Ultrastructural aspects of the adherence to target cells of in vitro differentiated lymphocytes

The specific adherence to target fibroblasts of lymphocytes differentiated in vitro from blast cells after stimulation with pokeweed mitogen was studied under the electron microscope. Lymphocyte pseudopods were seen to penetrate into the target cells forming a close contact between the membranes of the two interacting cells. Microfilaments were the only cytoplasmic components that could be detected within or in the vicinity of the penetrating pseudopods. No morphological signs of secretion could be observed in the contact region. Morphological aspects of the contact region are discussed as related to the lytic mechanism.