The use of bronchoalveolar lavage (BAL) to assess lower airways inflammation in asthma

Rationale: While sputum cell counts and proportions have been used to characterise asthma the utility of BAL in phenotyping asthmatic inflammation is less well understood.Method: BAL differential cell counts were obtained from 61 healthy volunteers(H) and 70 mild atopic asthmatics(MA),BTS step 1, 28 moderate asthmatics(MO), BTS step 3, and 81 severe asthmatics(SA), BTS steps 4-5. Median [IQR] percentage differential counts were calculated and group differences were analysed using Mann Whitney U test.Results H median% [IQR] MA median% [IQR] MO median% [IQR] SA median% [IQR] Macrophages 90.3 [83.3-94.1] 86.5 [80.7-91.0]b 81.8 [76.0-89.9]b 78.0 [56.0-90.4]a,c Neutrophils 1.5 [0.8-4.3] 2.0 [1.25-3.0] 2.4 [1.3-7.8] 4.5 [2.0-12.5]a,c,d Epithelial cells 3.6 [0.8-10.0] 7.0 [4.3-10.8] b 7.65 [5.1-17.6]b 9.5 [2.5-20.0]b Eosinophils 0.1 [0.0-0.5] 1.0 [0.3-2.7]a 0.60 [0.0-1.5]b 0.5 [0.1-1.5]a Lymphocytes 1.2 [0.3-3.1] 1.0 [0.3-1.5] 0.625 [0.0-1.5]b 0.5 [0.0-1.3]b,c •a p=<0.001 from healthy, b p=<0.05 from healthy, c p=<0.05 from MA, d p=<0.05 from MOTABLE 1Conclusion: Asthma, independent of severity, was associated with eosinophilic inflammation and increased epithelial shedding in BAL. Neutrophilic airway inflammation was, by contrast, only significantly different from health in severe asthma. In this respect, SA was also different from MA and MO. When the cut off for neutrophilic, eosinophilic and mixed granulocytic BAL was defined as median+2CI for the H patient population, 24% MA, 50% MO and 43% SA samples have results for one of these parameters that was outside of this normal range. These findings indicate the need for at a greater understanding of the relevance of distal airway inflammation to disease persistence in asthma