CD3 is the most specific T cell antibody, commonly used to identify T cells in benign and
malignant disorders. Staining is both membranous and cytoplasmic. It is usually used in
combination with CD20 in an initial evaluation of lymphoid processes to determine T and B cell populations.
CD3 also stains NK cells and thus is used to define NK lymphoma. In this condition, staining is
cytoplasmic, not membranous. In the central nervous system, CD3 stains Purkinje cells of the
cerebellum. Nonspecific cytoplasmic staining may be seen in plasma cells and macrophages.