Background
Changes in pulmonary surfactant lipid composition are suggested to influence the inflammatory respons in asthma. 

Aim
To examine changes in surfactant lipid composition in subjects with allergic asthma, both during and outside pollen-season.

Methods
23 subjects with allergic asthma and 13 healthy controls were examined during pollen-seasons 2016, 2017 and in November 2017, with spirometry, single breath nitrogen wash out test (SNIII), ACQ-test, and PExA, i.e. samples of surfactant from the small airways analyzed with triple quadrupole mass spectrometry. Mixed models and multivariate analysis were perfomed using SAS^© and SIMCA^©.  

Results
Surfactant lipid composition were altered in allergic asthma outside the pollen season, but the largest differences to healthy controls were found in the pollen seasons. Among the lipid-classes Phosphatidyl-Inositols were lower in asthma, and among individual lipid-species many phosphatidyl-glycerol species were increased in asthma. Among the Phosphatidyl-Cholines, PC14:0_14:0  was 23% higher in both pollen-seasons in asthma (p<0,05), but similar to healthy controls outside pollen-season. 

5 out of 9 lipids that were significantly associated with lower level of asthma-control contained PC20:4 (arachidonic acid), and were all lower in those with poor control.

The slope of SNIII were significantly associated with the levels of 27 lipid-species, but was only significantly lower in asthma outside pollen-season (1.8±1,1 vs 1,1±0,6, p=0,05).

Conclusion
There are differences in surfactant lipid composition between subjects with allergic asthma and healthy controls that may interplay with the inflammatory response to birch-pollen and affect level of control.