-stimulating factor and interleukin-5. Blood 1998 92 778-783. 

Simon, H. U., Yousefi, S., Schranz, C., Schapowal, A., Bachert, C., and Blaser, K., Direct demonstration of delayed eosinophil apoptosis as a mechanism causing tissue eosinophilia. J. Immunol. 158, 3902-3908 (1997). 

Meagher, L., Seckl, J.R. and Haslett, C. (1995). Opposing effects of glucocorticoids on neutrophil and eosinophil apoptosis. Submitted. 

Nth-terminal kinase (JNK) and p38 MAPK activity in eosinophils is regulated by caspases. Interestingly, the caspases involved are not the common apoptosis-related caspase-3 or -8, as is the case in other cells. The elucidation of the role of caspases in eosinophil apoptosis may thus facilitate the development of more specific and effective treatments for this type of allergic inflammation [69]. 

The xanthine theophylline has been used for several decades in the treatment of asthma. This compound produces different effects at the cellular level, including phosphodiesterase isoenzyme inhibition, adenosine antagonism, catecholamine secretion enhancement, and the modulation of calcium fluxes. Recently, theophylline was found to have both immunomodulatory and anti-inflammatory properties therefore, interest in its use in patients with asthma has been renewed [103]. Recent studies have thus discovered that at low doses, theophylline is able to decrease airway inflammation, accelerate eosinophil apoptosis, and decrease recruitment of lymphocytes and neutrophils to the lungs. Although it is classified as a phosphodiesterase inhibitor, its exact therapeutic mechanism of action remains undetermined [104]. Of the new mechanisms that have been included in the potential mode of action of theophylline, one is the apoptosis of inflammatory cells. In eosinophils and lymphocytes, for example, this effect is due to the compound s ability to inhibit phosphodiesterase, which leads to an even more pronounced increase in intracellular cAMP levels than that which occurs when adenylate cyclase, the enzyme that synthesizes cAMP, is activated. This inhibition and the resulting cAMP level increase thus lead to... 

Fig. 3. Th2 cells provide cytokines such as IL-4, IL-5, IL-9 and IL-13, which are essential for differentiation, survival and activity of basophils, mast cells and eosinophils. IL-4 and IL-13 induce IgE production from B cells. IL-5 induces eosinophils, increases eosinophil survival and reduces apoptosis. IL-9 stimulates mast cells. 

The effect of MAPK activation on cellular processes that affect cell function and the resulting pharmacology has been delineated using modem techniques such as knock-out cells and animals [1,3,6]. Activation of MAPK in inflammatory cells such as T-cells, B-cells, macrophages and eosinophils leads to expression and/or activation of pro-inflammatory genes and mediators such as interleukin-1(3 (IL-1(3), TNFa, IL-6, chemokines [e.g., IL-8, macrophage inflammatory factor-1 a, (3 (MIP-la,[3)J, MMPs and toxic molecules such as free radicals and nitric oxide [1,3]. These pro-inflammatory mediators induce cellular proliferation, differentiation, survival, apoptosis and tissue degradation/destruction and help induce chronic inflammation. Inhibition of any one or more of the MAPK family... 

Trautmann A, Schmid-Grendelmeier P, Kruger K, Crameri R, Akdis M, Akkaya A, et al T cells and eosinophils cooperate in the induction of bronchial epithelial apoptosis in asthma. J Allergy Clin Immunol 2002 109 329-337. 

