Naturally cytotoxic tonsillar leukocytes: phenotypic characterization of the effector population

Human palatine tonsil sections were examined to investigate the distribution of cells bearing the cell surface markers of peripheral blood natural killer (PB-NK) cells. Leu-7+ (HNK-1+) cells were localized predominantly in lymphoid follicles, whereas OKM1-, Mac-1-, and Mo2-labelled cells were found in the epithelial and subepithelial regions and epithelial crypts. OKT10+ cells showed a variable distribution, being found in follicles and interfollicular or subepithelial regions. No. B73.1+ cells could be identified in tonsil sections. Leu-7+ cells appeared not to be responsible for tonsillar natural cytotoxicity, since Leu-7 (HNK-1) antibody- and complement-mediated lysis under conditions that markedly reduced PB-NK activity failed to abolish cytotoxicity, and positive selection by means of the FACS IV gave no enrichment of activity. Similarly, cells labelled with the antibodies B73.1, Leu-11b, OKT8, OKT10, and TDR 31.1 (anti-major histocompatibility complex class II framework determinant) were not enriched with regard to NK activity either. However, positive selection with OKM1, Mac-1, or Mo2 showed that cells bearing these markers were responsible for essentially all tonsillar NK activity. No large granular lymphocytes were identified in such populations enriched for NK activity. The observation that PB-NK cells labelled faintly with Mo2 weakens the argument that a non-adherent mononuclear phagocyte population was responsible for the activity. These data therefore support the existence of heterogeneity within naturally cytotoxic cell populations.