Contact areas of cytotoxic lymphocytes and target cells. An electron microscopic study.

Using high resolution electron microscopy and specimen tilting, contact zones between lymphocytes and target cells in cultures expressing phytohaemagglutinin (PHA) or antibody-mediated lymphocyte cytotoxicity were examined. No focal membrane changes such as deletions, membrane fusion or junction type of membrane specialization were observed in such areas. The thickness of the plasma membrane of target and effector cells in areas of contact did not differ significantly from that of the membrane elsewhere on the same cells. Cellular interrelations defined as broad zone contact (BC) and point contact (PC) were observed between PHA-stimulated lymphocytes and between effector lymphocytes and target cells. The intercellular distance in BC and PC zones was 150–250 Å. BC type areas were more frequent than PC areas, suggesting that a more stable interaction between cells is mediated by this type of contact.