Previous studies have reported that ERKs are characteristically associated with cell proliferation and protection from apoptosis (Bl, XI), while activation of JNK and p38 MAPK can promote apoptosis in many systems, including B lymphocytes (G5), cerebellar granule cells (K3), hematopoietic cells (K8), and neuronal cells (M3, XI). On the other hand, a recent report found that a pyridinyl imidazole, SB 202190, the specific inhibitor of p38 MAPK, by itself was sufficient to induce apoptosis in T lymphocyte Jurkat cells (N2). Moreover, Th-2-derived cytokine IL-5, the ERK activator and antiapoptotic factor for eosinophils, could also activate p38 MAPK in human eosinophils (BIO). We recently reported that cytokine IL-3, IL-5, and GM-CSF could prolong survival of human eosinophilic leukemic (EoL-1) cells through the transient activation of ERK (W15). On the other hand, activation of p38 MAPK in EoL-1 cells by the NSAID sodium salicylate (NaSal) could lead to apoptosis (W15). We also found that the suppression of ERK using ERK antisense phosphorothioate oligodeoxynucleotides could promote the apoptosis of peripheral blood eosinophils (W16). Moreover, we found that dexamethasone-induced apoptosis and activation of JNK and p38 MAPK activity in eosinophils are regulated by caspases (Z2). 

Fig. 3. Micrograph demonstrating die effect of NaSal on morphological changes in eosinophils (W16). After eosinophils were treated for 12 h (a) without or (b) with 20 mM NaSal, which is an apoptosis-inducing agent, cells were harvested and stained with Hemacolor Rapid blood smear staining set. The stained cells were examined by light microscopy. The arrows depict the apoptotic eosinophils...

Fig. 6. Apoptotic DNA ladder pattern of eosinophils treated with dexamethasone (Dexa, 2 (xM) for 18 h (Zl). DNA was extracted from cells with ethanol (P4) and electrophoresed on 1% agarose gel in 1 X TAE (Tris acetate-EDTA) buffer (pH 8.0). After electrophoresis, the gel was soaked in 1 x TAE buffer containing 0.5 /tg/ml ethidium bromide, and DNA was visualized by an ultraviolet illuminator. Reproduced with permission from Zhang, J. R, Wong, C. K., Lam, C. W. K., Ho, C. Y., and Hjelm, N. M., Biochemical assessment of apoptosis. Chinese J. Lab. Med. Clin. Sci. 1, 27-28 (2000).

Reproduced with permission from Zhang, J. R, Wong, C. K., and Lam, C. W. K. Role of caspases in dexamethasone-induced apoptosis and activation of c-Jun NH2-terminal kinase and p38 mitogen-activated protein kinase in human eosinophils. Clin. Exp. Immunol. 122,20-27 (2000) and Blackwell Science Ltd. 

Fig. 12. Effect of spontaneous apoptosis on the activation of caspase-3 in human eosinophils. Eosinophils (2 x 10 /ml) were cultured for 3 h. Cells were lysed and caspase-3 activity was measured by caspase-3 colorimetric assay kit (R D Systems). Enzymatic products were measured at 405 nm with BIOTEK EL340 ELISA microplate reader (BIO-TEK Instrument Inc., Vermont). Human recombinant caspase-3 (5 U) (Calbiochem, California) was used as a positive control. The stimulation index was determined by direct comparison to the level of the normal control. Background readings from cell lysates and buffers were substracted from the readings of both induced and uninduced samples samples before calculating the stimulation index in caspase-3 activity. The differences between control and treated groups were assessed by Student s i-test. P < 0.05 P < 0.001 (Z2).

A3 receptors are present on human eosinophils and couple to signalling pathways that lead to cell activation ( Kohno et al. 1996a Reeves et al. 2000). Despite this it has not proven easy to demonstrate the functional consequences of activation of these sites (Reeves et al. 2000). Nevertheless, the chronic inflammation in asthma is characterised by extensive infiltration of the airways by activated eosinophils (Holgate 1999 Pearlman 1999) and it remains possible that the elevated adenosine concentrations associated with asthma would contribute to eosinophil activation through stimulation of A3 receptors. In addition, it has been speculated that activation of A3 receptors may protect eosinophils from apoptosis (Gao et al. 2001). Thus, blockade of A3 receptors may reduce the numbers of eosinophils and their activation thereby reducing the pro-inflammatory burden in the lung. Consistent with this, following 6 weeks treatment of mild asthmatics with theophylline there was a... 

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