Ultrastructural study of the relationship between immune cytotoxic lymphoid cells and target cells in vitro.

Ultrastructural details of the relationship in vitro between sensitized T lymphoid cells and YAC target cells are described. Within a few hours very close connections develop between these two cells. Narrow junctions with parallel plasma membranes and local evaginations of the lymphoid cell into recesses of the target cell are specific aspects. Very fine threadlike material is found between the two plasma membranes at the narrowest zones. The lymphoid cells concerned have an intermediate structure between ordinary small lymphocytes and blast cells. They do not seem to be modified in the process while YAC target cells are severly damaged. Polysomes are dispersed; mitochondria and rough endoplasmic reticulum are affected locally or generally. Later, nucleoli and chromatin become dense and pycnosis occurs. The significance of these results is discussed.