Characterizing T cell subsets in the nasal mucosa of children with acute respiratory symptoms.

Background: In infants admitted to an ICU with respiratory failure, there is an association between the ratio of CD8 to CD4 T cells within the upper respiratory tract and disease severity. Whether this ratio is associated with respiratory disease severity within children presenting to a pediatric emergency department is not known.

Methods: We studied a convenience sample of 63 children presenting to a pediatric emergency department with respiratory symptoms. T cell subsets in the nasal mucosa were analyzed by flow cytometry. We compared CD4 and CD8 T cells subsets in these samples and analyzed the proportion of these subsets that expressed markers associated with tissue residency.

Results: We were able to identify major subsets of CD8 and CD4 T cells within the nasal mucosa using flocked swabs. We found no difference in the ratio CD8 to CD4 T cells in children with upper or lower respiratory illness. A positive association between tissue-resident memory T cell frequency and patient age was identified.

Conclusions: In our patient populations, the CD8:CD4 ratio was not associated with disease severity. The majority of T cells collected on nasal swabs are antigen experienced, and there is an association between the frequency of tissue-resident T cells and age.

Impact: Immune cell populations from the nasal mucosa can be captured using flocked nasal swabs and analyzed by flow cytometry. Nasal CD8:CD4 ratio does not predict respiratory illness severity in children presenting to the emergency department. The frequency of CD8 and CD4 resident memory T cells within the nasal mucosa increases with age.