Background

Eosinophil counts are elevated within a subgroup of COPD patients. Increased immune cell infiltration is a feature of small airway (SA) disease in COPD. We investigated the effect of disease and smoking status on eosinophil counts  in the sub-epithelial (SE) and intra-epithelial (IE) regions of SA.

Methods

Eosinophils in SA were identified by LUNA stain. IE and SE eosinophil counts from 48 COPD patients and 27 smoking controls (S) were recorded.

Results

COPD patients had higher IE eosinophil counts versus S (median=93.1 vs 7.9 cells/mm² respectively, p=0.01, Figure 1A); SE counts were not different. IE eosinophil counts were lower in COPD current- versus ex-smokers (48.0 vs 189.1 cells/mm² respectively, p=0.04, Figure 1B). SE counts were not different. GOLD stage and ICS use did not influence eosinophil counts.

Figure 1: Number of IE eosinophil count /mm² for COPD versus S (A) and COPD current- (COPDS) versus ex-smokers (COPDE) (B). n=48, 27, 26 and 22 respectively. *, p<0.05.

Conclusion

In the SA, enhanced eosinophilic infiltration in COPD is present in the IE region, not the SE. Current smoking reduced IE eosinophil counts, indicating reduced type 2 inflammation in COPD current smokers. This mechanism may explain the reduced ICS response associated with current smoking in some clinical trials.