Airway Inflammation and Cellular Stress in Noneosinophilic Atopic Asthma: Research
Figure 2 shows the levels of inflammatory mediators. ECP, MPO, and IL-8 concentrations were detected in 100% of sputum supernatant samples, and GM-CSF concentrations were detected in 79% of sputum supernatant samples. Comparisons across the three groups revealed no difference in IL-8 and GM-CSF concentrations, but a significant difference in ECP concentration (p = 0.01) and in MPO concentration (p < 0.0001) in at least one sample population vs one other sample population. Further analyses of the comparisons between two groups showed that NEA patients did not differ from EA patients, but that they had significantly lower ECP and MPO levels compared to COPD patients. Sputum cytology, inflammatory mediators, and stress-related proteins were measured in NEA, EA, and COPD patients. Despite previous evidence of neutrophilia and increased asthma severity in NEA patients, no difference could be detected between NEA and EA patients. Compared to COPD patients, NEA patients showed lower neutrophil counts and lower airway inflammatory and oxidative load. These findings suggest that there might be similarities in airway inflammation between NEA and EA patients, but that NEA patients were clearly different compared to COPD patients.
There are several limitations regarding our study. First, due to the relatively small number of subjects included in the two asthma groups and to the large scatter of values for sputum mediators, the study in these particular comparisons was underpowered. It is obvious that the data from this study are not sufficient to exclude that there are differences in fluid-phase mediators between NEA and EA patients, and that further studies are needed in order to duplicate these findings. Second, all of our subjects were clinically stable and receiving treatment with inhaled steroids. Therefore, it is possible that a significant proportion of patients with EA did not have eosinophilia at the time of our study due to a steroid effect or because they were in a clinically stable condition. We decided to study only steroid-treated subjects for ethical reasons and in order to keep the results between groups comparable. We could have recruited only steroid-naive subjects, but this would have limited us to a smaller population of asthmatic patients with mild disease.
Figure 2. Sputum ECP levels (top left, a), MPO levels (top right, b), IL-8 levels (bottom left, c), and GM-CSF levels (bottom right, d) in NEA patients, EA patients, and COPD patients. The results are expressed as the mean (SEM). See Figure 1 legend for expansion of abbreviation.