To the Editor
Activated platelets are implicated in various clinical conditions. For example, soluble (s)P-selectin or platelet-derived microparticles have been detected in patients with diabetes mellitus, hypertension, hyperlipidemia and coronary artery diseases [Citation[1–3]]. In addition, activated platelets are implicated in thrombosis after percutaneous coronary intervention [Citation[3], Citation[4]]. However, to our knowledge, there have been few studies on the relationship between activated platelets and fiberoptic bronchoscopy (FOB). Complications associated with FOB examination sometimes occur. Most often these are due to tissue damages during the FOB procedure. We measured levels of soluble selectins in citrated plasma and evaluated platelet counts in the peripheral blood of 12 patients who had underwent FOB without any complications, because these factors are capable of causing the FOB-related proinflammatory process. Blood samples were collected from the patients before and after FOB.
Although platelet counts significantly decreased until 4 h after FOB (before FOB vs. 4 h after FOB; 221 ± 43 × 103/µl vs. 183 ± 39 × 103/µl, P < 0.01), they then increased at 24 h after FOB (207 ± 44 × 103/µl). In contrast, the serum levels of sP-selectin were significantly increased after FOB (before FOB vs. 24 h after FOB; 236 ± 65 vs. 314 ± 78 ng/ml, P < 0.01). However, the serum levels of sE-selectin and sL-selectin exhibited no significant changes.
The significant decrease of platelet counts after FOB may be due to consumption of platelets following focal tissue damage. When platelet activation and agglutination occur in the damaged area, the activated platelets release several cytokines and upregulate P-selectin [Citation[1], Citation[5], Citation[6]]. Um et al. Citation[7] reported that platelet activation and post-bronchoscopy fever occurred in relation to the severity of bleeding during FOB. In addition, it has been reported that sP-selectin is elevated in acute lung injury and after severe trauma [Citation[8], Citation[9]]. Our results accord with these previous reports. Some sP-selectins are generated from endothelial cells Citation[1]. On the other hand, increases in sE-selectin in the blood can be used to quantify endothelial activation Citation[10]. The lack of elevation of sE-selectin in the present study indicates minimal activation of the epithelium. Therefore, we consider that the elevation of sP-selectin after FOB was mainly released from platelets. The sP-selectin also could modulate leukocyte adhesion to the P-selectin expressed on platelets and endothelial cells Citation[1].
We conclude with the following hypotheses. The tissues and microvascular system receive damage during the FOB procedure and therefore platelet agglutination and activation occur. Several cytokines and chemokines are released from the activated platelets and up-regulate P-selectin in the damaged area. Leukocyte chemotaxis and migration into the damaged pulmonary region are subsequently induced, thus triggering the activation of other inflammatory cells. However, sP-selectin can inhibit the interaction between leukocytes and endothelial cells. The FOB procedure probably induces the proinflammatory process in most cases. Nevertheless, complications such as severe fever or pneumonia are rare. One of the reasons for this may be that sP-selectin plays an important role in blocking the excessive inflammation.
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