Di Capite Joseph, Shirley Anna, Nelson Charmaine, Bates Grant, Parekh Anant B
Department of Physiology, Anatomy and Genetics, University of Oxford, Parks Road, Oxford OX1 3PT, UK.
FASEB J. 2009 Mar;23(3):894-905. doi: 10.1096/fj.08-118935. Epub 2008 Oct 31.
Mast cells are key components of the immune system, where they help orchestrate the inflammatory response. Aberrant mast cell activation is linked to a variety of allergic diseases, including asthma, eczema, rhinitis, and nasal polyposis, which in combination affect up to 20% of the population in industrialized countries. On activation, mast cells release a variety of signals that target the bronchi and vasculature and recruit other immune cells to the inflammatory site. Prominent among such signals are the cysteinyl leukotrienes, a family of potent proinflammatory lipid mediators comprising leukotriene C(4) (LTC(4)), LTD(4), and LTE(4). LTC(4), the parent compound, is secreted from mast cells following Ca(2+) influx through store-operated calcium release-activated calcium (CRAC) channels. Here, we show that activated mast cells release a paracrine signal that evokes Ca(2+) signals in spatially separate resting mast cells. The paracrine signal was identified as a cysteinyl leukotriene because 1) RNAi knockdown or pharmacological block of the 5-lipoxygenase enzyme prevented activated mast cells from stimulating resting cells. 2) Block of cysteinyl leukotriene type I receptors on resting mast cells with the clinically prescribed receptor antagonist montelukast prevented their activation by active mast cells. 3) RNAi knockdown of cysteinyl leukotriene type I receptors on resting cells prevented them from responding to the paracrine signal derived from activated mast cells. 4) Purified LTC(4) evoked Ca(2+) signals in mast cells that were identical to those triggered by the paracrine signal. Low levels of stimulus intensity released sufficient levels of leukotriene to activate resting cells. Leukotriene secretion still occurred tens of minutes after stimulation, suggesting a role as a long-lasting trigger in mast cell activation. Stimulation of the cysteinyl leukotriene receptor activated CRAC channels and evoked prominent store-operated Ca(2+) entry. This resulted in further cysteinyl leukotriene production, triggering a positive feedback cascade. Acutely isolated mast cells from patients with allergic rhinitis exhibited store-operated Ca(2+) influx through CRAC channels and responded to cysteinyl leukotrienes. Histological analysis of samples taken from patients revealed clustering of mast cells, often located within 20 microm of each other, a distance sufficient for paracrine signaling by leukotrienes to operate effectively. We conclude that a positive-feedback cascade involving CRAC channels and cysteinyl leukotrienes constitute a novel mechanism for sustaining mast cell activation.
肥大细胞是免疫系统的关键组成部分，在其中协助协调炎症反应。肥大细胞的异常激活与多种过敏性疾病相关，包括哮喘、湿疹、鼻炎和鼻息肉病，在工业化国家，这些疾病加起来影响着高达20%的人口。激活后，肥大细胞释放多种信号，这些信号作用于支气管和脉管系统，并招募其他免疫细胞至炎症部位。这类信号中突出的是半胱氨酰白三烯，它是一类强效促炎脂质介质，包括白三烯C4（LTC4）、LTD4和LTE4。母体化合物LTC4是在钙离子通过储存性钙释放激活钙（CRAC）通道内流后从肥大细胞分泌的。在此，我们表明激活的肥大细胞释放一种旁分泌信号，该信号能在空间上分离的静息肥大细胞中引发钙离子信号。该旁分泌信号被鉴定为半胱氨酰白三烯，因为：1）RNA干扰敲低或5-脂氧合酶的药理学阻断可防止激活的肥大细胞刺激静息细胞。2）用临床处方的受体拮抗剂孟鲁司特阻断静息肥大细胞上的半胱氨酰白三烯I型受体，可防止其被激活的肥大细胞激活。3）RNA干扰敲低静息细胞上的半胱氨酰白三烯I型受体可防止它们对源自激活的肥大细胞的旁分泌信号作出反应。4）纯化的LTC4在肥大细胞中引发的钙离子信号与旁分泌信号触发的信号相同。低水平的刺激强度释放出足以激活静息细胞的白三烯水平。刺激后数十分钟仍有白三烯分泌，这表明其在肥大细胞激活中起持久触发作用。对半胱氨酰白三烯受体的刺激激活了CRAC通道并引发显著的储存性钙离子内流。这导致进一步产生半胱氨酰白三烯，触发正反馈级联反应。从过敏性鼻炎患者中急性分离的肥大细胞表现出通过CRAC通道的储存性钙离子内流，并对半胱氨酰白三烯作出反应。对患者样本的组织学分析显示肥大细胞聚集，它们通常彼此相距在20微米以内，这一距离足以使白三烯通过旁分泌信号有效地发挥作用。我们得出结论，涉及CRAC通道和半胱氨酰白三烯的正反馈级联反应构成了维持肥大细胞激活的一种新机制。
