Granulocytes, including neutrophils, eosinophils, and basophils, are important effector cells in the innate immune response against bacterial, fungal, and parasitic pathogens. Because granulocytes are terminally differentiated cells, the accumulations of granulocytes at sites of inflammation are determined by cell migration and delay/suppressed apoptosis. These processes are believed to be predominantly regulated by cytokines. G-CSF and GM-CSF are important surviving factors for neutrophils and IL-5 is associated with increased survival of eosinophils (Simon, 2001, 2003).
A small fraction of neutrophils is found to constitutively express CD137 (Simon, 2001). Eosinophils isolated from a healthy donor do not express CD137
(Simon, 2001). There is no report as of now regarding the expression of CD137 on basophils. CD137 expression on eosinophils could be observed in patients suffering from IgE-mediated allergic responses, but not in normal subjects or those patients suffering from non-IgE-mediated eosinophilic disorders (Heinisch et al., 2001). In both neutrophils and eosinophils, CD137 stimulation promoted apopto-sis in these cells, even in the presence of GM-CSF and/or IL-5 survival factors (Heinisch et al., 2000). In this regard, CD137 stimulation may play an important role in regulating granulocyte survival during the initiation and resolution of an inflammatory response. Combined with a report showing CD137 transcript that was frequently found in mast cells, a key type of cells storing and releasing inflammatory mediators for allergy, CD137 may also participate in the control of asthma induced by extrinsic allergens.
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If you suffer with asthma, you will no doubt be familiar with the uncomfortable sensations as your bronchial tubes begin to narrow and your muscles around them start to tighten. A sticky mucus known as phlegm begins to produce and increase within your bronchial tubes and you begin to wheeze, cough and struggle to breathe.