Dynamics of memory cell subsets in human tonsils with age: impact on the functional reconfiguration of the organ

Background. The palatine tonsils are lymphoepithelial structures in which immune responses to inhaled and ingested pathogens are mounted. While we have previously shown that tonsillar immune effector function declines with age, the impact of such erosion on the local viral reservoirs or in specific memory responses remains to be defined. Methods. We performed phenotypic and functional characterization of tonsillar mononuclear cells (TMC) and tissue biopsies from a cohort of around 80 patients (ages 1–45). We quantified the proportion of particular lymphoid subsets associated with ageing through flow cytometry. We also assessed the expression of LMP-1 and EBNA-2, latency proteins of Epstein-Barr virus (EBV), via immunohistochemistry. Finally, we functionally tested the specific response of tonsillar memory B cells distantly induced by tetanus toxoid (TT) injection, through ELISA on the supernatant of TT- stimulated TMC cultures. Results. We demonstrated a significant age-dependent decline in the B cell proportion balanced by a concomitant rise in the T cell fraction. This shift was complemented by the accumulation of particular phenotypes associated with aged B cells and senescent T cells. Despite these alterations, tonsillar samples from older patients presented a more effective repression of EBV viral antigens (Ag) than those of younger children. We also established that TMC from all patients tested harboured responsive TT specific memory B cells and moreover, anti-TT Ig production correlated with the time since the last vaccination. Conclusion . Our findings suggest that tonsillar involution constitutes a functional transition from a germinal centre driven secondary lymphoid organ in childhood to a memory dominated, immunoregulatory reservoir in adulthood. This reconfiguration preserves local viral control and serves to integrate both local and systemic immunological memory.