Caspase-3-Mediated Apoptosis of Human Eosinophils by the Tissue-Invading Helminth <i>Paragonimus westermani</i>

Abstract

Background: Eosinophils are important cells in host immunity to infections by parasitic worms. Tissue-invasive helminthic parasites have been known to induce apoptosis of immune cells for their successful establishment in vivo. We have previously found that high doses of excretory-secreted products (ESP) secreted by lung fluke Paragonimus westermani newly excysted metacercariae (PwNEM), which cause pulmonary or extrapulmonary paragonimiasis in human beings, accelerate eosinophil cell death. However, little is known about the mechanism of eosinophil apoptosis induced by the Paragonimus-derived products. Objective: We examined involvement of caspase 3 activation in eosinophil cell death induced by ESP produced by PwNEM. Methods: Eosinophils were isolated from the peripheral blood of healthy donors by CD16-negative immunomagnetic selection. We examined the inhibitory effect of pan-caspase inhibitor on ESP-triggered phosphatidylserine (PS) externalization on the outer surface of eosinophils and intracellular activation of caspase 3 in cell lysates treated with the ESP. Results: When ESP secreted by PwNEM were incubated for up to 3 h with eosinophils, they increased surface exposure of PS on eosinophils in a time- and dose-dependent manner. This proapoptotic effect of the ESP on eosinophils was significantly inhibited by pretreatment of cells with pan-caspase inhibitor z-VAD-fmk, and was completely abolished by heat inactivation of ESP at 56°C. The activated forms of caspase 3 were also clearly detected in eosinophils incubated with ESP. Moreover, ESP potently inhibited prolonged survival of eosinophils induced by cytokines such as IL-5, IL-3, and GM-CSF. Conclusion: These results suggest that ESP secreted by PwNEM contain biological active factors causing caspase-3-mediated apoptosis of human eosinophils, thereby enabling the larvae to evade and to subvert the tackle by eosinophils during the early phase of the infection.

A 27 kDa Cysteine Protease Secreted by Newly Excysted Paragonimus westermani Metacercariae Induces Superoxide Anion Production and Degranulation of Human Eosinophils

“…The ESP produced by PwNEM was recently found to rapidly induce a direct time-and concentration-dependent increase in the rate of constitutive apoptosis in normal human eosinophils [16]. Moreover, eosinophil apoptosis by the ESP was shown to be mediated by activation of caspase-3 [17]. In addition, we observed that 10 μ g/ ml of the 27 kDa CP rapidly induced phosphatidylserine externalization on the cell surface of human eosinophils (data not shown).…”

Decrease of peritoneal inflammatory CD4+, CD8+, CD19+ lymphocytes and apoptosis of eosinophils in a murine Taenia crassiceps infection

“…In our experiments, we found an increase in caspase-3 activity in peritoneal cells from infected mice at several time points after infection. Likewise, Min et al (2004) reported activated caspase 3 in eosinophils incubated with Paragonimus westermani excretory-secretory products. In these cells, we also observed chromatin condensation, strangling, and nuclear fragmentation by performing electron microscopy studies Fig.…”

North American Paragonimiasis (Caused by Paragonimus kellicotti ) in the Context of Global Paragonimiasis

“…The parasite produces products that result in what has been termed "a zone of immune privilege" (17,116). This occurs, in part, as the result of the action of 27-and 28-kDa enzymes released from the parasite that cleave human immunoglobulin G (IgG) (17,42).…”

“…The degradation of IgG in turn results in the diminution of IgG-induced eosinophil degranulation and production/release of superoxide (160). Eosinophils become apoptotic in response to worm excretory/ secretory products, which in turn results in a substantial downregulation of the local inflammatory response (116).…”