A cloned cell with NK function resembles basophils by ultrastructure and expresses IgE receptors

Natural killer (NK) cells are defined by their ability to lyse certain tumour cells in vitro without previous exposure to them^1-5, and have been postulated as effectors of immune surveillance against spontaneous neoplasms⁶. Because they kill some non-neoplastic lymphoid cells, they may also have a role in immunoregulation^7,8. NK cell activity resides in a small proportion of normal mouse spleen cells (<5%) that have been difficult to characterize completely. They may represent a heterogeneous group of effector cells whose precise relationship to other myelopoietic or immunological cells has remained obscure^9-12. We have previously described a cloned mouse cell line (Cl. Ly 1^-2^-NK-1 ⁺/11) with the functional characteristics of natural killer cells activated by interferon or other factors⁸. We now find that this cloned line, like basophils^13,14 and mast cells¹⁵, expresses high-affinity plasma membrane receptors (Fc_∈R) specific for IgE antibody. In addition, the clone contains cytoplasmic granules similar by ultrastructure to those of basophils of the mouse and other species. Our findings indicate that cells sharing morphological and biochemical features of basophilic granulocytes can mediate NK lysis.