Reed, Charles E.

Abstract Human eosinophils have been reported to express both the mRNA and protein for the high affinity IgE receptor (FcεRI); it is speculated that this receptor plays a role in eosinophil mediator release in allergic diseases. However, questions still remain. How much of the FcεRI protein is actually expressed on the cell surface of the eosinophil? If they are present, are these IgE receptors associated with effector functions of eosinophils? To address these issues, we studied blood eosinophils from patients with ragweed hay fever. A high level of low affinity IgG receptor (FcγRII, CD32), but no expression of FcεRI, was detectable on the eosinophil surface by standard FACS analysis. However, after in vitro sensitization with biotinylated chimeric IgE (cIgE), cell-bound cIgE was detected by PE-conjugated streptavidin. This cIgE binding was partially inhibited by anti-FcεRI mAb, suggesting that eosinophils do express minimal amounts of FcεRI detectable only by a sensitive method. Indeed, FACS analysis of whole blood showed that eosinophils express ∼0.5% of the FcεRI that basophils express. When stimulated with human IgE or anti-human IgE, these eosinophils did not exert effector functions; there was neither production of leukotriene C4 or superoxide anion nor any detectable degranulation response. In contrast, eosinophils possessed membrane-bound human IgG and showed functional responses when stimulated with human IgG or anti-human IgG. Thus, IgG and/or cytokines, such as IL-5, appear to be more important for eosinophil activation in allergic diseases than IgE.

Abstract To determine the histologic differences in the airways of patients who died from sudden-onset asthma and the more common slow-onset asthma, we studied seven cases of fatal asthma. The numbers of eosinophilsand neutrophils, as well as extracellular deposition of their respective granule contents in the airway mucosa and submucosa, were determined and statistically analyzed. Four of the seven patients had slow-onset asthma attacks in which the time interval between onset of asthma and death was more than 2.5 h. In contrast, three patients had sudden-onset asthma in which the time interval between onset of asthma attack and death was less than 1 h. The four patients with slow-onset fatal asthma had more eosinophils (34.1 ± 6.3 in slow-onset; 9.7 ± 3.5 in sudden-onset; p = 0.002) and fewer neutrophils (4.8 ± 2.0 in slow-onset; 16.8 ± 5.4 in sudden-onset; p = 0.008) in the airway submucosa than did patients with sudden-onset fatal asthma. In addition, within the slow-onset fatal asthma group, eosinophils exceeded neutrophils in the airway submucosa (eosinophils > neutrophils, p = 0.002). By contrast, within the sudden-onset fatal asthma group, neutrophils exceeded eosinophils (neutrophils > eosinophils, p = 0.04). We suggest that sudden-onset fatal asthma is immunohistologically distinct from slow-onset fatal asthma and that it is characterized by a relative paucity of eosinophils in the face of an excess of neutrophils in the airway submucosa. These observations raise the possibility that the mechanism of airway inflammation as well as that of airway narrowing in sudden-onset fatal asthma may be quite distinct from those in slow-onset fatal asthma.