Subsets of tonsillar lymphocytes and activated cells in each subset analysed by three-color flow cytometry.

Among the four subsets of tonsillar T cells, active cells were most abundant in the helper T subset, followed by the cytotoxic T, inducer T, and suppressor T subsets in order of decreasing cell count. The number of active cells was very small in the suppressor T subset. Plasma cells (PCA-1-positive cells) accounted for only about 3% of tonsillar cells. However, nearly half of the tonsillar B cells were activated (positive for Ba, being either Ba+/IgD+ or Ba+/IgD-). Ba-positive cells were hardly found in the population of peripheral-blood B cells. Ba+/IgD+ cells, which are ready to be transformed to cyclic cells or dormant cells depending upon the degree of stimulation, outnumbered cyclic cells. Many Ba+/IgD+ cells were present even in the small tonsils of adults, although these cells were very scarce in the peripheral blood. These findings show that the tonsil is prepared to perform immunologic functions in prompt response to external stimuli.