null cell [L, nullus, not one, cella, storeroom] , a lymphocyte that develops in the bone marrow and lacks the characteristic surface markers of the B and T cells (surface immunoglobulin or the pan-T antigen). Null cells represent a small proportion of the lymphocyte population. Stimulated by the presence of an antibody, null cells can attack certain cellular targets directly. They kill tumor or viral-infected cells, although not with the specificity of cytotoxic T cells. A null cell is a type of natural killer cell. The term null cell is no longer in common use. Compare B cell, T cell. See also cytotoxin, immune gamma globulin, natural killer cell.
