Tissue‐specific Differences in Immune Cell Subsets Located in the Naso‐oropharyngeal‐associated Lymphoid Tissues

Defining the immune cells within the naso‐oropharyngeal‐associated lymphoid tissues would promote the development of efficient orally and nasally delivered immunotherapies. The aim was to compare murine antigen‐presenting cells (APC s) and T cell subsets in the nose‐associated lymphoid tissues (NALT ), cervical lymph nodes (CLN ), mesenteric lymph nodes (MLN ) and peripheral lymph nodes (PLN ) using flow cytometry and in vitro proliferation assays. Overall, the NALT contained a higher proportion of APC s and a lower proportion of T cells compared to the CLN , MLN and PLN . The APC s of the NALT more often belonged to the CD 11c⁺CD 11b⁺ and the CD 11c^negCD 11b⁺ subsets as compared to the other sites. Both of these APC populations showed little sign of activation, that is low expression of the markers CD 40, CD 86 and IA d. Instead, the APC s of the NALT more often co‐expressed CX 3CR 1 and CD 206, markers associated with a tolerogenic function. No increase in the proportion of regulatory T cells was observed in the NALT . Instead, the T cells frequently exhibited a memory/effector phenotype, expressing the homing markers α4β7, CCR 4 and CCR 9, but rarely the naïve phenotype cell surface marker CD 45RB . In contrast, the T cells at the other sites were mostly of the naïve phenotype. In addition, cells from the NALT did not proliferate upon in vitro stimulation with Con A, whereas the cells from the other sites did. Taken together, these results suggest that the NALT is primarily an effector site rather than one for activation and differentiation, despite it being regarded as a site of induction.