Local immunity assessment at seven anatomical sites in the upper and lower airways: High immune cell recovery for detailed cell phenotyping

<bold>Background:</bold> The VAXXAIR project aims to characterise the local airway cellular immune response to influenza vaccination. Here we provide initial data on immune cell recovery from seven different anatomical airway sites. <bold>Methods:</bold> Bronchoalveolar lavage fluid (BALF), bronchial brushing, forceps biopsy, nasopharyngeal (NP) and nasal swabs, endobronchial ultrasound (EBUS)-guided mediastinal lymph node (MLN) biopsy, tonsil fine needle aspiration (T-FNA), tonsil biopsy (TBs), and peripheral blood were collected from 11 healthy volunteers and the samples were processed according to standardised procedures. Absolute leukocyte, lymphocyte (T- and B-cell), CD4 and CD8 T-cell counts were determined using a flow cytometric assay with cell counting beads. <bold>Results:</bold> BALF had the highest cell counts, comparable to those in blood. In NP swabs and MLNs, we observed variation according to sample volume. In nasal swabs and TBs, counts were generally lower and occasionally satisfactory, whereas bronchial brushings and T-FNAs mostly yielded leukocyte counts below 10⁵/mL (<italic>Figure 1</italic>). <fig><object-id>erj;66/suppl_69/PA4246/F1</object-id><object-id>F1</object-id><object-id>F1</object-id><graphic></graphic></fig> <bold>Conclusions:</bold> Cellular phenotypic characterisation is feasible on BALF, NP swabs, and MLNs, and possibly also on nasal swabs and TBs after further methodological optimisation. The next step in VAXXAIR is to apply the above methods in a randomised trial with different influenza vaccines. <italic>^{*JUSJ and HVM share last authorship}</italic>